Category Archives: XAML

How to Draw a Diagonal Line Using Only XAML (and no path data)

I’ve been playing around with an app to maintain a score. The first thing that I wanted to do was to split the screen, but I wanted a diagonal split; similar to this:

phonescreen

There are a number of ways that this can be achieved; however, this is a method using only XAML. The same method will (I believe) work on Windows 8, WPF and Windows Phone.

First, split the screen into three rows or columns (which depends on how you want the orientation):

        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

This needs to be an odd number of rows / columns if you want the line to be central; additionally, an increased number of rows or columns will result in a smaller incline. Next, draw a transparent rectangle across the middle grid square:

        <Rectangle Name="Placeholder" Grid.Row="1" 
                   HorizontalAlignment="Stretch" VerticalAlignment="Stretch"
                   Opacity="0"/>

Finally, simply draw a line, binding the X2, Y2 values to the height and width of your rectangle:

        <Line Grid.Row="1" 
              X1="0" X2="{Binding ActualWidth, ElementName=Placeholder}"
              Y1="0" Y2="{Binding ActualHeight, ElementName=Placeholder}"
              StrokeThickness="2" Stroke="Blue"/>

Conclusion

I’m not saying the is the best, most efficient, or only way of doing this. However, it does mean that I can do it on both Windows Phone and Windows Store (and in WPF if I were so inclined) using a single shared project.

Startup Uri Not Working – Cannot locate recource ‘mainwindow.xaml’

I recently re-visited this project, and found that, amongst other things, it would no longer run up. Clearly something had changed, and it was a while until I realised what. The error I was getting was this:

Cannot locate resource

The App.Xaml looked like this:

<Application x:Class="TFSUtils.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:vm="clr-namespace:TFSUtils.ViewModel"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             StartupUri="MainWindow.xaml"
             mc:Ignorable="d">

Solution

I finally realised that I must have copied the MainWindow.Xaml into the Views folder as a last minute cleanup. The fix was very simple:

<Application x:Class="TFSUtils.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:vm="clr-namespace:TFSUtils.ViewModel"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             StartupUri="View/MainWindow.xaml"
             mc:Ignorable="d">

Conclusion

So, there you go: long untouched and untested code just spontaneously breaks! Magic.

Using a RepeatButton to Rapidly Increment Values

Recently, I’ve been playing with the WPF `RepeatButton`. I’ve not used it before, as it does seem to fulfil a very specific purpose. The use that I was trying to put it to was to act in the same way as you would expect your alarm clock to behave if you changed the time.

Say it’s currently 3:10 and you need it to be 3:15; you’d simply press the plus button five times, right? But what if you want it to be 17:50? Well, you’d hold the plus button down, but you wouldn’t expect it to increase by minutes; you’d maybe expect it to jump by 30 mins at a time after holding the plus button for a while.

The RepeatButton can do the same… but unfortunately not out of the box.

The Box

What you can do out of the box is this:

 <RepeatButton Content="+" Name="IncreaseButton"/>

And to handle the click:

IncreaseButton.Click += new RoutedEventHandler(IncreaseButton_Click);

Finally:

private void IncreaseButton_Click(object sender, RoutedEventArgs e)
{            
    Value += 1;
}

What’s wrong with that?

So far, so good, but what if I want the increment to increase though, as described in the alarm clock scenario above? I have two options here. One thing you can do is to increase the frequency that you increment; however, what I wanted to do was to increase the increment. The way I did it was to store a count:

private int _incrementButtonRepeat;

Then, in the `click` event:

private void IncreaseButton_Click(object sender, RoutedEventArgs e)
{            
    if (_incrementButtonRepeat > 5)
        Value += 5;
    else
        Value += 1;
    _incrementButtonRepeat++;        
}

Finally, you’ll need to reset:

private void IncreaseButton_PreviewMouseUp(object sender, MouseButtonEventArgs e)
{
    _incrementButtonRepeat = 0;
}

A little gotcha here is the MouseUp command never seems to fire, because it’s apparently handled internally. Use the preview to intercept it first.

Conclusion

You could create a very basic control that encapsulates this behaviour, based on some parameters; then you’d never have to consider this again.

