How to avoid a distorted Android camera preview with ZXing.Net.Mobile [Updated]

How to avoid a distorted Android camera preview with ZXing.Net.Mobile [Updated]

Update: The application I used to determine this blog post is portrait only, that’s why I totally missed the landscape part. I have to thank Timo Partl, who pointed me to that fact on Twitter. I updated the solution/workaround part to reflect the orientation as well.

If you need to implement QR-scanning into your Xamarin (Forms) app, chances are high you will be using the ZXing.Net.Mobile library (as it is the most complete solution out there). In one of my recent projects, I wanted to exactly that. I have used the library already before and thought it might be an easy play.

Distorted reality…

Reality hit me hard when I realized that the preview is totally distorted:

distorted camera preview

Even with that distortion, the library detects the QR code without problems. However, the distortion is not something you want your user to experience. So I started to investigate why this distortion happens. As I am not the only one experiencing this problem, I am showing to easily fix that issue and the way that led to the solution (knowing also some beginners follow my blog).

Searching the web …

.. often brings you closer to the solution. Most of the time, you are not the only one that runs into such a problem. Doing so let me find the Github issue above, showing my theory is correct. Sometimes, those Github issues provide a solution  – this time, not. After not being able to find anything helpful, I decided to fork the Github repo and downloaded it into Visual Studio.


Once the solution was loaded in Visual Studio, I found that there are some samples in the repo that made debugging easy for me. I found the case that matches my implementation best (using the ZXingScannerView). After hitting the F10 (to move step by step through the code) and F11 (to jump into methods) quite often, I understood how the code works under the hood.

The cause

If you are not telling the library the resolution you want to have, it will select one for you based on this rudimentary rule (view source on Github):

// If the user did not specify a resolution, let's try and find a suitable one
if (resolution == null)
    foreach (var sps in supportedPreviewSizes)
        if (sps.Width >= 640 && sps.Width <= 1000 && sps.Height >= 360 && sps.Height <= 1000)
            resolution = new CameraResolution
                Width = sps.Width,
                Height = sps.Height

Let’s break it down. This code takes the available resolutions from the (old and deprecated) Android.Hardware.Camera API and selects one that matches the ranges defined in the code without respect to the aspect ratio of the device display. On my Nexus 5X, it always selects the resolution of 400×800. This does not match my device’s aspect ratio, but the Android OS does some stretching and squeezing to make it visible within the SurfaceView used for the preview. The result is the distortion seen above.

Note: The code above is doing exactly what it is supposed to do. However, it was updated last 3 years ago (according to Github). Display resolutions and aspect ratios changed a lot during that time, so we had to arrive at this point sooner or later.


The solution to this is pretty easy. Just provide a CameraResolutionSelectorDelegate with your code setting up the ZXingScannerView. First, we need a method that returns a CameraResolution and takes a List of CameraResolution, let’s have a look at that one first:

public CameraResolution SelectLowestResolutionMatchingDisplayAspectRatio(List<CameraResolution> availableResolutions)
    CameraResolution result = null;

    //a tolerance of 0.1 should not be visible to the user
    double aspectTolerance = 0.1;
    var displayOrientationHeight = DeviceDisplay.MainDisplayInfo.Orientation == DisplayOrientation.Portrait ? DeviceDisplay.MainDisplayInfo.Height : DeviceDisplay.MainDisplayInfo.Width;
    var displayOrientationWidth = DeviceDisplay.MainDisplayInfo.Orientation == DisplayOrientation.Portrait ? DeviceDisplay.MainDisplayInfo.Width : DeviceDisplay.MainDisplayInfo.Height;

    //calculatiing our targetRatio
    var targetRatio = displayOrientationHeight / displayOrientationWidth;
    var targetHeight = displayOrientationHeight;
    var minDiff = double.MaxValue;

    //camera API lists all available resolutions from highest to lowest, perfect for us
    //making use of this sorting, following code runs some comparisons to select the lowest resolution that matches the screen aspect ratio and lies within tolerance
    //selecting the lowest makes Qr detection actual faster most of the time
    foreach (var r in availableResolutions.Where(r => Math.Abs(((double)r.Width / r.Height) - targetRatio) < aspectTolerance))
            //slowly going down the list to the lowest matching solution with the correct aspect ratio
            if (Math.Abs(r.Height - targetHeight) < minDiff)
            minDiff = Math.Abs(r.Height - targetHeight);
            result = r;                

    return result;

First, we are setting up a fixed tolerance for the aspect ratio. A value of 0.1 should not be recognizable for users. The next step is calculating the target ratio. I am using the Xamarin.Essentials API here, because it saves me some code and works both in Xamarin.Android only projects as well as Xamarin.Forms ones.

Before we are able to select the best matching resolution, we need to notice a few points:

  • lower resolutions result in faster QR detection (even with big ones)
  • preview resolutions are always presented landscape
  • the list of available resolutions is sorted from biggest to smallest

Considering these points, we are able to loop over the list of available resolutions. If the current ratio is out of our tolerance range, we ignore it and move on. By setting the minDiff double down with every iteration, we are moving down the list to arrive at the lowest possible resolution that matches our display’s aspect ratio best. In the case of my Nexus 5X 480×800 with an aspect ratio of 1.66666~, which matches the display aspect ratio of 1,66111~ pretty close.

Delegating the selection call

Now that we have our calculating method in place, we need to pass the method via the CameraResolutionSelectorDelegate to our MobileBarcodeScanningOptions.

If you are on Xamarin.Android, your code will look similar to this:

var options = new ZXing.Mobile.MobileBarcodeScanningOptions()
   PossibleFormats = new List<ZXing.BarcodeFormat>() { ZXing.BarcodeFormat.QR_CODE },
CameraResolutionSelector = new CameraResolutionSelectorDelegate(SelectLowestResolutionMatchingDisplayAspectRatio)

If you are on Xamarin.Forms, you will have to use the DependencyService to get to the same result (as the method above has to be written within the Android project):

var options = new ZXing.Mobile.MobileBarcodeScanningOptions()
   PossibleFormats = new List<ZXing.BarcodeFormat>() { ZXing.BarcodeFormat.QR_CODE },
CameraResolutionSelector = DependencyService.Get<IZXingHelper>().CameraResolutionSelectorDelegateImplementation

The result

Now that we have an updated resolution selection mechanism in place, the result is exactly what we expected, without any distortion:

matching camera preview


In case none of the camera resolutions gets selected, the camera preview automatically uses the default resolution. In my tests with three devices, this is always the highest one. The default resolution normally matches the devices aspect ratio. As it is the highest, it will slow down the QR detection, however.

The ZXing.Net.Mobile library uses the deprecated Android.Hardware.Camera API and Android.FastCamera library on Android. The next step would be to migrate over to the Android.Hardware.Camera2 API, which makes the FastCamera library obsolete and is future proof. I had already a look into that step, as I need to advance in two projects (one personal and one at work) with QR scanning, however, I postponed this change.


For the time being, we are still able to use the deprecated mechanism of getting our camera preview right. After identifying the reason for the distortion, I got pretty fast to a workaround/solution that should fit most use cases. As devices and their specs are evolving, we are at least not left behind. I will do another writeup once I found the time to replace the deprecated API in my fork.

As always, I hope this post will be helpful for some of you.

Until the next post, happy coding, everyone!

Title Image Credit

Posted by msicc in Android, Xamarin, 5 comments
Crypto and Blockchain projects & tools (April 2019)

Crypto and Blockchain projects & tools (April 2019)

NOTE: All following project and tools reflect my own opinion and my own experience. This post is not an investment advice or advice to use them. Also, your mileage may vary. Please make sure you also read the disclaimer at the end of this post as well. This post contains affiliate/referral links.

For Users

Mass adoption. If you keep following the crypto and blockchain space, you might have heard this term a lot. At the moment, besides gambling dApps (decentralized applications) on different blockchains, there are only a few real-world products floating around. Let’s have a look at some of them.


Presearch is a decentralized search engine that has more than 1 million users (as of writing this), which is quite impressive for a beta product, especially in this special area. Presearch tries to disrupt the dominance of Google (which acts as the gate to the internet for more than 70% of all users).

I have been using Presearch for a few months now as my personal gate to the internet, and I enjoy the aggregation of my preferred search engines. If you look at my start page, you can see all the search providers I have chosen. From Bing, Google to Github as well as iTunes and Spotify, everything gets searched with a click. If you open a new Tab with Presearch, you can filter the search once more. I often use the Presearch engine search, which just delivers the best results for me. I am helping the product to evolve with this behavior, as a little bonus, I get 0.25 PRE(search token) for the searches I perform.


Presearch has protection against cheaters (AI powered) in place. I am obviously not cheating to help the product, and my honesty is rewarded with an account level of 9. They have a Chrome extension which sets the current search engine (Desktop) just by installing it. Presearch even has a mobile app (beta, iOS), which is currently not able to connect to your account which I use from time to time. However, as happened with Bing and Google before, I am using their mobile website most of the time on my iPhone.

