mvvm

Xamarin Forms, the MVVMLight Toolkit and I (new series) [Updated]

Updated some code parts that needed to be changed in the ViewModelLocator.

Please see also this post for upgrading the project to .netStandard:

Xamarin Forms, the MVVMLight Toolkit and I: migrating the Forms project and MVVMLight to .NET Standard



Like some of you may have already registered, I have been doing the next step and went cross platform with my personal projects. I am primarily using Xamarin Forms, because I eventually like XAML a little too much. I took a break from round about 2 years on my Xamarin usage, and I am happy to see that it has improved a lot in the meantime. While Xamarin Forms still has room for improvementes, one can do already real and serious projects with it. As I like the lightweight MVVMLight toolkit as much as I like XAML, it was a no-brainer for me to start also my recent Xamarin projects with it.

There is quite some setup stuff to do if you want get everything working from the Xamarin Forms PCL, and this post will be the first in a series to explain the way I am currently using. Some of the things I do may be against good practice for Xamarin Forms, but sometimes one has to break out of them to write code more efficiently and also maintain it easier.

Installing MVVM Light into a Xamarin Forms PCL project

Of course, we will start with a new Xamarin Forms project. After selecting the type Cross Platform App in the New Project Dialog in Visual Studio, you’ll be presented with this screen, which was introduced in the Cycle 9 Release of Xamarin:

Select Xamarin Forms as UI Technology and PCL as Code Sharing Strategy to start the solution creation. As it creates several projects, this may take some time, so you may be able to refill your coffee cup in the meantime. Once the project is created, you’ll see 4 projects:

Before we are going to write some code, we will update and add the additional packages from within the NuGet Package Manager. If your are not targeting the Android versions 7.x , Xamarin Forms is not able to use the latest Android Support libraries, so you’ll have to stick with version 23.3.0 of them (see release notes of Xamarin Forms). Since it makes sense for a new app to target the newest Android version, we’ll be updating the Android Support packages for our sample app as well.

If the NuGet Package manager demands you to restart, you’ll better follow its advise. To verify everything is ok with the updated NuGet packages, set the Android project as Startup project and let Visual Studio compile it.

If all goes well, let’s make sure we are using the right UWP compiler version for Visual Studio 2015. The .NETCORE package for the UWP needs to be of Version 5.2.x, as 5.3 is only compatible with Visual Studio 2017.

Once the packages are up to date, we’ll finally download and install MVVMLight. As we will host all of our ViewModel Logic in Xamarin Forms, together with their Views, we just need to install it into the Portable library and into the UWP project:

There will be no changes to the project except adding the reference. We need to set up the structure ourselves. First, create two new folders, View and ViewModel:

Move the MainPage into the View Folder and adjust the Namespace accordingly. The next step is to setup a ViewModelLocator class, which takes a central part of our MVVM structure. Here is what you need for the base structure:

    public class ViewModelLocator
    {
        private static ViewModelLocator _instance;
        public static ViewModelLocator Instance => _instance ?? (_instance = new ViewModelLocator());

        public void Initialize()
        {
            ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
            RegisterServices();        

        }

        private static void RegisterServices()
        {
            //topic of another blog post
        }

        #region ViewModels  
        #endregion

        #region PageKeys
        #endregion
    }

You may notice some things. First, I am using the singleton pattern for the ViewModelLocator to make sure I have just one instance. I had some problems with multiple instances on Android, and using a singleton class helped to fix them. The second part of the fix is to move everything that is normally in the constructor into the Initialize() method. Now let’s go ahead, add a MainViewModel to the project and to the ViewModelLocator:

        public void Initialize()
        {
            ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
            RegisterServices();
            if (!SimpleIoc.Default.IsRegistered)
                SimpleIoc.Default.Register<MainViewModel>();
        }

        #region ViewModels
        public MainViewModel MainVm => ServiceLocator.Current.GetInstance<MainViewModel>();
        #endregion

Let’s give the MainViewModel just one property which is not subject to change (at least for now):

public string HelloWorldString { get; private set; } = "Hello from Xamarin Forms with MVVM Light";

The next step is to get the App.xaml file code right, it should look like this:

<?xml version="1.0" encoding="utf-8"?>
<Application xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             x:Class="XfMvvmLight.App" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             d1p1:Ignorable="d" 
             xmlns:d1p1="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:forms="http://xamarin.com/schemas/2014/forms" 
             xmlns:vm="clr-namespace:XfMvvmLight.ViewModel" >
  <Application.Resources>
    <!-- Application resource dictionary -->
    <forms:ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
      <vm:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />
    </forms:ResourceDictionary>
  </Application.Resources>
</Application>

Now that we have set up the baisc MVVM structure, we are going to connect our MainViewModel to our MainPage. There are two ways to do so.