Creating a Shared Project in WPF

The new thing for VS 2013 is Universal Apps. They allow you to create a Win 8 and Phone app with shared code. But what if you’re writing LOB apps in WPF, maybe using MVVM? You may have a Winforms app and a XAML app, and want to share code; or have two WPF apps that share a core code base, and some screens.

This post walks through creating a sample shared app.

Create WPF App

I’ll just cover WPF in this post. Start by creating a new application:

sharedcode1

Okay, so we have a WPF application (as you might already have). How to create a shared project? Well, the bad news is: you can’t; at least as far as I’m aware (please, please, please let me know in the comments if you know this to be false!).

So, if you can’t create a shared application without a universal one then create a universal one in the same solution:

sharedcode2

This creates a shared app with a reference from Windows 8.1 and Windows Phone 8.1:

sharedcode3

Now, what comes next might feel like a hack… and there’s a good reason for that!

Have a look in the Win 8 app csproj:

sharedcode4

Copy this into the csproj file of the WPF project (remember the path may be different – although in this case, are not):

sharedcode6

The important thing here is the `Label`. However, you’re most likely to get the path wrong. If you do then when you update the project in VS it will fail to load and give you an error message telling you where it’s trying to find the shared project. Having done this a couple of times, my advice is have this error message up, and try to navigate to the path in Windows Explorer: you should see where you went wrong quickly enough.

Adding stuff to the shared project

Start by adding a page to the shared project so that we can see that it works:

sharedcode7

Make it obvious so that you can recognise it:

sharedcode8

Okay, so you’ve now created a shared project, added some shared content, and referenced it from your main project. Next, tidy up by removing Windows 8 and Phone 8 apps and add a second WPF app:

sharedcode9

To make sure that this is, in fact, a shared project, create and make the same change to the second project and then modify each to call the shared page; e.g.:

    private void Button_Click(object sender, RoutedEventArgs e)
        {
            TestPage test = new TestPage();
            Window w = new Window();
            w.Content = test;
            w.Show();

        }

Then run both projects:

sharedcode10

Notes, and using this in an MVVM architecture

Okay – some things that are worth noting here. The main thing is this: the shared code is just that – shared. If you call something like:

typeof(TestPage).Assembly

You will get the assembly of the running application. Effectively, you’ve created a kind of link between the projects, without the messiness of actually creating a link. The consequences of this are that you must ensure that code in the shared project only has dependencies that can be resolved in ALL the projects that include the shared project.

MVVMCross

I’ve tried this on MVVM Cross using two projects and sharing XAML files; and it works. MVVM Cross looks in the current assembly for a `MyView`, when you navigate to a `MyViewModel`. It will find it providing all your projects reference the shared project and you do not try to re-implement the view.

To clarify:

– Creating a shared project between Winforms and WPF that shares a XAML file will most probably not work (admittedly I haven’t tried it).

– Creating a shared project for two WPF projects and copying MyView.xaml into the shared project, leaving the original intact will cause MVVM Cross to fail to resolve the page (because it doesn’t know which one you want).

Automatically focus on the newest item in a ListView using WinRT, MVVM and Behaviors SDK

The Behaviors SDK was introduced recently for WinRT. Here’s how you could use it to add functionality to a Listview to scroll to the newest item.

ListView

To start with, here’s the listview XAML:

            <ListView ItemsSource="{Binding DataLog}" x:Name="StatusUpdate">                
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding}" />
                    </DataTemplate>
                </ListView.ItemTemplate>

            </ListView>

And here’s the ViewModel that updates it:

        private void UpdateStatusLog(string msg)
        {
            Log.Add(msg);
        }

If you add to the listview, what you should notice is that once you’ve filled it, you’ll start to add items off the bottom.