Brave Browser

If you have been following me for some time, you know that I am a fan of Microsoft. Recently, however, Microsoft turned into a more business-oriented company, leaving the consumer to just go with the products of other providers. This led me to search for alternatives of my personal browser – so I ended up with Brave Browser.

Brave aims to be faster and more private than the default choices users have. Websites store all kind of data in cookies and use trackers to collect data from a user while the later one is browsing the web. With Brave, you get back a good amount of control of the data you are willing to share. Over time, your privacy level will grow again just by using Brave. The browser shows you how many trackers, cookies and scripts were blocked while you are browsing.

Since a few weeks, user can receive rewards for watching ads. Users will be prompted to view ads (mostly short videos), and receive some BAT, the native currency of Brave – which they can use again to reward content creators. This is an opt-in feature, so users always have the choice.

If you have a blog, website or YouTube channel, you can help the project to grow. Register your site/channel as a creator, and use your BAT rewards to tip others and invite them to join, too. This way, knowledge about Brave will spread across the web from all sides.


CoinPaprikais a market analysis tool, and it is a powerful one. I discovered the project last summer (shortly after they started). I like it “hot and spicy”, so the name alone immediately called my attention. As I have two or three app ideas that need a service like CoinPaprika, I was happy to learn they have an open API as well, with really generous API rate limits. I am contributing to the project in the form of maintaining a .NET library.


CoinPaprika is somewhat different to other providers, as they do not rely on data of CoinMarketCap (which a lot of services in this area do). Instead, they are pulling in data of more than 250 exchanges on their own, resulting in over 2000 currencies they track. On top, they provide a great oversight on each project (click the coin stats links above to see some samples).

They are also working on a mobile app, which will combine their analysis tools with a non-custodial wallet (based on Trust Wallet’s core). You can get a short overview and register for beta notification at


AtomicPay is a non-custodial payment service provider. While there are quite some providers of such services floating around, AtomicPay holds the flag of decentralization pretty high. The service just provides the invoicing infrastructure, while the payment itself is only tracked by the system. The effective payment is a direct customer to merchant transaction – the funds move directly into the merchant’s wallet. The whole infrastructure is built around Electrum and its derivations for other currencies.


By using common implementations like SegWit and HD (Hierarchical Deterministic) wallets as well as no address re-use, AtomicPay ensures security and privacy on a high level with a reasonable amount of initial administrative work. AtomicPay provides several integrations into already existing online shopping systems, an open Rest-API, payment buttons for websites and more.

I am also involved in this project and currently working on the official native apps for Android and iOS. We have already published a .NET SDK, which enables you already today to implement crypto payments into your apps. On our roadmap, we have a Xamarin.Forms ready plugin and SDKs for other programming languages as well.

For Developers

Being a mature programming language, C# has already quite some important and ready-to-use libraries to interact with certain blockchains. Here is a list of projects I am following:

Wallets and Exchanges

If you want to get some cryptocurrencies, you need some starting points:

  • Where to buy?
  • Where to convert/exchange?
  • Where to store HODLs?

While there are several options out there, I have found a combination that works for me.


Buying crypto currencies with bank transfer or credit card is pretty easy on BitPanda, an Austrian provider. They accept deposits in EUR, CHF, USD and GBP. Once your FIAT deposit is in your BitPanda account, you can exchange them for a variety of crypto currencies including Bitcoin, Ethereum, NEO and more. If you want to sign up and get a 10 EUR bonus after your first purchase, you can use my referral link (I am getting the bonus as well).


Binance is one of the biggest centralized crypto exchanges around. They have a huge amount of tradeable assets and also great liquidity. If a trading pair is available on Binance, chances are high that you will get the best price there. Their apps and website offer a good default set of indicators, so you normally won’t need any additional tools. Binance is also said to be one of the few exchanges to not fake their trading volume. If you haven’t signed up to Binance, feel free to use my referral link.


ChangeNOW is a decentralized exchange that is connected to big centralized exchanges to get the best rates. On certain pairs, you have a fixed rate option besides the quick-and-dirty approach that all such services provide. However, if you use that one, you will get a smaller exchange value than with the default option because of lowering the risk. In my experience, the exchange rates reflect the current market prices more often than not. Other providers have a bigger spread.

Transactions are executed as fast as possible, if something goes wrong and you provide your wallet for refunds, your funds will always be safe. Additionally, you can provide your mail address to get informed when the exchange took place (so you won’t need to constantly refresh the website).


KyberSwapis another decentralized exchange, but just for Ethereum tokens (at least at them moment of writing this). It is based on the Kyber protocol, which allows fast and direct swaps of tokens (for example BAT=>KNC) without the need of exchanging first to Ethereum and then into the desired token. There are already quite a few dApps built on the Kyber protocol, you can see a list here. Recently, KyberSwap launched a nice and easy to use iOS app, which supports also a price alert feature (USD and ETH base pairs only, however).

Trust Wallet

Trust Wallet, the official non-custodial wallet of Binance, has a good reputation when it comes to storing your HODLs. It is available for both Androidand iOS, with a desktop version being worked on. They are constantly adding new coins, and the usage is even for new users pretty easy. Their Telegram support group is always just a message away in case you need some help.

MyEtherWallet and MEWConnect

If you want to perform advanced operations (like cleaning pending transactions or getting your *.eth address), there is a big chance that you will be able to do it with MyEtherwallet.

They recently launched a newer version of their website. However, not all functionality has been ported over (yet). If you cannot find an option on the new site, you will find it for sure at their vintage site. The most secure way to connect to MyEtherWallet is their MEWConnect app (available for iOS and Android), which transforms your phone into a hardware wallet-like device. You need to confirm transactions on the device before you can move on in the browser, adding in an additional security layer.


Etherscan is the best known Ethereum blockchain explorer around. It has tons of features, from viewing transactions or contracts to token details and ENS-Lookup. Whenever I need to verify or search something related to the Ethereum blockchain, this is my first goto-address.

O3 Wallet (NEO)

If you are searching for blockchains built with .NET, sooner or later you will run into NEO. I only recently began to explore the possibilities of the NEO blockchain and its native currency. NEO has a token ecosystem as well. IF you need a cross-platform wallet, I would give the O3 wallet a try. It integrates with Switcheo (another decentralized exchange) and quite a few other dApps (like registering your .neo address via NNS) running on NEO.

New projects

The crypto space never stand still. New projects are showing up almost every day. Here is a list of projects I recently started to discover. It is way to early to write a review on them, but I may do so in a follow up post.

  • WolfpackBot (beta, crypto trading bot running on its own blockchain)
  • Bravo (write reviews, receive crypto)
  • Switcheo (decentralized exchange for NEO and ETH tokens, EOS soon)
  • Electroneum (mobile (cloud) mining on its own blockchain, use 5576A9 to get a 1% bonus on your mining rewards (5% for me))

News Sources

It is always good to know what is going on in the crypto space. Here are some reliable news sources I use:


Besides the hundreds (if not thousands) of gambling dApps across all blockchains, there are also interesting real word projects one can use today. Some of them are more popular than others, but not every project is worth your attention. This post showed some of the projects I am interested in.

If you know a project/tool/dApp that is missing in this list, feel free to leave a comment below or ping me on social networks. Maybe your suggestions will make it into the next post of this kind.

Disclaimer: I am contributing to one or more crypto/blockchain projects with code written by me under the MIT License. Future contributions may contain their own (and different) disclaimer. I am not getting paid for my contributions to the project at the moment of writing this.

Please note that none of my crypto related posts is an investment or financial advice. As crypto currencies are volatile and risky,  you should only invest as much as you can afford to lose. Always do your own research!

Title Image Credit

Posted by msicc in Crypto&Blockchain, Editorials, 0 comments
Handle AtomicPay’s webhook with Microsoft Azure (Part 3/3) – sending push notifications with Notification Hub

Handle AtomicPay’s webhook with Microsoft Azure (Part 3/3) – sending push notifications with Notification Hub

Series overview

  1. Handle the incoming notification with an Azure Function (first post)
  2. Verify the invoice state within the Azure Function, but store the API credentials in the most secure way (second post)
  3. Send a push notification via Azure Notification Hub to all devices that have linked a merchant’s account to it (this post)


With Azure Notification Hub, we have one of the most powerful tools for sending push notifications out to connected devices. It is designed to handle multiple platforms, so let’s create a new Notification Hub in the Azure Portal. After logging in, select ‘Create a resource‘, followed by ‘Mobile‘ and a final click on ‘Notification Hub‘:

Azure: create a new Notification Hub

Fill in the details of the new Hub. Remember to select your already existing Resource Group and the same region that is used for your Azure Function:

Azure: new Notification Hub creation details

After about a minute, your newly created Notification Hub is ready to use. Select ‘Go to resource‘ to open it.