In Xaml:

<ContentPage.BindingContext>
    <Binding Path="MainVm" Source="{StaticResource Locator}" />
</ContentPage.BindingContext>

in Code:

        public MainPage()
        {
            InitializeComponent();

            this.BindingContext = ViewModelLocator.Instance.MainVm;
        }

After that, just use the HelloWorldString property of the MainViewModel as Text in the already existing Label:

    <Label Text="{Binding HelloWorldString}"
           VerticalOptions="Center"
           HorizontalOptions="Center" />

Before we are able to test our code, we need to make sure our ViewModelLocator is initialized properly:

Android:

    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        protected override void OnCreate(Bundle bundle)
        {
            //TabLayoutResource = Resource.Layout.Tabbar;
            //ToolbarResource = Resource.Layout.Toolbar;

            base.OnCreate(bundle);

            global::Xamarin.Forms.Forms.Init(this, bundle);

            ViewModelLocator.Instance.Initialize();

            LoadApplication(new App());
        }
    }

iOS:

    [Register("AppDelegate")]
    public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
    {
        //
        // This method is invoked when the application has loaded and is ready to run. In this 
        // method you should instantiate the window, load the UI into it and then make the window
        // visible.
        //
        // You have 17 seconds to return from this method, or iOS will terminate your application.
        //
        public override bool FinishedLaunching(UIApplication app, NSDictionary options)
        {
            global::Xamarin.Forms.Forms.Init();

            ViewModelLocator.Instance.Initialize();

            LoadApplication(new App());

            return base.FinishedLaunching(app, options);
        }
    }

UWP:

//in App.xaml.cs:
        protected override void OnLaunched(LaunchActivatedEventArgs e)
        {

#if DEBUG
            if (System.Diagnostics.Debugger.IsAttached)
            {
                this.DebugSettings.EnableFrameRateCounter = true;
            }
#endif

            Frame rootFrame = Window.Current.Content as Frame;

            // Do not repeat app initialization when the Window already has content,
            // just ensure that the window is active
            if (rootFrame == null)
            {
                // Create a Frame to act as the navigation context and navigate to the first page
                rootFrame = new Frame();

                rootFrame.NavigationFailed += OnNavigationFailed;

                Xamarin.Forms.Forms.Init(e);

                ViewModelLocator.Instance.Initialize();

                if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
                {
                    //TODO: Load state from previously suspended application
                }

                // Place the frame in the current Window
                Window.Current.Content = rootFrame;
            }

            if (rootFrame.Content == null)
            {
                // When the navigation stack isn't restored navigate to the first page,
                // configuring the new page by passing required information as a navigation
                // parameter
                rootFrame.Navigate(typeof(MainPage), e.Arguments);
            }
            // Ensure the current window is active
            Window.Current.Activate();
        }

Let’s test our app on all platforms by building and deploying them:

Android

iOS Screenshot – post will be updated 

UWP

If you get the same screens, you are all set up to use Xamarin Forms with MVVMLight.

Conclusion

I know there are several specialized MVVM frameworks/toolkits floating around, which are commonly used for Xamarin Forms. As I am quite used to the MVVMLight toolkit, I prefer it over them. It is a lightweight solution, and I have more control over the code that is running than with the other options. I know I have to handle a lot of things in this case on my own (Navigation for example), but these will get their own blog posts. Starting with one of the future posts in this series, I will provide a sample app on my Github account.

If you have feedback or questions, feel free to get in contact with me via comments or on my social accounts. Otherwise, I hope this post and the following ones are helpful for some of you.

Happy coding, everyone!

Posted by msicc in Android, Dev Stories, iOS, Xamarin, 12 comments

Review of 2015–my first year in Switzerland

2015 was once again a year where a lot happened. My year began with the start of a new job – I am now employed as a full time developer at the Swiss Shareholder register ShareCommService AG. The first days in Switzerland where full of trouble, as I needed to start from scratch in a new country. I found a room in a shared appartment, which was quite ok for me alone. Internet, phone, insurance, pass port – these were the things I had to do in the first weeks besides learning all the new things that you usually do when entering a new company.

timerarmvvmAs part of my new job, it was also heavily demanded that I finally get deeply into MVVM. I always read a lot about that, but avoided it because I wanted to get things done in my private projects. My MVVM learning project was a WPF timer app that supports resuming, multiple timers and more. I learned it in the only right way: without any frameworks/toolkits, which helps a lot to understand what is going on. Needless to say that I am happy to be past this point, as we are using MVVM Light a lot in our LOB applications. LOB (Line-of-Business) applications are different from what I have done before. They are used only internally and directly affect our daily business. I also learned more about SQL and databases, and also SignalR took a big part of my learning curve.

I have the luck to learn from Roman Müller, who has a gigantic amount of experience in programming and also has always some funny programming story to tell from his past. Together with Reto, the second programmer in our team, he teached me a lot – not only programming things, but also better ways to analyze and think about situations where you can end in programming. I am really thankful to be part of this team. Our system administrator Stefan, which I like to refer as a ‘BOFH with the heart on the right place’, makes the team complete.

During the year, I participated also in several Annual General Meetings (AGM) of our customers. This was very helpful for me to understand my new job, as we are responsible for all things regarding the votings on their agenda.

My first private project this year was to rewrite Voices Admin as a universal (Windows 8.1) app. Of course I did it as plain MVVM app, and it helped me a lot to get even deeper into it, and also boosted my learning curve in my daily job. I updated my UserVoice library as well to be fully portable in the meantime. Currently, I am working on the UWP version of UniShare.

voices admin

My family stayed in Germany for several private reasons in the first month of the year. Beginning in August, we moved completely to Switzerland. I am happy that we passed this point as my family is very important to me and is giving me a lot of power. I have to thank my wife and also both of my kids for their understanding, as being a programmer is often very time consuming.