Behaviors (sic)

The Behaviors SDK is now available for WinRT. Once you’ve included it in your project, you get a number of build in behaviours and, you can create your own. Before you build your own, a base class will probably make you feel more at home (Reference):

    public abstract class Behaviour<T> : DependencyObject, IBehavior where T : DependencyObject
    {

        [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
        public T AssociatedObject { get; set; }

        protected virtual void OnAttached()
        {
        }

        protected virtual void OnDetaching()
        {
        }

        public void Attach(Windows.UI.Xaml.DependencyObject associatedObject)
        {
            this.AssociatedObject = (T)associatedObject;
            OnAttached();
        }

        public void Detach()
        {
            OnDetaching();
        }

        DependencyObject IBehavior.AssociatedObject
        {
            get { return this.AssociatedObject; }
        }
    }

Not least, because you can correct the spelling of Behaviour 🙂

ListView Behaviour

    public sealed class AutoScrollToLastItemBehavior : Behaviour<ListView>
    {
        // Need to track whether we've attached to the collection changed event
        bool _collectionChangedSubscribed = false;

        protected override void OnAttached()
        {
            base.OnAttached();
            AssociatedObject.SelectionChanged += SelectionChanged;

            // The ItemSource of the listView will not be set yet, 
            // so get a method that we can hook up to later
            AssociatedObject.DataContextChanged += DataContextChanged;
        }

        private void SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            ScrollIntoView();
        }

        private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            ScrollIntoView();
        }

        private void DataContextChanged(FrameworkElement sender, DataContextChangedEventArgs args)
        {
            // The ObservableCollection implements the INotifyCollectionChanged interface
            // However, if this is bound to something that doesn't then just don't hook the event
            var collection = AssociatedObject.ItemsSource as INotifyCollectionChanged;
            if (collection != null && !_collectionChangedSubscribed)
            {
                // The data context has been changed, so now hook 
                // into the collection changed event
                collection.CollectionChanged += CollectionChanged;
                _collectionChangedSubscribed = true;
            }

        }

        private void ScrollIntoView()
        {
            int count = AssociatedObject.Items.Count;
            if (count > 0)
            {
                var last = AssociatedObject.Items[count - 1];
                AssociatedObject.ScrollIntoView(last);
            }
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            AssociatedObject.SelectionChanged -= SelectionChanged;
            AssociatedObject.DataContextChanged -= DataContextChanged;

            // Detach from the collection changed event
            var collection = AssociatedObject.ItemsSource as INotifyCollectionChanged;
            if (collection != null && _collectionChangedSubscribed)
            {
                collection.CollectionChanged -= CollectionChanged;
                _collectionChangedSubscribed = false;

            }
        }

Attaching the behaviour

Finally, change the listview to include a call to the behaviour:

            <ListView ItemsSource="{Binding Log}" x:Name="StatusUpdate">                
                <i:Interaction.Behaviors>
                    <behaviours:AutoScrollToLastItemBehavior />
                </i:Interaction.Behaviors>
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding}"/>
                    </DataTemplate>
                </ListView.ItemTemplate>

            </ListView>

Also, you need to reference Interactivity, and your behaviours:

    xmlns:behaviours="using:KingMaker.Behaviours"    
    xmlns:i="using:Microsoft.Xaml.Interactivity" 

The listview should now behave as expected.

Creating and Binding to a User Control in MVVM Cross

While creating my game, I recently came across the problem of navigation. This post describes how to create a custom user control and react to the event inside.

The usual disclaimer still applies here; although this is an MVVM Cross post, the contents of it should be applicable for any MVVM Framework or, in fact, any XAML binding at all.

User Control

The user control that I’m going to use is simply a navigation bar to appear at the top of each screen.

The XAML for the user control is here:

<UserControl
    x:Name="NavigationControlRoot">
    
    <Grid DataContext="{Binding ElementName=NavigationControlRoot}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <Button Content="Home" Grid.Column="0" Command="{Binding HomeClick}" />
        <Button Content="Back" Grid.Column="1" Command="{Binding BackClick}" />
    </Grid>
</UserControl>

So, I’ve got two commands, binding to the code behind. The key point here is that the root control (grid) binds to the DataContext of the user control – effectively this binds it to the containing DataContext. Here’s the code behind:

    public sealed partial class NavigationPanel : UserControl
    {
        public static DependencyProperty BackCommandProperty =
            DependencyProperty.Register(
                "BackClick",
                typeof(ICommand),
                typeof(NavigationPanel),
                new PropertyMetadata(null));

        public static DependencyProperty HomeCommandProperty =
            DependencyProperty.Register(
                "HomeClick",
                typeof(ICommand),
                typeof(NavigationPanel),
                new PropertyMetadata(null));

        public NavigationPanel()
        {
            this.InitializeComponent();
        }
        
        public ICommand BackClick
        {
            get
            {
                return (ICommand)GetValue(BackCommandProperty);
            }

            set
            {
                SetValue(BackCommandProperty, value);
            }
        }

        public ICommand HomeClick
        {
            get
            {
                return (ICommand)GetValue(HomeCommandProperty);
            }

            set
            {
                SetValue(HomeCommandProperty, value);
            }
        }        
    }

So, you’ve now exposed two dependency properties and bound them to the XAML in the user control.