Azure Deployment finished

Now we are already able to connect to our first platform. For this sample, I will focus on Android. Login to the Firebase console with your Google account. Select ‘Add project‘ and configure your Android app (or add your existing, if you have already one like I do):

Firebase: Add or select project

After following all (self-explanatory) steps, scroll a bit down in the General tab of your Firebase project. You will find an entry like this:

Firebase: download google-services.json file

Download the ‘google-services.json‘-file. We will need it later in our Android app. Now select the ‘Cloud Messaging‘ tab. You will be presented with two keys – copy the upper one:

Firebase: copy server key

Go back to the Azure portal and select ‘Google (GCM/FCM)‘ in ‘Settings’ . Paste the earlier copied key and hit the ‘Save‘-Button:

Azure: paste Firebase server key and save

Now we need to authenticate our Azure Function to the Notification Hub. Select ‘Access Policies‘ in the ‘Manage’ section of your Hub and copy the lower ConnectionString with the ‘Listen,Manage,Send permission:

Azure: copy server ConnectionString

Open your Azure Function in a new tab. In the ‘Application settings‘, add a new setting and paste the ConnectionString. Add another one for the NotificationHub’s name:

Azure Function add Hub name and ConnectionString to Application settings

Go back to the Notification Hub and save the upper ConnectionString locally, as we need that one in our Android application later on

Back to code…

Now that we have prepared the Notification Hub on Azure, let’s write some code that actually sends out our notifications once our Function verified our AtomicPay invoice. In the last post, we already rewrote some of the code in preparation of the final step, our push notifications.

Triggering push notifications

Before we will be able to modify our Function code to actually send the notification, we need to install an additional NuGet package: Microsoft.Azure.Webjobs.Extensions.NotificationHub. Please note that I only was able to get this all up and running with version 1.2.0, version 1.3.0 seems to be not compatible with v1 Functions.

Triggering push notifications can be broken down into these 3 steps:

  1. create a Hub client from the ConnectionString
  2. create the content of the notification
  3. finally send the notification

This translates into this Task inside our InvoiceVerifier class:

        private static async Task TriggerPushNotification(InvoiceInfoDetails invoiceInfoDetails, string accId)
            //we need full shared access connection string (server side)
            var connectionString = ConfigurationManager.AppSettings["NotifHubConnectionString"];
            var hubName = ConfigurationManager.AppSettings["NotifHubName"];

            var hub = NotificationHubClient.CreateClientFromConnectionString(connectionString, hubName);

            var templateParams = new Dictionary<string, string>();
            templateParams["body"] = $"Received payment for invoice id: {invoiceInfoDetails.InvoiceId} ({invoiceInfoDetails.Status.ToString()})";

            var outcome = await hub.SendTemplateNotificationAsync(templateParams, $"accId:{accId}");

            _traceWriter.Info($"attempted to inform merchant {accId} of payment via push");

We are loading the ConnectionString and the Hub’s name from our Function’s Application settings and create a new client connection using these two safely stored properties. To keep this sample simple, I am using a templated notification that can be used across all supported platforms. The receiver is responsible for the handling of this template (we’ll see how later in this post). Finally, we are sending out the notification to the native platforms, where they will be distributed (in our case, via Firebase Cloud Messaging). By including the accId:{accId}tag, we are sending the push notification only to the devices that were registered with that specific merchant account.

Of course, this nicely written method does nothing until we actually use it. Let’s update our Run method. we only need to add one line for our test in the switch that handles the returned invoiceInfoDetails:

switch (invoiceInfoDetails.Status)
	case AtomicPay.Entity.InvoiceStatus.Paid:
	case AtomicPay.Entity.InvoiceStatus.PaidAfterExpiry:
	case AtomicPay.Entity.InvoiceStatus.Overpaid:
	case AtomicPay.Entity.InvoiceStatus.Complete:
		log.Info($"invoice with id {invoiceInfoDetails.InvoiceId} is paid");
		await TriggerPushNotification(invoiceInfoDetails, accId);
		log.Info($"invoice with id {invoiceInfoDetails.InvoiceId} is not yet paid");
		//todo: this will trigger additional status handling in future

Publish your updated Azure Function. Our Azure Function is now connected to a Notification Hub and is able to send out push notifications. Of course, push notifications ending in Nomandsland are boring. So let’s go ahead.

Receiving the push notifications

Create a new Xamarin.Android app (with XAML or without, your choice). Of course, also here we have some additional setup to perform.

Import google-services.json

Add the google-services.json we downloaded before from Firebase to your project. Set its Build Action to GoogleServicesJson in the Properties window. I needed to restart Visual Studio to be able to select this option after adding the file.


Installing NuGet packages

Of course, we also need to install some additional NuGet packages:

The second step involves some changes to the AndroidManifest, giving the Firebase package some permissions and handle its intents in the application tag:

<receiver android:name="" android:exported="false" />
<receiver android:name="" android:exported="true" android:permission="">
		<action android:name="" />
		<action android:name="" />
		<category android:name="${applicationId}" />

Next, we will add a new constants class:

public static class Constants
	public const string ListenConnectionString = "<Listen connection string>";
	public const string NotificationHubName = "<hub name>";

On the client, we are only using the lower permission ConnectionString we copied earlier from the Azure Notification Hub.

Connecting to Firebase

As our Azure Notification Hub sends notifications via Firebase, Google’s native messaging handler, we need a service that connects our app. The service requests a token (the Xamarin library does all that complex stuff for us) that we’ll need to actually register the device for the notifications. Add a new class called PlatformFirebaseIidService and decorate it with the Service attribute. Besides that, we need to register our interest on the, which will call into the OnTokenRefresh() method we will override. We’ll end up like this:

[IntentFilter(new[] { "" })]
public class PlatformFirebaseIidService : FirebaseInstanceIdService
	const string TAG = "PlatformFirebaseIidService";
	NotificationHub _hub;

	public override void OnTokenRefresh()
		var refreshedToken = FirebaseInstanceId.Instance.Token;
		Log.Debug(TAG, "FCM token: " + refreshedToken);		

Now that we hold a fresh Firebase instance token, we can register our app for receiving push notifications. To do this, we’re adding an new method:

void SendRegistrationToServer(string token, List<string> tags = null)
	// Register with Notification Hubs
	_hub = new NotificationHub(Constants.NotificationHubName, Constants.ListenConnectionString, this);

	if (tags == null)
		tags = new List<string>() { };

	var templateBody = "{\"data\":{\"message\":\"$(body)\"}}";

	//this one registers a template that can be used cross platform
	//just make sure the template is the same on iOS, Windows, etc.
	var registerTemplate = _hub.RegisterTemplate(token, "defaultTemplate", templateBody, tags.ToArray());
	Log.Debug(TAG, $"Successful registration of Template {registerTemplate.RegistrationId}");

Let me break this method down. Of course, we need to connect to our Notification Hub, which is responsible for the decision if our client is a valid receiver or not. If we add tags, they will get send together with the registration. We will add the merchant’s account Id to filter the receiver. As we are sending notifications using a template, we need to register for the template that gets filled by our Azure Function. One thing is left, calling this method after obtaining a token in the OnTokenRefresh override:

SendRegistrationToServer(refreshedToken, new List<string>() { "accId:<yourAccId>" });

Handling incoming firebase messages

Now that our client is registered with both Firebase and the Azure Notification Hub, of course we want it to be able to receive the pushed messages. To achieve this, we need another Service. Add a new class called PlatformFirebaseMessagingService and decorate it once again with the Service attribute. This time, we are interested in the intent, so let’s add also this one. The service is responsible for parsing our payload and actually trigger a notification helper to send the notification. Here is the code of the service:

[IntentFilter(new[] { "" })]
public class PlatformFirebaseMessagingService : FirebaseMessagingService
	const string TAG = "PlatformFirebaseMessagingService";

	public override void OnMessageReceived(RemoteMessage message)
		Log.Debug(TAG, "From: " + message.From);
		string title = "Azure Test message";
		string body = null;

		if (message.GetNotification() != null)
			//These is how most messages will be received
			body = message.GetNotification().Body;
			title = message.GetNotification().Title;
			Log.Debug(TAG, $"Notification Message Body: {body}");
			//Only used for debugging payloads sent from the Azure portal
			body = message.Data.Values.First();

		var notification = NotificationHelper.Instance.GetNotificationBuilder(title, body);
		NotificationHelper.Instance.Notify(1001, notification);


Of course, you are curious about the NotificationHelper class. Let’s have a look. Besides being a Singleton, we need to retrieve an instance of the system’s NotificationService. As we do not have multiple notification channels in this sample, it is enough to declare both the name and its id in two constants. In the constructor of the class, we are initializing the channel:

public class NotificationHelper : ContextWrapper
	private static NotificationHelper _instance;

	public static NotificationHelper Instance => _instance ?? (_instance = new NotificationHelper(Application.Context));
	const string NOTIFICATION_CHANNEL_ID = "default";
	const string NOTIFICATION_CHANNEL_NAME = "notif_test_channel";

	NotificationManager _manager;
	NotificationManager Manager => _manager ?? (_manager = (NotificationManager)GetSystemService(NotificationService));

	public NotificationHelper(Context context) : base(context)
		var channel = new NotificationChannel(NOTIFICATION_CHANNEL_ID, NOTIFICATION_CHANNEL_NAME, NotificationImportance.Default);
		channel.LockscreenVisibility = NotificationVisibility.Public;

Creating the Notifications involves the Notificiation.Builder class. We’re simplifying the process for us with this method:

public Notification.Builder GetNotificationBuilder(string title, string body)
	var intent = new Intent(this.ApplicationContext, typeof(MainActivity));
	var pendingIntent = PendingIntent.GetActivity(this, 0, intent, PendingIntentFlags.OneShot);

	return new Notification.Builder(this.ApplicationContext, NOTIFICATION_CHANNEL_ID)

To read more about creation notifications, have a look at the docs for local (= client side) notifications.