I also discovered a completely new area: the Internet of Things. With the Rasperry Pi2 supporting the Windows 10 IoT Core, I played around with it, learned a few new things about building hardware – and build a prototype for internal testings.

raspi2proto

You see, I had a year full of action, and I tried to make this post as short as possible. I am looking forward to 2016, where my developer story will continue. I did also blog only a few things this year, and I am trying to keep things up and post more frequently next year.

For now, I whish everyone all the best for the end of this year and also for 2016!

Posted by msicc in Editorials, 0 comments

How to implement a simple notification system in MVVM Windows 8.1 Universal apps

screenshot_07042015_152814

If your app performs actions, you most probably want to add also some confirmation if an action has finished. There are some ways to do this, like using local toast notifications or MessageDialogs. While I was working on Voices Admin v2, which is a universal app, I came along with a helper to simplify using local toast notifications. However, there came the point, where I got annoyed by the sound of these, and I looked into possible ways to replace them. My solution is a simple notification system, that uses the MVVM Light Messenger.

The first thing I did was adding a new property that broadcasts its PropertyChangedMessage to my ExtendedViewModelBase (which inherits from the MVVM Light ViewModelBase). This simplifies setting the notification text across multiple ViewModels as I don’t need to create a property in every ViewModel of my app:

public class ExtendedViewModelBase : ViewModelBase
    {
        public ExtendedViewModelBase()
        {
            
        }


        /// <summary>
        /// The <see cref="NotificationText" /> property's name.
        /// </summary>
        public const string NotificationTextPropertyName = "NotificationText";

        private string _notificationText = string.Empty;

        /// <summary>
        /// Sets and gets the NotificationText property.
        /// Changes to that property's value raise the PropertyChanged event. 
        /// This property's value is broadcasted by the MessengerInstance when it changes.
        /// </summary>
        public string NotificationText
        {
            get
            {
                return  _notificationText = string.Empty;
            }
            set
            {
                Set(() => NotificationText, ref _notificationText, value, true);
            }
        }
   }

The second step is to create the possibility to bind this into my view. I am using a custom PageBase class to simplify this. For those binding purposes it is common to add a DependencyProperty, and this is exactly what I did:

/// <summary>
        /// global property to bind the notification text against
        /// </summary>
        public static readonly DependencyProperty AppNotificationTextProperty = DependencyProperty.Register(
            "AppNotificationText", typeof (string), typeof (PageBase), new PropertyMetadata(string.Empty, (s, e) =>
            {
                var current = s as PageBase;

                if (current == null)
                {
                    return;
                }

                current.CheckifNotificationMessageIsNeeded(s);
            }));

        /// <summary>
        /// gets or sets the AppNotificationText
        /// </summary>
        public string AppNotificationText
        {
            get { return (string)GetValue(AppNotificationTextProperty); }
            set { SetValue(AppNotificationTextProperty, value); }}

You may have noticed that I hooked up into the PropertyChangedCallback of the DependecyProperty, which passes the execution to an separate method. Before we’ll have a look on that method, we need to add two private members to my PageBase: one for a StackPanel (mainly to set the Background color) and another one for Textblock. This is needed because this is the visible part of the notification. In the constructor of my PageBase class, I am filling them with live and connect them together:

            //instantiate and create StackPanel and TextBlock
            //you can put anything you want in the panel
            _panel = new StackPanel()
            {
                Background = new SolidColorBrush(Colors.Blue),
                Visibility = Visibility.Collapsed,
            };

            _textBlock = new TextBlock()
            {
                FontSize = 20,
                Margin = new Thickness(39, 10, 10, 10),
                TextAlignment = TextAlignment.Center
            };
            _panel.Children.Add(_textBlock);

The next thing we need to do is the FindChildren<T> helper method, which I took from the MSDN docs:

        /// <summary>
        /// Gets a list of DependencyObjects from the Visual Tree
        /// </summary>
        /// <typeparam name="T">the type of the desired object</typeparam>
        /// <param name="results">List of children</param>
        /// <param name="startNode">the DependencyObject to start the search with</param>
        public static void FindChildren<T>(List<T> results, DependencyObject startNode) where T : DependencyObject
        {
            int count = VisualTreeHelper.GetChildrenCount(startNode);
            for (int i = 0; i < count; i++)
            {
                var current = VisualTreeHelper.GetChild(startNode, i);
                if ((current.GetType()) == typeof(T) || (current.GetType().GetTypeInfo().IsSubclassOf(typeof(T))))
                {
                    T asType = (T)current;
                    results.Add(asType);
                }
                FindChildren<T>(results, current);
            }
         }

This helper enables us to find the top level grid, where we will add the StackPanel and control its visibilty and the TextBlock’s text. Which we are doing with the CheckifNotificationMessageIsNeeded() method:

        /// <summary>
        /// handles the visibility of the notification
        /// </summary>
        /// <param name="currentDependencyObject">the primary depenedency object to start with</param>
        private void CheckifNotificationMessageIsNeeded(DependencyObject currentDependencyObject)
        {
            if (currentDependencyObject == null) return;

            var children = new List<DependencyObject>();
            FindChildren(children, currentDependencyObject);
            if (children.Count == 0) return;

            var rootGrid = (Grid)children.FirstOrDefault(i => i.GetType() == typeof(Grid));

            if (rootGrid != null)

                if (!string.IsNullOrEmpty(AppNotificationText))
                {
                    if (!rootGrid.Children.Contains(_panel))
                    {
                        rootGrid.RowDefinitions.Add(new RowDefinition() {Height = new GridLength(_panel.ActualHeight, GridUnitType.Auto)});
                        _panel.SetValue(Grid.RowProperty, rootGrid.RowDefinitions.Count);

                        rootGrid.Children.Add(_panel);
                    }

                    _textBlock.Text = AppNotificationText;
                    _panel.Visibility = Visibility.Visible;
                }
                else if (string.IsNullOrEmpty(AppNotificationText))
                {
                    _textBlock.Text = string.Empty;
                    _panel.Visibility = Visibility.Collapsed;
                }
        }

Once we have the rootGrid on our Page, we are adding a new Row, set the StackPanel’s Grid.Row property to that and finally add the StackPanel to the Grid’s Children – but only if it does not exist already. No everytime the AppNotificationText property changes, the visibility of the StackPanel changes accordingly. Same counts for the TextBlock’s text. That’s all we need to do in the PageBase class.

The final bits of code we have to add are in the MainViewModel. I am using the MainViewModel as a kind of root ViewModel, which controls values and actions that are needed across multiple ViewModels. If you do not use it in the same way, you might need to write that code in all of your ViewModels where you want to use the notifications. The biggest advantage of my way is that the notification system (and other things) also works across pages.

The first thing we need is of course a property for the notification Text, which we will use to bind against on all pages where we want to use the notification system:

        /// <summary>
        /// The <see cref="GlobalNotificationText" /> property's name.
        /// </summary>
        public const string GlobalNotificationTextPropertyName = "GlobalNotificationText";

        private string _globalNotificationText = string.Empty;

        /// <summary>
        /// Sets and gets the GlobalNotificationText property.
        /// Changes to that property's value raise the PropertyChanged event. 
        /// </summary>
        public string GlobalNotificationText
        {
            get
            {
                return _globalNotificationText;
            }
            set
            {
                Set(() => GlobalNotificationText, ref _globalNotificationText, value);
            }
        }

Now we have this, we are hooking into the MVVM Messenger to catch the broadcasted NotificationText’s PropertyChangedMessage:

            Messenger.Default.Register<PropertyChangedMessage<string>>(this, message =>
            {
                if (message.PropertyName == ExtendedViewModelBase.NotificationTextPropertyName)
                {
                }
             });

If we would stop here, you would need to find a good point to set the NotificationText (and/or the GlobalNotificationText) property back to an empty string. This can be like the search a needle in the hay, believe me. That’s why I am giving every notification 5 seconds to be displayed, and the I am resetting the GlobalNotificationText  property in my MainViewModel automatically. To achieve this goal, I am using a simple DispatcherTimer with an Interval of 1 second:

            _notificationTimer = new DispatcherTimer() { Interval = new TimeSpan(0, 0, 1) };

DispatcherTimer has a Tick event, which fires every time a Tick happened. In our case, it fires every second. Hooking up into this event is essential, so add this line of code and let Visual Studio create the handler for you:

//in constructor:       
_notificationTimer.Tick += _notificationTimer_Tick;

//generated handler:
        private void _notificationTimer_Tick(object sender, object e)
        {
        }

Inside the Tick event handler, I am counting the ticks (using a private member in my MainViewModel). Once the timer passed 5 seconds, I am stopping the DispatcherTimer, reset the counter and finally set the GlobalNotificationText  property back to empty, which causes the notification to disappear:

            _notificationTimerElapsedSeconds++;

            if (_notificationTimerElapsedSeconds > 5)
            {
                _notificationTimer.Stop();
                _notificationTimerElapsedSeconds = 0;
                GlobalNotificationText = string.Empty;
            }

Of course we also need to start the DispatcherTimer. The perfect time for this is within the handler of the received PropertyChangedMessage we added earlier:

            //register for the global NotificationText PropertyChangedMessage from all VMs that derive from ExtendenViewModelBase
            Messenger.Default.Register<PropertyChangedMessage<string>>(this, message =>
            {
                if (message.PropertyName == ExtendedViewModelBase.NotificationTextPropertyName)
                {
                    if (!_notificationTimer.IsEnabled)
                    {
                        _notificationTimer.Start();
                    }
                    else
                    {
                        _notificationTimerElapsedSeconds = 0;
                    }

                    GlobalNotificationText = message.NewValue;
                }
            });

I am just checking if the DispatcherTimer is not yet enabled (= running) and start the timer in this case. If it is already running, I am just resetting my counter property to make sure that the notification is visible for 5 seconds again.