Host App

Here’s the relevant XAML for the hosting view:

<controls:NavigationPanel BackClick="{Binding BackClickCommand}"                                  
                                  HomeClick="{Binding HomeClickCommand}"/>

And that just binds to the ViewModel as you would expect.

        private IMvxCommand _homeClickCommand;
        public IMvxCommand HomeClickCommand
        {
            get
            {
                if (_homeClickCommand == null)
                {
                    _homeClickCommand = new MvxCommand(() => GoHome());
                }
                return _homeClickCommand;
            }
            set
            {
                _homeClickCommand = value;
            }
        }

        private void GoHome()
        {
            ShowViewModel<MainViewModel>();
        }

For me, this is in a base view model, so it responds to the same command in every view.

Conclusion

I think the final version of this code will interact with an IMvxPresenter in some way, which may make another post.

Updating a View Model from Inside a Collection

My last post suggested a concept of having a `Selectable` Model, which effectively wraps a model in a class with a generic item and an `IsSelected` property. This does, however, present a slight issue. What if you want to update the view model, based on the item being selected, or de-selected?

Say, for example, that from my previous post, you had a property on the Person class called Wages, and wanted to display the total wages of all the selected people. You would have defined `TotalCostSummary` in the ViewModel, and bound it in the View.

My solution is to pass a delegate into the Selectable item. Here’s how I did it (this doesn’t really make any sense without referring back to the first post).

SelectableItem Model

In the `SelectableItem`, define a new property like so:

        private Action _updateMethod = null;
        public Action IsSelectedChangedMethod
        {
            get { return _updateMethod; }
            set
            {
                _updateMethod = value;
            }
        }

And change `IsSelected` to looks like this:

        private bool _isSelected;
        public bool IsSelected
        {
            get { return _isSelected; }
            set
            {
                _isSelected = value;                
                RaisePropertyChanged();
                
                if (_updateMethod != null)
                    _updateMethod();
            }
        }

ViewModel

        private void UpdateTotalCost()
        {
            _summary = SelectablePeople.Where(a => a.IsSelected).Sum(s => s.Item.Wages);
            RaisePropertyChanged(() => TotalCostSummary);
        }

Next, change the code to define the list:

List<Person> population = GetPeople();
SelectablePeople = new ObservableCollection<SelectableItem<Person>>(population
	.Select(n => new SelectableItem<Person>() 
	{ 
		Item = n, IsSelected = false, IsSelectedChangedMethod = (() => UpdateTotalCost())  
	}).ToList());

Conclusion

The net effect is that the changes now made inside the model can bubble up to the ViewModel, but the separation of the two has been maintained.

Binding IsSelected Method in the ListView Control in WinRT

Basically, it’s not possible. However, this is the best (and only that works) workaround that I found.

Subclass the Listview

I tried everything. Absolutely everything.

I tried straightforward binding – that doesn’t work for IsSelected.
I tried using WinRT Xaml Toolkit – didn’t work.
I tried using Setters – they don’t work for WinRT.

