Extending glidex.forms on Android to load a placeholder for images that fail to load

Extending glidex.forms on Android to load a placeholder for images that fail to load

What is glidex.forms?

The glidex.forms library is a Xamarin.Forms implementation of Glide, which is one of the quasi standards for imaging on Android (it is even recommended by Google). Luckily, Jonathan Peppers from Microsoft has a passion to improve Xamarin.Android, and Xamarin.Forms takes a big advantage from that as well. He made the Xamarin.Android Binding library as well as the Xamarin.Forms implementation. Like before with Xamarin.Forms.Nuke, I learned about that library because I am substituting my former image caching solution with Akavache.

Why do we need to extend the library?

If you want to load a placeholder that is stored in the resources of your Android project – there is no need. You could just implement a custom hook into the GlideExtensions class of glidex.forms (I’ll show you that one as well). But if you want to load an image from a Xamarin.Forms resource or even a from a font, we’ll need to extend the GlideExtensions class a little bit.

On a side note, I tried to use the existing mechanism of implementing an IGlideHandler for these purposes, but due to timing issues I never was able to load these kinds of placeholders and I moved on by extending the GlideExtensions class.

Show me some code!

Use Android resource

Let’s have a look at how to load an Android resource as a placeholder first (because it is the easiest way). To do so, we just need to create a custom implementation of an IGlideHandler in the Android project, which will then be called by the GlideExtensions implementation:

public class GlideWithAndroidResourcePlaceholder : IGlideHandler
    public GlideWithAndroidResourcePlaceholder()

    public bool Build(ImageView imageView, ImageSource source, RequestBuilder builder, CancellationToken token)
        if (builder != null)
            //easiest way - add the image to Android resources ....
            //general placeholder:

            //error placeholder:

            return true;
            return false;

As you can see, the RequestBuilder has already a placeholder mechanism in place. We just hook into that. If you want a general placeholder (shows the image also during download), use the Placeholder method. For failed image loading only, use the Error method. That’s it.

Use Xamarin.Forms resouce/FontImageSource

As we want to be able to load FontImageSource and Xamarin.Forms resources as well however, we need to go another route. Like we did on iOS, we need to add a placeholder property to the Forms class:

public static ImageSource? PlaceholderImageSource { get; private set; }

To fill our ImageSource with either a Xamarin.Forms resource or a FontImageSource, add these two methods as well:

public static void PlaceholderFromResource (string resourceName, Assembly assembly) =>
	PlaceholderImageSource = ImageSource.FromResource (resourceName, assembly);

public static void PlaceholderFromFontImageSource (FontImageSource fontImageSource) =>
	PlaceholderImageSource = fontImageSource;

Now that we have the PlaceholderImageSource in place, we need to extend the GlideExtensions class. First, we implement a Handler for FontImageSource. The Xamarin.Forms handler for FontImageSource provides us a bitmap, which we are going to use as a placeholder. I only got this working with the AsDrawable method, the AsBitmap method always threw an exception because it couldn’t cast the Bitmap to Drawable (I did not investigate that further).

private static async Task<RequestBuilder?> HandleFontImageSource (RequestManager request, Context? context, FontImageSource fontImageSource, CancellationToken token, Func<bool> cancelled)
	if (context == null)
		return null;

	var defaultHandler = new Xamarin.Forms.Platform.Android.FontImageSourceHandler ();

	var bitmap = await defaultHandler.LoadImageAsync (fontImageSource, context, token);

	if (token.IsCancellationRequested || cancelled())
		return null;

	if (bitmap == null)
		return null;

	return request.AsDrawable().Load (bitmap);

As for the HandleFontImageSource method, I also needed to change the return value of the HandleStreamImageSource method to use the AsDrawable method, otherwise we would get the same exception as with the FontImageSource:

static async Task<RequestBuilder?> HandleStreamImageSource (RequestManager request, StreamImageSource source, CancellationToken token, Func<bool> cancelled)
        //code omitted for readability

	return request.AsDrawable().Load (memoryStream.ToArray ());

The final steps to make it all work are done in the LoadViaGlide method. First, add another RequestBuilder? variable and name it errorBuilder:

RequestBuilder? errorBuilder = null;

After the switch that handles the source parameter, add these lines of code:

switch(Forms.PlaceholderImageSource) {
	case StreamImageSource streamSource:
		errorBuilder = await HandleStreamImageSource (request, streamSource, token, () => !IsActivityAlive (imageView, Forms.PlaceholderImageSource));
	case FontImageSource fontImageSource:
		errorBuilder = await HandleFontImageSource(request, imageView.Context, fontImageSource, token, () => !IsActivityAlive (imageView, Forms.PlaceholderImageSource));
		errorBuilder = null;

if (errorBuilder != null)
	builder?.Error (errorBuilder);

We are handling our PlaceholderImageSource like we do with the ImageSource that we intend to load. If we have a valid errorBuilder, we pass that into the entire process. With that, we have already everything in place. Let’s see how to use it in your app.