That’s it. Your MVVM (Light) app has now a simple and not so annoying notification system. It also provides the same experience across both platforms. There are sure ways to improve this here and there, that’s why I put up a sample to play around and contribute to on my Github account.

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

Happy coding!

Posted by msicc in Archive, 0 comments

How to implement a bindable progress indicator (loading dots) for MVVM Windows (8.1) Universal apps

Screenshot (23)

Now that I am on a good way to understand and use the MVVM pattern, I am also finding that there are some times rather simple solutions for every day problems. One of these problems is that we don’t have a global progress indicator for Windows Universal apps. That is a little bit annoying, and so I wrote my own solution. I don’t know if this is good or bad practice, but my solution is making it globally available in a Windows Universal app. The best thing is, you just need to bind to a Boolean property to use it. No Behaviors, just the one base implementation and Binding (Yes, I am a bit excited about it). For your convenience, I attached a demo project at the end of this post.

To get the main work for this done, we are implementing our own class, inherited from the Page class. The latter one is available for Windows as well as Windows Phone, so we can define it in the shared project of our Universal app. To do so, add a new class in the shared project. I named it PageBase (as it is quite common for this scenario, as I found out).

First, we need to inherit our class from the Page class:

public abstract class PageBase : Page

Now that we have done this, we need a global available property that we can bind to. We are using a DependencyProperty to achieve this goal. To make the property reflect our changes also to the UI, we also need to hook into a PropertyChanged callback on it:

        //this DepenedencyProperty is our Binding target to get all the action done!
        public static readonly DependencyProperty IsProgressIndicatorNeededProperty = DependencyProperty.Register(
            "IsProgressIndicatorNeeded", typeof (bool), typeof (PageBase), new PropertyMetadata((bool)false, OnIsProgressIndicatorNeededChanged));

        public static void OnIsProgressIndicatorNeededChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {

        }

        //get and send the value of our Binding target
        public bool IsProgressIndicatorNeeded
        {
            get { return (bool) GetValue(IsProgressIndicatorNeededProperty); }
            set { SetValue(IsProgressIndicatorNeededProperty, value); }
        }

The next step we need to do is to find the UIElement we want the progress indicator to be in. To do so, we are going through the VisualTree and pick our desired element. This helper method (taken from the MSDN documentation) will enable us to find this element:

        //helper method to find children in the visual tree (taken from MSDN documentation)
        private static void FindChildren<T>(List<T> results, DependencyObject startNode)
          where T : DependencyObject
        {
            int count = VisualTreeHelper.GetChildrenCount(startNode);
            for (int i = 0; i < count; i++)
            {
                var current = VisualTreeHelper.GetChild(startNode, i);
                if ((current.GetType()) == typeof(T) || (current.GetType().GetTypeInfo().IsSubclassOf(typeof(T))))
                {
                    T asType = (T)current;
                    results.Add(asType);
                }
                FindChildren<T>(results, current);
            }
        }

The method goes through the VisualTree, starting at the point we are throwing in as DependecyObject and gives us a List<T> with all specified Elements. From this List we are going to pick our UIElement that will hold the progress indicator for us. Let’s create a new method that will do all the work for us:

        private void CheckIfProgressIndicatorIsNeeded(DependencyObject currentObject)
        {
        }

Notice the DependencyObject parameter? This makes it easier for us to use the method in different places (which we will, more on that later). Let’s get our list of DependencyObjects from our parameter and pick the first Grid as our desired UIElement to hold the progress indicator:

            if (currentObject == null) return;

            //getting a list of all DependencyObjects in the visual tree
            var children = new List<DependencyObject>();
            FindChildren(children, currentObject);
            if (children.Count == 0) return;

            //getting a reference to the first Grid in the visual tree
            //this can be any other UIElement you define
            var rootGrid = (Grid)children.FirstOrDefault(i => i.GetType() == typeof(Grid));

Now that we have this, we are already at the point where we need to create our progress indicator object.  I declared a class member of type ProgressBar (which needs to be instantiated in the constructor then). This is how I set it up:

            //setting up the ProgressIndicator
            //you can also create a more complex object for this, like a StackPanel with a TextBlock and the ProgressIndicator in it
            _progressIndicator.IsIndeterminate = IsProgressIndicatorNeeded;
            _progressIndicator.Height = 20;
            _progressIndicator.VerticalAlignment = VerticalAlignment.Top;

The final step in the PageBase class is to check if there is already a chikd of type ProgressBar, if not adding it to the Grid and setting it’s Visibility property to Visible if our above attached DependencyProperty has the value ‘true’:

            //showing the ProgressIndicator
            if (IsProgressIndicatorNeeded)
            {
                //only add the ProgressIndicator if there isn't already one in the rootGrid
                if (!rootGrid.Children.Contains(_progressIndicator))
                {
                    rootGrid.Children.Add(_progressIndicator);
                }
                _progressIndicator.Visibility = Visibility.Visible;
            }

If the value is ‘false’, we are setting the Visibility back to collapsed:

            //hiding the ProgressIndicator
            else
            {
                if (rootGrid.Children.Contains(_progressIndicator))
                {
                    _progressIndicator.Visibility = Visibility.Collapsed;
                }
            }