Finally, I came across this solution; here’s the listview subclass (stolen directly from here: http://stackoverflow.com/questions/15994021/listviewitem-isselected-binding-works-for-wpf-but-not-for-winrt):

    public class ListViewEx : ListView
    {
        protected override void PrepareContainerForItemOverride(Windows.UI.Xaml.DependencyObject element, object item)
        {
            base.PrepareContainerForItemOverride(element, item);
            
            ListViewItem listItem = element as ListViewItem;
            Binding binding = new Binding();
            binding.Mode = BindingMode.TwoWay;
            binding.Source = item;
            binding.Path = new PropertyPath("IsSelected");
            listItem.SetBinding(ListViewItem.IsSelectedProperty, binding);
        }
    }

Obviously this does restrict the IsSelected property name. My class looks something like this:

    public class Person
    {
        public string Name { get; set; }
        …
    }

I didn’t want to add an IsSelected property to this; because it doesn’t directly relate to the entity. My solution was to wrap this inside a class such as this:

    public class SelectableItem<T> : INotifyPropertyChanged
    {
        private T _item;
        public T Item 
        {
            get { return _item; }
            set
            {
                _item = value;
                RaisePropertyChanged();
            }
        }

        private bool _isSelected;
        public bool IsSelected
        {
            get { return _isSelected; }
            set
            {
                _isSelected = value;                
                RaisePropertyChanged();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void RaisePropertyChanged([CallerMemberName] string name = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(name));
            }
        }
}

And build it like this:

                List<Person> population = GetPeople();
                SelectablePeople = new ObservableCollection<SelectableItem<Person>>(population
                    .Select(n => new SelectableItem<Person>() { Item = n, IsSelected = false }).ToList());

So, finally, bind the collection to the new subclassed listview like this:

        <controls:ListViewEx x:Name="ItemListView" Grid.Column="0" Grid.Row="1"
                        ItemsSource="{Binding SelectablePeople}"                        
                        SelectionMode="Multiple"                        
                        Width="Auto" Height="Auto" >

            <controls:ListViewEx.ItemTemplate>
                <DataTemplate x:Name="MyTemplate">
                    <StackPanel Orientation="Horizontal">
                        <TextBlock                            
                            Text="{Binding Item.Name}"/>
                    </StackPanel>
                </DataTemplate>
            </controls:ListViewEx.ItemTemplate>

        </controls:ListViewEx>

MVVMCross – ShowViewModel not working?

I thought I’d jot this down, as it had me for a short while. Imagine that you have a line of code that looks like this:

ShowViewModel<MyViewModel>();

But nothing happens when you call it.

The Output Window

The output window is definitely your friend with MVVMCross; it may say something like this:

mvx:Diagnostic: 36.44 Error seen during navigation request to MyViewModel – error KeyNotFoundException: Could not find view for MyApp.PCL.ViewModels.MyViewModel
at Cirrious.MvvmCross.Views.MvxViewsContainer.GetViewType(Type viewModelType)
at Cirrious.MvvmCross.WindowsStore.Views.MvxStoreViewPresenter.Show(MvxViewModelRequest request)

So, what’s the problem?

Some things to check: firstly, check that you are using an MVVMCross view; that is, for example, in Windows 8, you need your page to inherit from MvxStorePage, not Page:

Conclusion

Nothing here that you won’t see on one of Stuart Lodge’s tutorials, and probably a good handful of SO questions. So now it’s here as well.

Updating a Progress Bar using MVVM Cross

As usual with these posts, although the specific code in the article relates to MVVM Cross, it should be applicable to any MVVM framework. Where it is specific, I’ll try to flag that up.

The Scenario

In the current game that I’m writing in MVVM Cross (yes, that’s right – a game), I have a situation where the user selects to create a “New Game” and the game world needs to be generated. As this can take some time, I want to display a progress bar. Roughly speaking, the process flow is as follows:

On the Menu Page, the User selects “New Game”.
The Menu View Model calls a service that creates the game world.
It then calls the Main Page View Model to display the main page.

The Problem

Basically, communicating between view models without tightly coupling them together.

That’s what messages are for isn’t it?

Yes.

Here’s my implementation.

First step is to add the progress bar to the screen that you want to update:

<views:MvxStorePage
    x:Class=…
    xmlns:converters="using:MyGame.Converters"
    mc:Ignorable="d">

    <views:MvxStorePage.Resources>
        <converters:BooleanToVisibilityConverter x:Key="BooleanToVisibilityConv"/>    
    </views:MvxStorePage.Resources>

    …

    <ProgressBar Value="{Binding LoadingProgress}" Maximum="{Binding TotalProgress}" Margin="20" Visibility="{Binding IsLoading, Converter={StaticResource BooleanToVisibilityConv}}"/>

There are three properties bound here: None exist yet. Obviously, if you want the progress bar to always display, you might not need all three.