Last but not least, we need to inform the system’s notification service to show the notification. The final helper method to this looks like this:

public void Notify(int id, Notification.Builder notificationBuilder)
	this.Manager.Notify(id, notificationBuilder.Build());

To test the notification, we have two options – one is to send a test notification via the Notification Hub, the other is to use Postman once again to create to trigger our Azure Function. In both cases, your result should be a notification on your device (after you deployed and run the application without the debugger being attached).



In this last post of the series, I showed you all steps that are needed to send out push notifications utilizing an Azure Notification Hub. It takes a bit of setup in the beginning, but the code involved is pretty easy and straight forward.

Now that the series is complete, you can have a look at the source code on Github. You need to add your own google-services.json file and your own keys as well to run the sample. As always, I hope this post, as well as this series, is helpful for some of you.

Until the next post, happy coding, everyone!
Posted by msicc in Android, Azure, Dev Stories, Xamarin, 1 comment
Use NuGets for your common Xamarin (Forms) code (and automate the creation process)

Use NuGets for your common Xamarin (Forms) code (and automate the creation process)

Internal libraries

Writing (or copy and pasting) the same code over and over again is one of those things I try to avoid when writing code. For quite some time, I already organize such code in libraries. Until last year, this required quite some work managing all libraries for each Xamarin platform I used. Luckily, the MSBuild SDK Extras extensions showed up and made everything a whole lot easier, especially after James Montemagno did a detailed explanation on how to get the most out of it for Xamarin plugins/libraries.

Getting started

Even if I repeat some of the steps of James’ post, I’ll start from scratch on the setup part here. I hope to make the whole process straight forward for everyone – that’s why I think it makes sense to show each and every step. Please make sure you are using the new .csproj type. If you need a refresh on that, you can check my post about migrating to it (if needed).


The first step is pulling in MSBuild.Sdk.Extras, which will enable us to target multiple platforms in one single library. For this, we need a global.json file in the solution folder. Right click on the solution name and select ‘Open Folder in File Explorer‘, then just add a new text file and name it appropriately.

The next step is to define the version of the MSBuild.SDK.Extras library we want to use. The current version is 1.6.65, so let’s define it in the file. Just click the ‘Solution and Folders‘ button to find the file in Visual Studio:

switch to folder view

Add these lines into the file and save it:

  "msbuild-sdks": {
    "MSBuild.Sdk.Extras": "1.6.65"

Modifying the project file

Switch back to the Solution view and right click on the .csproj file. Select ‘Edit [ProjectName].csproj‘. Let’s modify and add the project definitions. We’ll start right in the first line. Replace the first line to pull in the MSBuild.Sdk.Extras:

<Project Sdk="MSBuild.Sdk.Extras">

Next, we’re separating the Version tag. This will ensure that we’ll find it very quickly in future within the file:

  <!--separated for accessibility-->

Now we are enabling multiple targets, in this case our Xamarin platforms. Please note that there are two separated versions – one that includes UWP and one that does not. I thought I would be fine to remove the non-UWP one if I include UWP and was precent with some strange build errors that where resolved only by re-adding the deleted line. I do not remember the reason, but I made a comment in my template to not remove it – so let’s just keep it that way.

  <!--make it multi-platform library!-->
    <!--we are handling compile items ourselves below with a custom naming scheme-->
    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">netstandard2.0;MonoAndroid81;Xamarin.iOS10;uap10.0.16299;</TargetFrameworks>
    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netstandard2.0;MonoAndroid81;Xamarin.iOS10;</TargetFrameworks>

Now we will add some default NuGet packages into the project and make sure our file get included only on the correct platform. We follow a simple file naming scheme (Xamarin.Essentials uses the same):


This way, we are able to add all platform specific code together with the shared entry point in a single folder. Let’ start with shared items. These will be available on all platforms listed in the PropertyGroup above:

  <!--shared items-->
    <!--keeping this one ensures everything goes smooth-->
    <PackageReference Include="MSBuild.Sdk.Extras" Version="1.6.65" PrivateAssets="All" />

    <!--most commonly used (by me)-->
    <PackageReference Include="Xamarin.Forms" Version="" />
    <PackageReference Include="Xamarin.Essentials" Version="1.0.1" />

    <!--include content, exclude obj and bin folders-->
    <None Include="**\*.cs;**\*.xml;**\*.axml;**\*.png;**\*.xaml" Exclude="obj\**\*.*;bin\**\*.*;bin;obj" />
    <Compile Include="**\*.shared.cs" />

The ‘**\‘ part in the Include property of the Compile tag ensures MSBuild includes also classes in subfolders. Now let’s add some platform specific rules to the project:

  <ItemGroup Condition=" $(TargetFramework.StartsWith('netstandard')) ">
    <Compile Include="**\*.netstandard.cs" />

  <ItemGroup Condition=" $(TargetFramework.StartsWith('uap10.0')) ">
    <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.1.9" />
    <Compile Include="**\*.uwp.cs" />

  <ItemGroup Condition=" $(TargetFramework.StartsWith('MonoAndroid')) ">
    <!--need to reference all those libs to get latest minimum Android SDK version (requirement by Google)... #sigh-->
    <PackageReference Include="Xamarin.Android.Support.Annotations" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Compat" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Core.Utils" Version="" />
    <PackageReference Include="Xamarin.Android.Support.CustomTabs" Version="" />
    <PackageReference Include="Xamarin.Android.Support.v4" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Design" Version="" />
    <PackageReference Include="Xamarin.Android.Support.v7.AppCompat" Version="" />
    <PackageReference Include="Xamarin.Android.Support.v7.CardView" Version="" />
    <PackageReference Include="Xamarin.Android.Support.v7.Palette" Version="" />
    <PackageReference Include="Xamarin.Android.Support.v7.MediaRouter" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Core.UI" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Fragment" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Media.Compat" Version="" />
    <PackageReference Include="Xamarin.Android.Support.v7.RecyclerView" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Transition" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Vector.Drawable" Version="" />
    <PackageReference Include="Xamarin.Android.Support.Vector.Drawable" Version="" />
    <Compile Include="**\*.android.cs" />

  <ItemGroup Condition=" $(TargetFramework.StartsWith('Xamarin.iOS')) ">
    <Compile Include="**\*.ios.cs" />

Two side notes:

  • Do not reference version 6.2.2 of the Microsoft.NETCore.UniversalWindowsPlatform NuGet. There seems to be bug in there that will lead to rejection of your app from the Microsoft Store. Just keep 6.1.9 (for the moment).
  • You may not need all of the Xamarin.Android packages, but there are a bunch of dependencies between them and others, so I decided to keep them all

If you have followed along, hit the save button and close the .csproj file. Verifying everything went well is pretty easy – your solution structure should look like this:


Before we’ll have a look at the NuGet creation part of this post, let’s add some sample code. Just insert this into static partial classes with the appropriate naming scheme for every platform and edit the code to match the platform. The .shared version of this should be empty (for this sample).

     public static partial class Hello
        public static string Name { get; set; }

        public static string Platform { get; set; }

        public static  void Print()
            if (!string.IsNullOrEmpty(Name) && !string.IsNullOrEmpty(Platform))
                System.Diagnostics.Debug.WriteLine($"Hello {Name} from {Platform}");
                System.Diagnostics.Debug.WriteLine($"Hello unkown person from {Device.Android}");

Normally, this would be a Renderer or other platform specific code. You should get the idea.

Preparing NuGet package creation

We will now prepare our solution to automatically generate NuGet packages both for DEBUG and RELEASE configurations. Once the packages are created, we will push it to a local (or network) file folder, which serves as our local NuGet-Server. This will fit for most Indie-developers – which tend to not replicate a full blown enterprise infrastructure for their DevOps needs. I will also mention how you could push the packages to an internal NuGet server on a sideline (we are using a similar setup at work).