Now that we have this method in place, let’s go back to our callback method we have been hooking into earlier. To reflect the changes that we are throwing into our DependencyProperty,  we are calling our method within the PropertyChanged callback. To do so, we are getting a reference to the PageBase class, which is needed because we are in a static method. Once we have this reference, we are calling our method to show/hide the progress indicator:

        public static void OnIsProgressIndicatorNeededChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            //resolving d as PageBase to enable us calling our helper method
            var currentObject = d as PageBase;

            //avoid NullReferenceException
            if (currentObject == null)
            {
                return;
            }
            //call our helper method
            currentObject.CheckIfProgressIndicatorIsNeeded(d);
        }

That’s all, we are already able to use the global progress indicator. To use this class, you need to do a few things. First, go to the code-behind part of your page. Make the class inherit from the PageBase class:

    public sealed partial class MainPage : PageBase

Now, let’s go to the XAML part and add a reference to your class:

    xmlns:common="using:MvvmUniversalProgressIndicator.Common"

Once you have done this, replace the ‘Page’ element with the PageBase class:

<common:PageBase>
//
</common:PageBase>

After you have build the project, you should be able to set the Binding to the IsProgressIndicatorNeeded property:

    IsProgressIndicatorNeeded="{Binding IsProgressIndicatorVisible}">

If you now add two buttons to the mix, binding their Commands to change the value of the Boolean property, you will see that you can switch the loading dots on and off like you wish. That makes it pretty easy to use it in a MVVM driven application.

But what if we need to show the progress indicator as soon as we are coming to the page? No worries, we are already prepared and need only a little more code for that. In the PageBase class constructor, register for the Loaded event:

            Loaded += PageBase_Loaded;

In the Loaded event, we are calling again our main method to show the progress indicator, but this time we use the current window content as reference to start with:

        void PageBase_Loaded(object sender, RoutedEventArgs e)
        {
            //using the DispatcherHelper of MvvmLight to get it running on the UI
            DispatcherHelper.CheckBeginInvokeOnUI(() =>
            {
                //Window.Current.Content is our visual root and contains all UIElements of a page
                var visualRoot = Window.Current.Content as DependencyObject;
                CheckIfProgressIndicatorIsNeeded(visualRoot);
            });

        }

As we need to reflect changes on the UI thread, I am using the DispatcherHelper of the MvvmLight Toolkit. You can use your own preferred method as well for that. That’s all, If you now test it with setting the IsProgressIndicatorNeeded property in your page directly to ‘True’ in XAML, you will see the loading dots right from the start.

Screenshot (21)

Like always, I hope this is helpful for some of you.

Happy coding!

Download Sample project

Posted by msicc in Archive, 1 comment

Helper class to easily display local toast notifications (Windows Universal app)

Often , we need to display a confirmation that some action in our app has been finished (like some data has been updated etc.). There are several ways of doing this, like displaying a MessageBox or MessageDialog. This however breaks the user interaction, and a lot of users will start complaining on that if your app keeps doing so. There needs to be a better way.

With the Coding4fun Toolkit floating around, you can mimic a toast notification – sadly only on Windows Phone (at least for the moment, but Dave told me he will work on implementing it for Windows, too). Also, Toastinet library is floating around, which is also able to mimic the toast notification behavior (although for Windows Universal app, the implementation is not that intuitive as for Windows  Phone). Both are fantastic libraries that I used in the past, but I wanted a solution that is implemented easily and works with my Universal app. So I did some searching in the Web and the MSDN docs, and found out that is pretty easy to use the system toast notifications on both platforms locally.

There are 8 possible ways to format toast notifications (as you can see here in the toast template catalog). This gives us pretty much options on how a notification can be styled. However, most options just work on Windows 8.1, while Windows Phone 8.1 apps will only show the notification in the way “app logo”  “bold text”  “normal text”. However, the notification system takes care of that, so you can specify some other type on Windows 8.1, while knowing that it gets converted on Windows Phone automatically. This allows us to write a helper class that implements all possible options without any headache.

the code parts for the notification

Let’s have a look at the code parts for the notification. First, you need to add two Namespaces to the class:

using Windows.Data.Xml.Dom;
using Windows.UI.Notifications;

After that, we can start writing our code. Toast notifications are formatted using Xml. Because of this, we need to get a reference to the underlying Xml template for the system toast notification:

ToastTemplateType xmlForToast= ToastTemplateType.ToastImageAndText01; 
XmlDocument toastXml = ToastNotificationManager.GetTemplateContent(xmlForToast);

System toast notifications can hold Text (and an Image on Windows 8.1). So we need to declare the elements of the toast notification. We are using the Xml methods of the DOM namespace to get the text elements of the chosen template first:

XmlNodeList toastTextElements = xmlForToast.GetElementsByTagName("text");
toastTextElements[0].AppendChild(xmlForToast.CreateTextNode("text1"));
//additional texts, depending on the template:
//toastTextElements[1].AppendChild(xmlForToast.CreateTextNode("text2"));
//toastTextElements[2].AppendChild(xmlForToast.CreateTextNode("text3"));

This is how the image element is implemented:

XmlNodeList toastImageElement = xmlForToast.GetElementsByTagName("image");
//setting the image source uri:
if (toastImageElement != null) ((XmlElement) toastImageElement[0]).SetAttribute("src", imageSourceUri);
//setting optional alternative text for the image
if (toastImageElement != null)  ((XmlElement) toastImageElement[0]).SetAttribute("alt", imageSourceAlternativeText);

You can attach local or remote images to the toast notification, but remember this works only on Windows, not on Windows Phone.