Let’s create the properties in the VM:

        private bool _isLoading = false;
        public bool IsLoading
        {
            get { return _isLoading; }
            set
            {
                _isLoading = value;
                RaisePropertyChanged(() => IsLoading);
            }
        }

        private int _loadingProgress = 0;
        public int LoadingProgress
        {
            get { return _loadingProgress; }
            set
            {
                _loadingProgress = value;
                RaisePropertyChanged(() => LoadingProgress);
            }
        }

        private int _totalProgress = 0;
        public int TotalProgress
        {
            get { return _totalProgress; }
            set
            {
                _totalProgress = value;
                RaisePropertyChanged(() => TotalProgress);
            }
        }

You will also need to declare the BooleanToVisiblityConverter:

    public class BooleanToVisibilityConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, string language)
        {
            return (bool)value ? Visibility.Visible : Visibility.Collapsed;
        }

        public object ConvertBack(object value, Type targetType, object parameter, string language)
        {
            throw new NotImplementedException();
        }
    }

Now there’s something to bind to. Next, set-up the messenger.

Messenger

You need to register the messenger object. I have a base model that I do this in, but anywhere before you use it is fine:

Mvx.LazyConstructAndRegisterSingleton<IMvxMessenger, MvxMessengerHub>();

(Warning: MVVM Cross specific)
A caveat here; if you use something like `RegisterType` to register the messenger object, that will also (appear to) work. However, it won’t actually work; it will create a fresh instance of the messenger object each time. If you decide to do it that way then you will need to inject the messenger object into the subscriber and publisher (it has to be the same instance).

Next, you need to create the message:

    class UpdateProgressMessage : MvxMessage
    {
        public UpdateProgressMessage(object sender, int currentProgress, int totalProgress) : base(sender)
        {
            CurrentProgress = currentProgress;
            TotalProgress = totalProgress;
        }

        public int CurrentProgress { get; set; }
        public int TotalProgress { get; set; }
    }

This isn’t much, but the important thing is the constructor. Okay, now let’s subscribe to that message at the start of the task:

_subscriptionTag = Messenger.Subscribe<UpdateProgressMessage>(UpdateProgress);

(A note on `_subscriptionTag` later)

`UpdateProgress` is a method defined like this:

        private void UpdateProgress(UpdateProgressMessage updateProgressMessage)
        {            
            LoadingProgress = updateProgressMessage.CurrentProgress;
            TotalProgress = updateProgressMessage.TotalProgress;
            IsLoading = (updateProgressMessage.CurrentProgress > 0 &amp;&amp; 
                updateProgressMessage.TotalProgress != updateProgressMessage.CurrentProgress);

        }

Notice that you accept the `UpdateProgressMessage`.

That note on `_subscriptionTag`

Firstly, _subscriptionTag is a class level variable, defined like this:

private MvxSubscriptionToken _subscriptionTag;

Once the task is complete you can unsubscribe. For MVVM Cross specifically, the subscription uses weak references, meaning that as soon as `_subscriptionTag` goes out of scope, it will be garbage collected, and will effectively unsubscribe (which is why it needs to be class level in the first place). Having said that, personally, I prefer things to happen in code when I tell them to, and not at some undefined and unpredictable point in the future; so, to unsubscribe:

Messenger.Unsubscribe<UpdateProgressMessage>(subscriptionTag);

Publish

Finally, just wire in the publish code. I have a helper method that instantiates the services and calls the game setup code, but this should work anywhere in the application:

Messenger.Publish<UpdateProgressMessage>(new UpdateProgressMessage(this, count, total));

Because `IMvxMessenger` is registered as a singleton, once you resolve it, you should be able to publish this from anywhere.

A Word About Threading

Okay, so this will all work, but where the task runs on the UI thread, you probably won’t see it update. Consequently, I start a new task for my long running process. Remember that if you do this, then subscribing to messages on the main thread may not work.

Conclusion

Okay, so now I have a progress bar for the set-up of my game. Like I said at the start, I think this should work for any architecture that supports IoC and messaging, but MVVM Cross seems to handle this very neatly.