Add CancellationToken Parameter to Methods Returning Task and ValueTask

.editorconfig

@@ -71,7 +71,7 @@ csharp_style_pattern_matching_over_is_with_cast_check = true:suggestion
 csharp_style_pattern_matching_over_as_with_null_check = true:suggestion
 csharp_style_inlined_variable_declaration = true:suggestion
 csharp_style_throw_expression = true:suggestion
-csharp_style_conditional_delegate_call = true:suggestions
+csharp_style_conditional_delegate_call = true:suggestion
 
 # Naming rules
 
@@ -122,6 +122,9 @@ dotnet_diagnostic.CA1050.severity = error
 # CA2016: Forward the 'cancellationToken' parameter methods that take one
 dotnet_diagnostic.CA2016.severity = error
 
+# CA1068: CancellationToken parameters must come last
+dotnet_diagnostic.CA1068.severity = error
+
 # CA2208: Method passes parameter as the paramName argument to a ArgumentNullException constructor. Replace this argument with one of the method's parameter names. Note that the provided parameter name should have the exact casing as declared on the method.
 dotnet_diagnostic.CA2208.severity = error
 

CONTRIBUTING.md

@@ -125,6 +125,12 @@ Here we will have some:
 ### Debug Logging
 * Always use `Trace.WriteLine()` instead of `Debug.WriteLine` for debug logging because `Debug.WriteLine` is removed by the compiler in Release builds
 
+### Methods Returning Task and ValueTask
+* Always include a `CancellationToken` as a parameter to every method returning `Task` or `ValueTask`
+* If the method is public, provide a the default value for the `CancellationToken` (eg `CancellationToken token = default`)
+  * If the method is not publc, do not provide a default value for the `CancellationToken`
+* Use `CancellationToken.ThrowIfCancellationRequested()` to verify the `CancellationToken`
+
 ### Enums
 * Always use `Unknown` at index 0 for return types that may have a value that is not known
 * Always use `Default` at index 0 for option types that can use the system default option

samples/CommunityToolkit.Maui.Sample/Pages/Alerts/SnackbarPage.xaml.cs

@@ -60,15 +60,18 @@ async void DisplayCustomSnackbarButtonClicked(object? sender, EventArgs args)
 				options,
 				DisplayCustomSnackbarButton);
 
-			await customSnackbar.Show();
+			var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+			await customSnackbar.Show(cts.Token);
 
 			DisplayCustomSnackbarButton.Text = dismissCustomSnackbarText;
 		}
 		else if (DisplayCustomSnackbarButton.Text is dismissCustomSnackbarText)
 		{
 			if (customSnackbar is not null)
 			{
-				await customSnackbar.Dismiss();
+				var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+				await customSnackbar.Dismiss(cts.Token);
+
 				customSnackbar.Dispose();
 			}
 
@@ -102,7 +105,7 @@ await Application.Current.MainPage.Navigation.PushModalAsync(new ContentPage
 
 					Children =
 					{
-						new Button { Command = new AsyncRelayCommand(() => Snackbar.Make("Snackbar in a Modal Page").Show()) }
+						new Button { Command = new AsyncRelayCommand(token => Snackbar.Make("Snackbar in a Modal Page").Show(token)) }
 							.Top().CenterHorizontal()
 							.Text("Display Snackbar"),
 

samples/CommunityToolkit.Maui.Sample/Pages/Alerts/ToastPage.xaml.cs

@@ -16,13 +16,17 @@ public ToastPage(ToastViewModel toastViewModel) : base(toastViewModel)
 	async void ShowToastButtonClicked(object? sender, EventArgs args)
 	{
 		var toast = Toast.Make("This is a default Toast.");
-		await toast.Show();
+
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await toast.Show(cts.Token);
 	}
 
 	async void ShowCustomToastButtonClicked(object? sender, EventArgs args)
 	{
 		var toast = Toast.Make("This is a big Toast.", ToastDuration.Long, 30d);
-		await toast.Show();
+
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await toast.Show(cts.Token);
 	}
 
 	async void DisplayToastInModalButtonClicked(object? sender, EventArgs e)
@@ -37,7 +41,7 @@ await Application.Current.MainPage.Navigation.PushModalAsync(new ContentPage
 