The next part we are able to set is the duration. The duration options are long (25 seconds) and short (7 seconds). The default is short, which should be ok for most scenarios. Microsoft recommends to use long only when a personal interaction of the user is needed (like in a chat). This is how we do it:

IXmlNode toastRoot = xmlForToast.SelectSingleNode("/toast");
((XmlElement) toastRoot).SetAttribute("duration", "short");

What we are doing here is to get the root element of the template’s Xml and add a new element for the duration. Now that we finally have set all options, we are able to create our toast notification and display it to the user:

ToastNotification notification = new ToastNotification(xmlForToast);
ToastNotificationManager.CreateToastNotifier().Show(notification);

the helper class

That’s all we need to do for our local notification. You might see that always rewriting the same code just makes a lot of work. Because the code for the toast notification can be called nearly everywhere in an app (it does not matter if you are calling it from a ViewModel or code behind), I wrote this helper class that makes it even more easy to use the system toast notification locally:

    public class LocalToastHelper
    {
        public void ShowLocalToast(ToastTemplateType templateType, string toastText01, string toastText02 = null, string toastText03 = null, string imageSourceUri = null, string imageSourceAlternativeText = null, ToastDuration duration = ToastDuration.Short)
        {
            XmlDocument xmlForToast = ToastNotificationManager.GetTemplateContent(templateType);
            XmlNodeList toastTextElements = xmlForToast.GetElementsByTagName("text");

            switch (templateType)
            {
                case ToastTemplateType.ToastText01:
                case ToastTemplateType.ToastImageAndText01:
                    toastTextElements[0].AppendChild(xmlForToast.CreateTextNode(toastText01));
                    break;
                case ToastTemplateType.ToastText02:
                case ToastTemplateType.ToastImageAndText02:
                    toastTextElements[0].AppendChild(xmlForToast.CreateTextNode(toastText01));
                    if (toastText02 != null)
                    {
                        toastTextElements[1].AppendChild(xmlForToast.CreateTextNode(toastText02));
                    }
                    else
                    {
                        throw new ArgumentNullException("toastText02 must not be null when using this template type");
                        
                    }
                    ;
                    break;
                case ToastTemplateType.ToastText03:
                case ToastTemplateType.ToastImageAndText03:
                    toastTextElements[0].AppendChild(xmlForToast.CreateTextNode(toastText01));
                    if (toastText02 != null)
                    {
                        toastTextElements[1].AppendChild(xmlForToast.CreateTextNode(toastText02));
                    }
                    else
                    {
                        throw new ArgumentNullException("toastText02 must not be null when using this template type");
                    }
                    ;
                    break;
                case ToastTemplateType.ToastText04:
                case ToastTemplateType.ToastImageAndText04:
                    toastTextElements[0].AppendChild(xmlForToast.CreateTextNode(toastText01));
                    if (toastText02 != null)
                    {
                        toastTextElements[1].AppendChild(xmlForToast.CreateTextNode(toastText02));
                    }
                    else
                    {
                        throw new ArgumentNullException("toastText02 must not be null when using this template type");
                    }
                    ;
                    if (toastText03 != null)
                    {
                        toastTextElements[2].AppendChild(xmlForToast.CreateTextNode(toastText03));
                    }
                    else
                    {
                        throw new ArgumentNullException("toastText03 must not be null when using this template type");
                    }
                    ;
                    break;
            }

            switch (templateType)
            {
                case ToastTemplateType.ToastImageAndText01:
                case ToastTemplateType.ToastImageAndText02:
                case ToastTemplateType.ToastImageAndText03:
                case ToastTemplateType.ToastImageAndText04:
                    if (!string.IsNullOrEmpty(imageSourceUri))
                    {
                        XmlNodeList toastImageElement = xmlForToast.GetElementsByTagName("image");
                        if (toastImageElement != null)
                            ((XmlElement) toastImageElement[0]).SetAttribute("src", imageSourceUri);
                    }
                    else
                    {
                        throw new ArgumentNullException(
                            "imageSourceUri must not be null when using this template type");
                    }
                    if (!string.IsNullOrEmpty(imageSourceUri) && !string.IsNullOrEmpty(imageSourceAlternativeText))
                    {
                        XmlNodeList toastImageElement = xmlForToast.GetElementsByTagName("image");
                        if (toastImageElement != null)
                            ((XmlElement) toastImageElement[0]).SetAttribute("alt", imageSourceAlternativeText);
                    }
                    break;
                default:
                    break;
            }

            IXmlNode toastRoot = xmlForToast.SelectSingleNode("/toast");
            ((XmlElement) toastRoot).SetAttribute("duration", duration.ToString().ToLowerInvariant());

            ToastNotification notification = new ToastNotification(xmlForToast);
            ToastNotificationManager.CreateToastNotifier().Show(notification);
        }

        public enum ToastDuration
        {
            Short,
            Long
        }
    }

As you can see, you just need to provide the wanted parameters to the ShowLocalToast method, which will do the rest of the work for you.