How to use it in your Xamarin.Forms – Android project

Head over to the MainActivity class in your Android project and add the following method:

private void AttachGlide()
    Android.Glide.Forms.Init(this, null, false);

    //recommended way of loading resource images=>
    //Android.Glide.Forms.Init(this, new GlideWithAndroidResourcePlaceholder(), false);

    //Xamarin Forms resource image
    //Android.Glide.Forms.PlaceholderFromResource("CachedImageTest.MSicc_Logo_Base_Blue_1024px_pad25.png", Assembly.GetAssembly(typeof(MainViewModel)));

    Android.Glide.Forms.PlaceholderFromFontImageSource(new FontImageSource
        Glyph = XfNativeCachedImages.Resources.MaterialDesignIcons.ImageBroken,
        FontFamily = "MaterialDesignIcons",
        Color = Xamarin.Forms.Color.Red

The Glide library needs to be initialized. Depending on the method you are using, there are separate ways to do so. The method above shows them all, you just need to change the commented code to play around with it in the sample (link at the end of the post). The mechanism is like the one I used for iOS and the Nuke package.

If you followed along (or downloaded the sample), you should see similar result to this:

Left: Single image with placeholder, Right: CollectionView placeholder


As we did on iOS, we now also use native caching and image handling on Android. It took me quite some time to get it up and running, but it was worth the effort. The sample has more than five hundred remote images loaded into a CollectionView. Check how smooth the scrolling is (even with DataBinding!).

You can find the sample here on Github, while the modified version of glidex.forms is available here. As always, I hope this post will be helpful for some of you.

Until the next post, happy coding, everyone!

Posted by msicc in Android, Dev Stories, Xamarin, 1 comment
Extending Xamarin.Forms.Nuke on iOS to load a placeholder for images that fail to load

Extending Xamarin.Forms.Nuke on iOS to load a placeholder for images that fail to load

What is Xamarin.Forms.Nuke?

Xamarin.Forms.Nuke is a Xamarin.Forms implementation of Nuke, one of the most advanced image libraries on iOS today. The Xamarin.Forms implementation focuses heavily on caching only, while the original library has a bunch of more features. I learned about this library when I started to look for an alternative to cache images via Akavache which I used before (I never blogged about that part because it wasn’t ready for that, tbh).

Why do we need to extend the library?

The library currently does only one thing (pretty well) – handling the caching of web images. It uses the default settings of the native Nuke library. The Xamarin.Forms implementation overwrites the ImageSourceHandler for UriImageSource and FileImageSource (optionally), but the case of placeholder loading is not intended in the original version. As I have multiple scenarios where a placeholder comes in handy, I decided to extend the library – and maintain my own fork of it from now on. (Maybe there will be a pull request to the original source, too).

Show me some code, finally!

For our extension, we modify the FormsHandler class as well as the ImageSourceHandler class. Let’s have a look at the FormsHandler class first. We are adding a new property for the placeholder:

public static ImageSource PlaceholderImageSource { get; private set; }

With that property in place, let’s add two methods. One method is for loading a placeholder image from an embedded resource file, while the second one is for specifying a FontImageSource.

public static void PlaceholderFromResource(string resourceName, Assembly assembly) =>
    PlaceholderImageSource = ImageSource.FromResource(resourceName, assembly);

public static void PlaceholderFromFontImageSource(FontImageSource fontImageSource) =>
    PlaceholderImageSource = fontImageSource;

I have chosen the FormsHandler class because setting the placeholder is a global thing (in my scenarios, your mileage may vary). That’s already everything in takes in the FormsHandler class, so let’s have a look at the ImageSourceHandler class.