Adding NuGet Push configurations

One thing we want to make sure is that we are not going to push packages on every compilation of our library. That’s why we need to separate configurations. To add new configurations, open the Configuration Manager in Visual Studio:

In the Configuration Manager dialog, select the ‘<New…>‘ option from the ‘Active solution configuration‘ ComboBox:

Name the new config to fit your needs, I just use DebugNuget which will signal that we are pushing the NuGet package for distribution. I am copying the settings from the Debug configuration and let Visual Studio add the configurations to project files within the solution. Repeat the same for Release configuration.

The result should look like this:

Modifying the project file (again)

If you head over to your project file, you will see the Configurations tag has new entries:


Next, add the properties of your assembly and package:

    <!--assmebly properties-->

  <!--nuget package properties-->

    <PackageReleaseNotes>Xamarin Nugets sample package</PackageReleaseNotes>
    <PackageTags>xamarin, windows, ios, android, xamarin.forms, plugin</PackageTags>

    <Title>Xamarin Nugets</Title>
    <Summary>Xamarin Nugets sample package</Summary>
    <Description>Xamarin Nugets sample package</Description>

    <Owners>MSiccDev Software Development</Owners>
    <Authors>MSiccDev Software Development</Authors>
    <Copyright>MSiccDev Software Development</Copyright>

Configuration specific properties

Now we will add some configuration specific PropertyGroups that control if a package will be created.

Debug and DebugNuget

  <PropertyGroup Condition=" '$(Configuration)'=='Debug' ">
    <!--making this pre-release-->
    <!--needed for debugging!-->

  <PropertyGroup Condition=" '$(Configuration)'=='DebugNuget' ">
    <!--enable package creation-->
    <!--making this pre-release-->
    <!--needed for debugging!-->
    <!--this makes msbuild creating src folder inside the symbols package-->

The Debug configuration enables us to step into the Debug code while we are referencing the project directly during development, while the DebugNuget configuration will also generate a NuGet package including Source and Symbols. This is helpful once you find a bug in the NuGet package and allows us to step into this code also if we reference the NuGet instead of the project. Both configurations will add ‘-pre‘ to the version, making these packages only appear if you tick the ‘Include prerelease‘ CheckBox in the NuGet Package Manager.

Release and ReleaseNuget

  <PropertyGroup Condition=" '$(Configuration)'=='Release' ">

  <PropertyGroup Condition=" '$(Configuration)'=='ReleaseNuget' ">
    <!--enable package creation-->
    <!--include pdb for analytic services-->

The relase configuration goes well with less settings. We do not generate a separated symbols-package here, as the .pdb-file without the source will do well in most cases.

Adding Build Targets

We are close to finish our implementation already. Of course, we want to make sure we push only the latest packages. To ensure this, we are cleaning all generated NuGet packages before we build the project/solution:

  <!--cleaning older nugets-->
  <Target Name="CleanOldNupkg" BeforeTargets="Build">
      <FilesToDelete Include="$(ProjectDir)$(BaseOutputPath)$(Configuration)\$(AssemblyName).*.nupkg"></FilesToDelete>
    <Delete Files="@(FilesToDelete)" />
    <Message Text="Old nupkg in $(ProjectDir)$(BaseOutputPath)$(Configuration) deleted." Importance="High"></Message>

MSBuild provides a lot of options to configure. We are setting the BeforeTargets property of the target to Build, so once we Clean/Build/Rebuild, all old packages will be deleted by the Delete command. Finally, we are printing a message to confirm the deletion.

Pushing the packages

After completing all these steps above, we are ready to distribute our packages. In our case, we are copying the packages to a local folder with the Copy command.

  <!--pushing to local folder (or network path)-->
  <Target Name="PushDebug" AfterTargets="Pack" Condition="'$(Configuration)'=='DebugNuget'">
      <PackageToCopy Include="$(ProjectDir)$(BaseOutputPath)$(Configuration)\$(AssemblyName).*.symbols.nupkg"></PackageToCopy>
    <Copy SourceFiles="@(PackageToCopy)" DestinationFolder="C:\TempLocNuget" />
    <Message Text="Copied '@(PackageToCopy)' to local Nuget folder" Importance="High"></Message>

  <Target Name="PushRelease" AfterTargets="Pack" Condition="'$(Configuration)'=='ReleaseNuget'">
      <PackageToCopy Include="$(ProjectDir)$(BaseOutputPath)$(Configuration)\$(AssemblyName).*.nupkg"></PackageToCopy>
    <Copy SourceFiles="@(PackageToCopy)" DestinationFolder="C:\TempLocNuget" />
    <Message Text="Copied '@(PackageToCopy)' to local Nuget folder" Importance="High"></Message>

Please note that the local folder could be replaced by a network path. You have to ensure the availability of that path – which adds in some additional work if you choose this route.

If you’re running a full NuGet server (as often happens in Enterprise environments), you can push the packages with this command (instead of the Copy command):

<Exec Command="NuGet push "$(ProjectDir)$(BaseOutputPath)$(Configuration)\$(AssemblyName).*.symbols.nupkg" [YourPublishKey] -Source [YourNugetServerUrl]" />

The result

If we now select the DebugNuget/ReleaseNuget configuration, Visual Studio will create our NuGet package and push it to our Nuget folder/server:

Let’s have a look into the NuGet package as well. Open your file location defined above and search your package:

As you can see, the Copy command executed successfully. To inspect NuGet packages, you need the NuGet Package Explorer app. Once installed, just double click the package to view its contents. Your result should be similar to this for the DebugNuGet package:

As you can see, we have both the .pdb files as well as the source in our package as intended.


Even as an Indie developer, you can take advantage of the DevOps options provided with Visual Studio and MSBuild. The MSBuild.Sdk.Extras package enables us to maintain a multi-targeting package for our Xamarin(.Forms) code. The whole process needs some setup, but once you have performed the steps above, extending your libraries is just fast forward.

I planned to write this post for quite some time, and I am happy with doing it as my contribution to the #XamarinMonth (initiated by Luis Matos). As always, I hope this post is helpful for some of you. Feel free to clone and play with the full sample I uploaded on Github.

Until the next post, happy coding, everyone!

Helpful links:

Title image credit

P.S. Feel free to download the official app for my blog (that uses a lot of what I am blogging about):
iOS | Android | Windows 10

Posted by msicc in Azure, Dev Stories, iOS, UWP, Xamarin, 3 comments
Handle AtomicPay’s webhook with Microsoft Azure (Part 2/3) – invoice verification with Azure KeyVault

Handle AtomicPay’s webhook with Microsoft Azure (Part 2/3) – invoice verification with Azure KeyVault

Series overview

  1. Handle the incoming notification with an Azure Function (first post)
  2. Verify the invoice state within the Azure Function, but store the API credentials in the most secure way (this post)
  3. Send a push notification via Azure Notificationhub to all devices that have linked a merchant’s account to it (third post [coming soon])

Storing credentials securely

When we consume web services, we need to authenticate our applications against them/their API. In the past, I always saw (and in fact, I also made) samples that do ignore the security of those credentials and provide them in code, leaving additional research (if you are new to that topic) and making the samples incomplete. As the goal of this post is to verify the state of a received invoice against the AtomicPay API, the first step is to provide a secure mechanism for storing our API credentials on Azure.

Get your AtomicPay API keys

If you haven’t signed up for an AtomicPay account, you should probably do it now. Once you have logged in, open the menu and select ‘API Integration‘:

AtomicPay menu select API Integration

On this page, you find your pre-generated API-Keys. Should your keys be compromised, you will be able to regenerate your keys here as well:

AtomicPay API Integration page

Introducing Azure KeyVault

According to the Azure KeyVault documentation, it is

a tool for securely storing and accessing secrets. A secret is anything that you want to tightly control access to, such as API keys, passwords, or certificates. A Vault is logical group of secrets.

As we are dealing with a public/private key credential combo, Azure KeyVault fits our goal to securely store the credentials perfectly. Since November last year, Azure Functions are able to use the KeyVault via their AppSettings. This is what the first half of this post is about.

Creating a new KeyVault

Login to the Azure Portal and go to the Marketplace. Search for ‘Key Vault‘ there and select it from the results:

Azure Marketplace search for Key Vault

You will be prompted with the creation menu. Give it a unique name and select your existing resource group (which will make sure we are in the correct location automatically). Once done, click on the create button:

Azure create new key vault menu

It will take a minute or two until the deployment is done. From the notification, you’ll get a direct link to the resource:

In the overview menu, select ‘Secrets’, where we will store our credentials:

Azure KeyVault menu - select Secrets

If you are wondering why we are using the ‘Secrets‘ option over ‘Keys‘ – the keys are already generated by AtomicPay, and the import function wants a backup file. I did not have a deeper look into this option as the ‘Secrets‘ option offers all I need.