One word to the second switch statement I am using. The image element needs to be set only when we are using the ToastImageAndTextXX templates. There are three ways to implement the integration: using an if with 4  “or” options, the switch statement I am using or a string comparison with String.Contains. The switch statement is the cleanest option for me, so I decided to go this way. Feel free to use any of the other ways in your implementation.

In my implementation, I added also some possible ArgumentNullExceptions to make it easy to find any usage errors.

For your convenience, I attached the source file. Just swap out the namespace with yours. Download

The usage of the class is pretty simple:

var _toastHelper = new LocalToastHelper();
_toastHelper.ShowLocalToast(ToastTemplateType.ToastText02, "This is text 1", "This is text 2");

audio options

The system toasts have another option that can be set: the toast audio. This way, you can customize the appearance of the toast a bit more. I did not implement it yet, because there are some more options and things to remind, and I haven’t checked them out all together. Once I did, I will add a second post to this one with the new information.

As always, I hope this is helpful for some of you.

Happy coding!

Posted by msicc in Archive, 3 comments

How to easily check the pressed keyboard button with a converted event using MVVM (Windows Universal)

In case you missed it, I lately am deeply diving into MVVM. Earlier today, I wanted to implement the well loved feature that a search is performed by pressing the Enter button. Of course, this would be very easy to achieve in code behind using the KeyUpEvent (or the KeyDownEvent, if you prefer).

However, in MVVM, especially in a Universal app, this is a bit trickier. We need to route the event manually to our matching command. There are surely more ways to achieve it, but I decided to use the Behaviors SDK to achieve my goal. The first step is of course downloading the matching extension (if you haven’t done so before). To do so, click on TOOLS/Extensions and Updates in Visual Studio and install the Behaviors SDK from the list:image

The next step we need to do is to add a new Converter (I added it to the common folder, you may change this to your preferred place). As we are hooking up the KeyUpEventArgs, I called it KeyUpEventArgsConverter. After you created the class, implement the IValueConverter interface. You should now have a Convert and a ConvertBack method. We are just adding two lines of code to the Convert method:

            var args = (KeyRoutedEventArgs)value;
            return args;

That’s it for the Converter. Save the class and build the project. For the next step, we need to go to our View where the Converter should do its work. Before we can use it, we need to give our Converter a key to be identified by the Binding engine. You can do this app wide in App.xaml, or in your page:

<common:KeyUpEventArgsConverter x:Key="KeyUpEventArgsConverter"/>

Also, we need to add two more references to our View (besides the Common folder that holds our converter, that is):

    xmlns:i="using:Microsoft.Xaml.Interactivity" 
    xmlns:core="using:Microsoft.Xaml.Interactions.Core"

The next step is to implement the Behavior to our input control (a TextBox in my case):

<TextBox  Header="enter search terms" PlaceholderText="search terms" Text="{Binding KnowledgeBaseSearchTerms, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" >
    <i:Interaction.Behaviors>
         <core:EventTriggerBehavior EventName="KeyUp">
             <core:InvokeCommandAction
                   Command="{Binding SearchTermKeyEventArgsCommand}"
                   InputConverter="{StaticResource KeyUpEventArgsConverter}">
             </core:InvokeCommandAction>
          </core:EventTriggerBehavior>
     </i:Interaction.Behaviors>
</TextBox>

With the EventTriggerBehavior, we are able to hook into the desired event of a control. We then only need to bind to a Command in our ViewModel and tell the Behaviors SDK that it should route the “KeyUp” event using our Converter.

Let’s have a final look at the command that handles the event:

        public RelayCommand<KeyRoutedEventArgs> SearchTermKeyEventArgsCommand
        {
            get
            {
                return _searchTermKeyEventArgsCommand
                    ?? (_searchTermKeyEventArgsCommand = new RelayCommand<KeyRoutedEventArgs>(
                    p =>
                    {
                        if (p.Key == Windows.System.VirtualKey.Enter)
                        {
                            //your code here
                        }
                    }));
            }
        }

As you can see, we are using a Command that is able to take a Generic (in my case it comes from the MVVM Light Toolkit, but there are several other version floating around). Because of this, we are finally getting the KeyRoutedEventArgs into our ViewModel and are able to use its data and properties.

The VirtualKey Enumeration holds a reference to a lot of (if not all) keys and works for both hardware and virtual keyboards. This makes this code safe to use in an Universal app.

As I am quite new to MVVM, I am not entirely sure if this way is the “best” way, but it works as expected with little efforts. I hope this will be useful for some of you.

Useful links that helped me on my way to find this solution:

http://blog.galasoft.ch/posts/2014/01/using-the-eventargsconverter-in-mvvm-light-and-why-is-there-no-eventtocommand-in-the-windows-8-1-version/

https://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh868246.aspx

Happy coding, everyone!

Posted by msicc in Archive, 0 comments