As we are using the default Xamarin.Forms ImageSourceHandler for the resource image (which is a StreamImageSource) and the FontImageSource, we need to add the static fields for them first:

private static readonly StreamImagesourceHandler DefaultStreamImageSourceHandler = new StreamImagesourceHandler();

private static readonly FontImageSourceHandler DefaultFontImageSourcehandler = new FontImageSourceHandler();

Now let’s implement the loading of the placeholder in a separate method:

private static Task<UIImage> LoadPlaceholderAsync()
    switch (FormsHandler.PlaceholderImageSource)
        case StreamImageSource streamImageSource:
            FormsHandler.Warn($"loading placeholder from resource");
            return DefaultStreamImageSourceHandler.LoadImageAsync(streamImageSource);
        case FontImageSource fontImageSource:
            FormsHandler.Warn($"loading placeholder from Font");
            return DefaultFontImageSourcehandler.LoadImageAsync(fontImageSource);
            FormsHandler.Warn($"no valid placeholder found");
            return null;

As you can see, there is nothing overly complicated in this method. Based on the type of the placeholder set in the FormsHandler class, we are calling the default Xamarin.Forms implementation for the placeholder image. Let’s take this code into action by changing the LoadImageAsync method of the ImageSourceHandler:

public async Task<UIImage> LoadImageAsync(
    ImageSource imageSource,
    CancellationToken cancellationToken = new CancellationToken(),
    float scale = 1)
    var result = await NukeHelper.LoadViaNuke(imageSource, cancellationToken, scale);
    if (result == null)
        result = await LoadPlaceholderAsync();

    return result;

As we need to know if the Nukehelper class is able to load the image, we are already running the code by awaiting it at this level. If the result is null, we are loading the placeholder image via our prior implemented method. That’s all we need to do in our forked Xamarin.Forms.Nuke repository.

How to use it in your Xamarin.Forms – iOS project

First, clone my fork (or fork it if you want) of the Xamarin.Forms.Nuke repository and import it into your Xamarin.Forms solution and reference it in your iOS project. Once that is done, we need to initialize the Nuke library (like in the original source) in the AppDelegate‘s FinishedLaunching method:

Xamarin.Forms.Nuke.FormsHandler.Init(true, false);

The second step is to define the placeholder image source. The FontImageSource should be defined after the LoadApplication method. This way, you can the Xamarin.Forms way of loading the font as a resource.

//Resource image
Xamarin.Forms.Nuke.FormsHandler.PlaceholderFromResource("CachedImageTest.MSicc_Logo_Base_Blue_1024px_pad25.png", Assembly.GetAssembly(typeof(MainViewModel)));

Xamarin.Forms.Nuke.FormsHandler.PlaceholderFromFontImageSource(new FontImageSource
    Glyph = CachedImageTest.Resources.MaterialDesignIcons.ImageBroken,
    FontFamily = "MaterialDesignIcons",
    Color = Color.Red

Now use the Xamarin.Forms Image control like you always do. If the image from the web cannot be loaded, you will see the placeholder, like in these two examples:

cached image placeholder sample
Left: Single image failed loading, right image in CollectionView failed loading

With a few additions to the Xamarin.Forms.Nuke library, we have implemented a placeholder mechanism for images that can’t be loaded. As always, I hope this post will be useful for some of you. Now that I have the iOS implementation of a fast cached image with placeholder loading in place, I will turn to Android, where I will try to achieve the same using the Glidex.Forms library and extend it to load a placeholder. There will be a full sample once that is implemented as well. Stay tuned for that one!

Until the next post, happy coding, everyone!
Posted by msicc in Dev Stories, iOS, Xamarin, 2 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 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, 1 comment
WordPressReader (Standard) library is now available on Nuget

WordPressReader (Standard) library is now available on Nuget

I am happy to announce my new WordPressReader (Standard) library that is available on NuGet now. It is written in .netStandard 1.4 which enables you to use it in a lot of of places. As the name suggests, it focuses on reading tasks against the WordPress API.


  • get, search and filter posts
  • get pages
  • get and filter categories
  • get, search and filter tags
  • get comments
  • post anonymous comments (needs additional work on the WordPress site)
  • get basic user info

The library uses a generic WordPressEntity model implementation, which makes it easy to implement and extend. You can always get the raw json-value as well. The additional Error property on every model makes it easy to handle API errors properly. You can read the full documentation in the GitHub Wiki.

If you have problems with the library or want to contribute, you can do so on the GitHub repo.

Happy coding, everyone!

If you want to see the library in a live app, you can download my official blog reader app (which is written around it) here:

iOS  Android  Windows 10


Posted by msicc in Dev Stories, 2 comments