The next step is to add a secret entry for AtomicPay’s account id, public and private key:

Azure KeyVault add secret

Once you have added the Application ID and your keys into ‘Secrets‘, click on ‘Overview‘. On the right-hand side, you’ll see an entry called ‘DNS Name’. Hover with the mouse to reveal the copy button and copy it:

Azure KeyVault Url Copy

Now go to your Azure Function and select ‘Application settings‘. Scroll a bit down and add a new setting. You can name it whatever you want, I just used ‘KeyVaultUri‘. Paste the url you have copied earlier into the value field. Do not forget to hit the ‘Save‘-button after that:

Azure Function - Application settings

Now we are just one step away of being able to use the KeyVault in our code. Go back to ‘Overview‘ on your Function and click on the ‘Platform features‘ tab. Select ‘Identity‘ there:

Azure Function select Identity

We need to enable the ‘System assigned‘ managed identity feature to allow the Function to interact with the Azure KeyVault from our code. This will add our Function to an Azure AD instance that handles the access rights for us:

Azure function enable System assigned identity

Now we have everything in place to use the KeyVault to retrieve the API credentials we need for invoice verification.

Retrieving credentials in our code

Before we start to rewrite our function code, we need to install two NuGet-Packages into our Function project. Right click on the project and select ‘Manage NuGet Packages…‘. Search for these to packages and install them:

Refactoring the initial code

Whenever possible, we should take the chance to refactor our code. I have done so on adding the authentication layer for this sample. First, we will be moving the code to get the payload off the webhook into its own method:

        private static async Task<WebhookInvoiceInfo> GetPaymentPayload(HttpRequestMessage requestMessage)
            _traceWriter.Info("trying to get payload object from request...");
            WebhookInvoiceInfo result = null;
            _jsonSerializerSettings = new JsonSerializerSettings()
                MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
                DateParseHandling = DateParseHandling.None,
                Converters ={

                        new IsoDateTimeConverter { DateTimeStyles = DateTimeStyles.AssumeUniversal },

            _jsonSerializer = JsonSerializer.Create(_jsonSerializerSettings);

            using (var stream = await requestMessage.Content.ReadAsStreamAsync())
                using (var reader = new StreamReader(stream))
                    using (var jsonReader = new JsonTextReader(reader))
                        result = _jsonSerializer.Deserialize<WebhookInvoiceInfo>(jsonReader);

            return result;

Next, we need are going to write another method to retrieve the credentials from the Azure KeyVault and initialize the AtomicPay SDK properly:

        private static async Task<bool> InitAtomicPay()
            bool isAuthenticated = false;

            //initialize Azure Service Token Provider and authenticate this function against the KeyVault
            var serviceTokenProvider = new AzureServiceTokenProvider();
            var keyVaultClient = new KeyVaultClient(new KeyVaultClient.AuthenticationCallback(serviceTokenProvider.KeyVaultTokenCallback));

            //getting the key vault url
            var vaultBaseUrl = ConfigurationManager.AppSettings["KeyVaultUri"];

            //retrieving the appId and secrets
            var accId = await keyVaultClient.GetSecretAsync(vaultBaseUrl, "atomicpay-accId");
            var accPBK = await keyVaultClient.GetSecretAsync(vaultBaseUrl, "atomicpay-accPBK");
            var accPVK = await keyVaultClient.GetSecretAsync(vaultBaseUrl, "atomicpay-accPVK");

            //initialize AtomicPay SDK and return the result
            await AtomicPay.Config.Current.Init(accId.Value, accPBK.Value, accPVK.Value);

            if (!AtomicPay.Config.Current.IsInitialized)
                isAuthenticated = false;
                _traceWriter.Info("failed to authenticate with AtomicPay");
                isAuthenticated = true;
                _traceWriter.Info("successfully authenticated with AtomicPay.");

            return isAuthenticated;

Now that we authenticated against the API, we are finally able to verify the state of the invoice sent by the webhook. Let’s put everything together:

        //renamed this function (not particullary necessary)
        public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]HttpRequestMessage req, TraceWriter log)
            //enable other methods to write to log
            _traceWriter = log;
            _traceWriter.Info($"arrived at function trigger for 'InvoiceVerifier'...");

            //retrieving the payload
            var payload = await GetPaymentPayload(req);

            //if payload is null, there is something wrong
            if (payload != null)
                //authenticate the Function against AtomicPay
                var isAuthenticated = await InitAtomicPay();
                if (isAuthenticated)
                    AtomicPay.Entity.InvoiceInfoDetails invoiceInfoDetails = null;

                    _traceWriter.Info($"trying to verify invoice id {payload.InvoiceId} ...");

                    //verifying the invoice 
                    using (var atomicPayClient = new AtomicPay.AtomicPayClient())
                        var invoiceObj = await atomicPayClient.GetInvoiceByIdAsync(payload?.InvoiceId);

                        if (invoiceObj == null)
                            return req.CreateResponse(HttpStatusCode.BadRequest, $"there was an error getting invoice with id {payload?.InvoiceId}. Response was null");

                        if (invoiceObj.IsError)
                            return req.CreateResponse(HttpStatusCode.BadRequest, $"there was an error getting invoice with id {payload?.InvoiceId}. Message from AtomicPay: {invoiceObj.Value.Message}");
                            invoiceInfoDetails = invoiceObj.Value?.Result?.FirstOrDefault();

                    //this will be the point where we will trigger the push notification in the last part
                    switch (invoiceInfoDetails.Status)
                        case AtomicPay.Entity.InvoiceStatus.Paid:
                        case AtomicPay.Entity.InvoiceStatus.PaidAfterExpiry:
                        case AtomicPay.Entity.InvoiceStatus.Overpaid:
                        case AtomicPay.Entity.InvoiceStatus.Complete:
                            log.Info($"invoice with id {invoiceInfoDetails.InvoiceId} is paid");
                            log.Info($"invoice with id {invoiceInfoDetails.InvoiceId} is not yet paid");
                    req.CreateResponse(HttpStatusCode.Unauthorized, "failed to authenticate with AtomicPay");
                req.CreateResponse(HttpStatusCode.BadRequest, "there was an error getting the payload from request body");

            return req.CreateResponse(HttpStatusCode.OK, $"verified received invoice with id: '{payload?.InvoiceId}'");

Save the changes to your code. After that, right click on the project and hit ‘Publish’ to update the function on Azure. Once you have published the updated code, you should be able to test your Function once again with Postman and receive a result like this:

Postman response from updated function


As you can see, Microsoft Azure provides a convenient way to store credentials and use them in your Azure Functions. This approach makes the whole process a whole lot more secure. This post also showed the ease of implementation of the AtomicPay .NET SDK.

In the third and last post of this series, we will connect our function to an Azure Notificationhub for sending push notifications to all devices that have registered with a certain merchant account. As always, I hope also this post was helpful for some of you.

Until the next post, happy coding, everyone!

Title image credit

Posted by msicc in Azure, Crypto&Blockchain, Dev Stories, Xamarin, 0 comments
Handle AtomicPay’s webhook with Microsoft Azure (Part 1/3)

Handle AtomicPay’s webhook with Microsoft Azure (Part 1/3)

In case you missed the announcement of the SDK, here is a quick way to read it now:

What is a webhook?

Webhooks are gaining popularity, and a lot of services and websites provide them for easier interactions with other websites and service. Most commonly, webhooks are triggered by an event, and send a request to subscribers of the webhook. AtomicPay provides such a webhook for invoices and their payment state.

Why Azure?

There are several reasons, with Azure being my personal choice of cloud service being the main one. Besides that, Azure provides two additional features I am a fan of, namely Azure KeyVault for credential handling and Azure Notificationhub for pushing notifications to a broad range of platforms. This new series will be split into three parts:

  1. Handle the incoming notification with an Azure Function (this post)
  2. Verify the invoice state within the Azure Function, but store the API credentials in the most secure way (second post)
  3. Send a push notification via Azure Notificationhub to all devices that have linked a merchant’s account to it (third post)

Getting started

First, login to your Azure account (or create a new one). On the left menu, select ‘Create a resource’ and search for ‘Serverless Function App’:

Azure Portal create new resource

In the next step, you’ll assign a name for your Function, create a new resource group and assign or create a storage account:

Azure new Function App settings

Once deployment is finished, click the ‘Go to resource’ button in the portal notification:

Azure notification deployment succeeded

Next step is to add the code for our function. Click on the ‘+’ sign besides ‘Functions’:

add new function

Now you have to decide how you want to move on in development. I chose Visual Studio, because we need some Nuget packages later and I enjoy having Intellisense while writing code. Just follow the instructions on screen to get your project up and running.

select ide for writing function code

Make sure you are selecting the v1 (.NET Framework) version of the project. This is needed because we want to connect to a Notificationhub later (in the third post), and as of now, v2 does not support this (according to the docs).

VS new project dialog for Azure Function

With a click on ‘OK’, Visual Studio creates the new project for you.

Seeing some code… finally!

If you look at the just generated code in the generated Function class, you may immediately be reminded at something. You’re right, as Azure functions are based on ASP.NET, so there are some similarities. Let’s have a look at the parameters of the Run method (you can change the method name as the FunctionName attribute declares the method already as such).

The first parameter is the HttpTriggerAttribute, which defines the AuthorizationLevel, the allowed methods and an optional route. The only change that I made to the default attribute parameters is to remove the “get” method, because AtomicPay’s Webhook sends a POST request.

The second parameter is the HttpRequestMessage that contains the request sent from AtomicPay. If you have been working with APIs or other web requests already, this should be familiar. We will work with this part as the sample continues.

Last but not least, we have a logging provider that enables us to write to the Azure Function’s log (which can be really useful if you’re searching an error). We will also use this as the sample continues.

AtomicPay webhook payload

In order to be able to handle the payload from AtomicPay, it is helpful to have a payload sample. Luckily, AtomicPay provides a detailed documentation for the webhook (as it does for the API). The payload looks like this:


Depending on the cryptocurrency of the invoice, your function will be triggered multiple times – every time the status updates. As you probably want to have different actions for different states, it makes sense to create a class based on the JSON for deserialization and to further work with:

    public class WebhookInvoiceInfo
        public string InvoiceId { get; set; }

        public string OrderId { get; set; }

        public decimal FiatPrice { get; set; }

        public string FiatCurrency { get; set; }

        public string PaymentCurrency { get; set; }

        public string PaymentRate { get; set; }

        public string PaymentAddress { get; set; }

        public decimal PaymentTotal { get; set; }

        public decimal PaymentPaid { get; set; }

        public decimal PaymentDue { get; set; }

        public string PaymentTxid { get; set; }

        public long PaymentConfirmation { get; set; }

        public InvoiceStatus Status { get; set; }

        public InvoiceStatusException StatusException { get; set; }

You may have noticed that I have converters attached to some properties above. They are needed to convert the values into their correct types, as the API generally sends just strings. The class and its converters are part of the AtomicPay .NET SDK (find it on Nuget or Github), which we will use also in the second part of this blog series. Add the library in your prefered way to the project.

Working with the webhook’s payload

For this first part of the series, we are just going to write log entries based on the status of the incoming webhook. Just add these lines to the Run method of your function:

        public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]HttpRequestMessage req, TraceWriter log)
            log.Info($"arrived at function trigger for AtomicPay webhook.");
            log.Info("trying to get payload object from request...");
            WebhookInvoiceInfo result = null;
            _jsonSerializerSettings = new JsonSerializerSettings()
                MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
                DateParseHandling = DateParseHandling.None,
                Converters ={

                        new IsoDateTimeConverter { DateTimeStyles = DateTimeStyles.AssumeUniversal },

            _jsonSerializer = JsonSerializer.Create(_jsonSerializerSettings);

            using (var stream = await req.Content.ReadAsStreamAsync())
                using (var reader = new StreamReader(stream))
                    using (var jsonReader = new JsonTextReader(reader))
                        result = _jsonSerializer.Deserialize<WebhookInvoiceInfo>(jsonReader);

            if (result != null)
                log.Info($"received payload for invoice id: {result.InvoiceId} with status {result.Status.ToString()}");
                log.Info("there was an error getting the payload from the request body");

            return result == null ?
                req.CreateResponse(HttpStatusCode.BadRequest, "there was an error getting the payload from the request body") :
                req.CreateResponse(HttpStatusCode.OK, "OK");

We are reading the response content from the HttpRequestMessage and deserialize it. If there is no payload or something went wrong, our result will be null. We are writing a log entry that indicates if we have received a payload and the status of the invoice within it. In the end, we are returning the appropriate response to the POST request.

Testing the function locally

Another big advantage of using Visual Studio to write the Azure Function is the ability to debug locally. If you haven’t done so, you’ll need to install the
Azure Functions Core (CLI) tools – Visual Studio will prompt you to do so. Once that is done, we are able to debug locally:

Visual Studio debugging Azure function

Now that our local service is running, let’s test the function with Postman (this is one of my test invoices):

Postman request to local API test

As we can see, everything went smooth and our Function is working like expected:

API log local test

Now that we have verified our Function is able to run, we are ready to publish it.

Publishing the Function to Azure

To initiate the process, right click on the project name and select ‘Publish’. As we have already defined our project in the Azure Portal, we are using the ‘Select Existing’ option in the next step:

Publish to Azure Step 1

I am not selecting the ‘run from package file’ option here. Click ‘Publish’ to continue. You will be prompted with a selection window once again (you may have to login to your account first). Select your created project:

Publish to Azure Step 2

Confirm you selection with ‘OK’. After doing some additional preparation steps, Visual Studio will allow you to click the ‘Publish’ button:

Publish to Azure Step 3

Once you have published your function, visit the Azure Portal once again. Select your published function. The portal will show you the function.json declaration file. In the upper part of the website, you will find options to ‘Save‘, ‘Run‘ and ‘ </> Get function URL ‘. Click on the last one to view your function’s url:

Azure portal get function url

I am pretty sure you noticed the code parameter in the url. This parameter is needed with every call to your Azure function as authorization parameter. To test your function on Azure, copy the url and paste it into Postman (replacing the localhost url we used for local testing). You should get the same result in Postman – optimally, an OK-response.


If you followed along and your function is up and running – congratulations! You just created a basic “serverless” (aka running on someone else’s server) function. In the next post in this series, we will initialize the AtomicPay SDK properly, after we added our API credentials to another feature running on Azure – the KeyVault. As always, I hope this post is helpful for some of you.

Until the next post, happy coding, everyone!

Title image credit

Posted by msicc in Azure, Crypto&Blockchain, Dev Stories, Xamarin, 1 comment
Integrate crypto payments into your .Net applications with AtomicPay

Integrate crypto payments into your .Net applications with AtomicPay

If you have been following along, you may have noticed that I am discovering the cryptocurrency space lately. Today I want to introduce you to AtomicPay, a crypto payment processor that uses a different approach than traditional processors.

Why AtomicPay?

I have been thinking quite some time about how one can implement crypto payments into apps, be it desktop or mobile apps. Ever since then, it was clear for me that I need a solution where the payment happens between me and the customer directly, but all the infrastructure to handle invoicing etc. has to be handled from the outside.

Traditional payment processors often provide their service with a custodial wallet – you do not have control of the keys, so it is not really your wallet, just the grant to use it. Processing incoming transactions to this custodial wallet are routed through another wallet of the service, where those processors take their fees and process the reduced payment to your custodial wallet.

Security and Privacy

When it comes to crypto payments, there is always one problem: the balance between the ease of using and security/privacy. If you are looking at some other non-custodial services, they are providing payment processing by just using a single wallet address. Even if this is the easiest way to use crypto payments, it has some fundamental issues:

  • makes it way too easy to monitor transactions of a business/merchant entity
  • easy target for man-in-the-middle attacks
  • accountability issues (imagine 10 people paying the same amount, but for different products at nearly the same time)

Do you really want to put you and your customer/user at this risk? Surely not!

AtomicPay’s different approach

AtomicPay follows a different route. It provides an invoicing infrastructure that is easy to use, but payments are directly between merchant and customer.

It relies on the well established Electrum wallets. Never used any Electrum wallet before? No worries, AtomicPay helps you to initialize the wallet with step-by-step tutorials.

Electrum wallets are (optionally) SegWit-enabled, HD (hierarchical determistic) wallets. This means that for every incoming transcation, a new address is generated from your keys. Even though you could do multiple times, every address should be used only once. This makes attacks from the outside significantly harder and protects both you and your customer/user.

AtomicPay itself only has reading access – it can watch transactions, but never initialize any transfer out of the wallet of your funds. Atomicpay is able to calculate new valid receiver addresses for your Electrum wallet because of the BIP 0032 protocol by using your public key, which is the only thing you need to insert into their website.

AtomicPay features

AtomicPay provides quite a bunch of features:

  • on-the-fly PayUrl generation (QuickPay)
  • monitoring of incoming payments
  • notifications via Mail and Webhook
  • free-to-use REST API
  • very low fees
  • and more…

Introducing AtomicPay.Net SDK

As AtomicPay convinced me to be a valuable solution for crypto payments, I started to create a new library for their API. The SDK makes it very simple to call all endpoints and to integrate it into your .NET applications. The library is available on Github and as NuGet package. You’ll find informations on how to use the library on Github as well. My repo will also be forked into AtomicPay’s Github account soon and gain a bit more visibility this way.

What’s next?

The library is only the first step and lays the groundwork for more things to come, namely:

  • Webhook code sample with Azure Function and Notificationhub
  • Xamarin component for AtomicPay
  • Administration app for merchants (iOS and Android)

If you have ideas or questions on the library, feel free to ping me on the well known social accounts or leave a comment under this post. As always, I hope the library will be helpful.

Until the next post, happy coding, everyone!

Disclaimer: I am contributing to one or more crypto/blockchain projects with code written by me under the MIT License. Future contributions may contain their own (and different) disclaimer. I am not getting paid for my contributions to the project at the moment of writing this.

Please note that none of my crypto related posts is an investment or financial advice. As crypto currencies are volatile and risky,  you should only invest as much as you can afford to lose. Always do your own research!

Posted by msicc in Crypto&Blockchain, Dev Stories, 0 comments
2018 in review – Focus on Xamarin, RIP UniShare, the rise of crypto and blockchain

2018 in review – Focus on Xamarin, RIP UniShare, the rise of crypto and blockchain

This year, I had some rough time to keep me motivated on writing blog posts. In the early months, I was keeping my target to write about Xamarin Forms and my implementations, but I slowly lost pace around the summer.

Xamarin posts

Within the first half of the year, I was keeping a pretty constant 2 week frame for new blog posts, targeting Xamarin and Xamarin Forms. I touched several topics (some of which may be obsolete since Xamarin Forms 3.x). Here is a short recap:

The rise of crypto and blockchain

Since 2017, I was loosely following the area of crypto currencies and blockchain. This year, however, marks the beginning of a deeper dive into the blockchain area – and of course also into crypto currencies. I am not advising anyone to invest any money into crypto currencies, but there are certain projects out there that are really interesting. Two of them are social networks, similar to Tumblr: Steemit and Trybe. While Steemit is running on its own blockchain, Trybe is utilizing the EOS blockchain. Sadly, the .NET world seems to be widely ignored, so I stepped down a bit from posting on those two. I also tested several other networks running on or with blockchain, but none of them took me like the two mentioned above. If you want to learn more about the crypto currencies/projects I am interested in, just head over to my crypto page.

Open Source

Even if I did not made a lot of sound around it, I have worked on some libraries this year. I am not going into detail on every one, just head over to my Github:

I am currently working on another library (targetting crypto payments) – I will write about it once it is ready to be used in your projects.

RIP UniShare

One of the sadest moments this year was the death of UniShare, my most popular Windows (Phone) app. Long story short, due to some changes Facebook made to their API, I had to take UniShare to its funeral at the end of October. Read more about it here.

Looking forward to 2019

In 2019, I will continue my journey within the crypto/blockchain world. Like I wrote above, I am working on a crypto related project at the moment, which I hope to have ready in the early weeks of 2019. One of my other projects, WindowsUnited, will be taken over by another developer in 2019 (because he can invest more time into their official apps and work form them more ore less exclusively). This will free up some recsources, which I am trying to invest in my other projects and the rise of my blogging pace (again).

Thanks to all of you for reading my posts this year. I hope you’ll be with me in 2019 as well. I wish all of you a good arrival in 2019 and a happy new year once it arrives.

Until the next post, happy coding, everyone!

Posted by msicc in Crypto&Blockchain, Dev Stories, Editorials, 0 comments
Introducing Coinpaprika and announcing C# API Client

Introducing Coinpaprika and announcing C# API Client

As I am diving deeper and deeper into the world of cryptocurrencies, I am exploring quite some interesting products. One of them is Coinpaprika, a market research site with some extensive information on every coin they have listed.

What is Coinpaprika?

In the world of cryptocurrencies, there are several things one needs to discover before investing. Starting with information on the project and its digital currencies, the persons behind a project as well as their current value and its price, there is a lot of data to walk through before investing. Several sites out there are providing aggregated information, and even provide APIs for us developers. However, most of them are

  •  extremely rate limited
  •  freemium with a complex pricing model
  •  slow

Why Coinpaprika?

A lot of services that provide aggregated data rely on data of the big players like CoinMarketCap. Coinpaprika, however, has a different strategy. They are pulling their data from a whopping number of 176 exchanges into their own databases, without any proxy. They have their own valuation system and a very fast refreshing rate (16 000 price updates per minute). If you have some time and want to compare how prices match up with their competition, Coinpaprika even implemented a metrics page for you. In my personal experience, their data is more reliable average to those values I see on those exchanges I deal with (Binance, Coinbase, BitPanda, Changelly, Shapeshift).

Coinpaprika API and Clients

Early last week, I discovered Coinpaprika on Steemit. They announced their API is now available to the general public along with clients for PHP, GO, Swift and NodeJS. Coinpaprika has also a WordPress plugin and an embeddable widget (on a coin’s detail page) that allows you to easily show price information on your website. After discovering their site, I got in contact with them to discuss a possible C# implementation for several reasons:

  •  very generous rate limits (25 920 00 requests per month, others are around 6 000 to 10 000), which enables very different implementation scenarios
  •  their API is fast like hell
  •  their independence from third parties besides exchanges
  •  their very catchy name (just being honest)

A few days later, I was able to discuss the publication of the C# API client implementation I wrote with them. I am happy to announce that you can now download the C# API Client from Nuget or fork it from my Github repository. They will also link to it from their official API repository soon. The readme-file on Github serves as documentation as well and shows how to easily integrate their data into your .NET apps. The library itself is written in .NET Standard 2.0. If there is the need to target lower versions, feel free to open a pull request on Github. The Github repo contains also a console tester application.


If you need reliable market data and information on the different projects behind all those cryptocurrencies, you should evaluate Coinpaprika. They aggregate their data without any third party involved and provide an easy to use and blazing fast API. I hope my contribution in form of the C# API client will be helpful for some of you out there.

If you like their product as much as I do, follow them:

  • Twitter:
  • Facebook:
  • Steemit:
  • Medium:
  • Telegram:

Happy coding, everyone!

Disclaimer: I am contributing to this project with code written by me under the MIT License. Future contributions may contain their own (and different) disclaimer. I am not getting paid for my contributions to the project.

Please note that none of my crypto related posts is an investment or financial advice. As crypto currencies are volatile and risky,  you should only invest as much as you can afford to lose. Always do your own research!

Posted by msicc in Crypto&Blockchain, Dev Stories, Editorials, 1 comment
A faster way to add image assets to your Xamarin.iOS project in Visual Studio 2017

A faster way to add image assets to your Xamarin.iOS project in Visual Studio 2017

While Visual Studio has an editor that shall help to add new image assets to the project, it is pretty slow when adding a bunch of new images. If you have to add a lot of images to add, it even crashes once in while, which can be annoying. Because I was in the process of adding more than a hundred images for porting my first app ever from Windows Phone to iOS and Android, I searched for a faster way – and found it.

What’s going on under the hood?

When you add an imageset to your assets structure, Visual Studio does quite some work. These are the steps that are done:

  1. creation of a folder for the imageset in the Assets folder
  2. creation of a Contents.jsonfile
  3. modification of the Contents.json file
  4. modification of the .csproj file

This takes some time for every image, and Visual Studio seems to be quite busy with these steps. After analyzing the way imagesets get added, I immediately recognized that I am faster than Visual Studio if I do that work manually.

How to add the assets – step by step

  1. right click on the project in Solution Explorer and select ‘Open Folder in File Explorer‘ and find the ‘Assets‘ folder  open_folder_in_file_explorer
  2. create a new folder in this format: ‘[yourassetname].imageset
  3. add your image to the folder
  4. create a new file with the name Contents.json   add_image_and_contents_file
  5. open the file (I use Notepad++ for such operations) and add this minimum required jsonto it:
      "images": [
          "scale": "1x",
          "idiom": "universal",
          "filename": "[yourimage].png"
          "scale": "2x",
          "idiom": "universal",
          "filename": "[yourimage].png"
          "scale": "3x",
          "idiom": "universal",
          "filename": "[yourimage].png"
          "idiom": "universal"
      "properties": {
        "template-rendering-intent": ""
      "info": {
        "version": 1,
        "author": ""
  6. go back to Visual Studio, right click on the project again and select ‘Unload Projectunload_project
  7. right click again and select ‘Edit [yourprojectname].iOS.csproj‘ edit_ios_csproj
  8. find the ItemGroup with the Assets
  9. inside the ItemGroup, add your imageset with these two entries:
    <ImageAsset Include="Assets.xcassets\[yourassetname].imageset\[yourimage].png">
    <ImageAsset Include="Assets.xcassets\[yourassetname].imageset\Contents.json">
  10. close the file and reload the project by selecting it from the context menu in Solution Explorer

If you followed this steps, your assets should be visible immediately:

I did not measure the time exactly, but I felt I was significantly faster by adding all those images that way. Your mileage may vary, depending on the power of your dev machine.


Features like the AssetManager for iOS in Visual Studio are nice to have, but some have some serious performance problems (most of them are already known). By taking over the process manually, one can be a lot faster than a built-in feature. That said, like always, I hope this post is helpful for some of you.

Happy coding, everyone!

Posted by msicc in Dev Stories, iOS, Xamarin, 1 comment