 					Children =
 					{
-						new Button { Command = new AsyncRelayCommand(() => Toast.Make("Toast in a Modal Page").Show()) }
+						new Button { Command = new AsyncRelayCommand(token => Toast.Make("Toast in a Modal Page").Show(token)) }
 							.Top().CenterHorizontal()
 							.Text("Display Toast"),
 

samples/CommunityToolkit.Maui.Sample/Pages/Behaviors/AnimationBehaviorPage.xaml

@@ -16,7 +16,7 @@
             <Label.FormattedText>
                 <FormattedString>
                     <FormattedString.Spans>
-                        <Span Text="AnimationBehavor is a Behavior that can be attached to any VisualElement, allowing developers to: trigger animations via: ICommand AnimateCommand." />
+                        <Span Text="AnimationBehavior is a Behavior that can be attached to any VisualElement, allowing developers to: trigger animations via: ICommand AnimateCommand." />
                         <Span Text="{x:Static system:Environment.NewLine}" />
                         <Span Text="* use the default of a TapGestureRecognizer being added to the attached VisualElement" />
                         <Span Text="{x:Static system:Environment.NewLine}" />

samples/CommunityToolkit.Maui.Sample/Pages/Behaviors/AnimationBehaviorPage.xaml.cs

@@ -13,16 +13,17 @@ public AnimationBehaviorPage(AnimationBehaviorViewModel animationBehaviorViewMod
 
 class SampleScaleAnimation : BaseAnimation
 {
-	public override async Task Animate(VisualElement view)
+	public override async Task Animate(VisualElement view, CancellationToken token)
 	{
-		await view.ScaleTo(1.2, Length, Easing);
-		await view.ScaleTo(1, Length, Easing);
+		await view.ScaleTo(1.2, Length, Easing).WaitAsync(token);
+		await view.ScaleTo(1, Length, Easing).WaitAsync(token);
 	}
 }
 
 class SampleScaleToAnimation : BaseAnimation
 {
 	public double Scale { get; set; }
 
-	public override Task Animate(VisualElement view) => view.ScaleTo(Scale, Length, Easing);
+	public override Task Animate(VisualElement view, CancellationToken token)
+		=> view.ScaleTo(Scale, Length, Easing).WaitAsync(token);
 }

samples/CommunityToolkit.Maui.Sample/Pages/Behaviors/NumericValidationBehaviorPage.xaml.cs

@@ -16,11 +16,11 @@ async void SetEntryValue(object? sender, EventArgs e)
 	{
 		var toastVisibilityTimeSpan = TimeSpan.FromSeconds(5);
 		var cts = new CancellationTokenSource(toastVisibilityTimeSpan);
-		
+
 		await Toast.Make($"The app will crash because `null` is an invalid value for {nameof(NumericValidationBehavior)}.\nOptionally, {nameof(Options)}.{nameof(Options.SetShouldSuppressExceptionsInBehaviors)} can be set to true", Core.ToastDuration.Long).Show(cts.Token);
 
 		await Task.Delay(toastVisibilityTimeSpan, cts.Token);
-		
+
 		SafeEntry.Text = null;
 	}
 }

samples/CommunityToolkit.Maui.Sample/Pages/Views/AvatarView/AvatarViewGesturesPage.xaml.cs

@@ -7,19 +7,39 @@ public partial class AvatarViewGesturesPage : BasePage<AvatarViewGesturesViewMod
 {
 	public AvatarViewGesturesPage(AvatarViewGesturesViewModel avatarViewGesturesViewModel) : base(avatarViewGesturesViewModel) => InitializeComponent();
 
-	async void DragGestureRecognizer_DragStarting(object sender, DragStartingEventArgs e) => await ShowToastGestureMessage("AvatarView drag gesture recognizer, drag starting.");
+	async void DragGestureRecognizer_DragStarting(object sender, DragStartingEventArgs e)
+	{
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await ShowToastGestureMessage("AvatarView drag gesture recognizer, drag starting.", cts.Token);
+	}
 
-	async void PanGestureRecognizer_PanUpdated(object sender, PanUpdatedEventArgs e) => await ShowToastGestureMessage("AvatarView pan gesture recognizer, pan updated.");
+	async void PanGestureRecognizer_PanUpdated(object sender, PanUpdatedEventArgs e)
+	{
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await ShowToastGestureMessage("AvatarView pan gesture recognizer, pan updated.", cts.Token);
+	}
 
-	async void PinchGestureRecognizer_PinchUpdated(object sender, PinchGestureUpdatedEventArgs e) => await ShowToastGestureMessage("AvatarView pinch gesture recognizer, pinch updated.");
+	async void PinchGestureRecognizer_PinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
+	{
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await ShowToastGestureMessage("AvatarView pinch gesture recognizer, pinch updated.", cts.Token);
+	}
 
-	async void SwipeGestureRecognizer_Swiped(object sender, SwipedEventArgs e) => await ShowToastGestureMessage("AvatarView swipe gesture recognizer, swiped.");
+	async void SwipeGestureRecognizer_Swiped(object sender, SwipedEventArgs e)
+	{
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await ShowToastGestureMessage("AvatarView swipe gesture recognizer, swiped.", cts.Token);
+	}
 
-	async void TapGestureRecognizer_Tapped(object sender, EventArgs e) => await ShowToastGestureMessage("AvatarView Tap Gesture Recognizer, tapped.");
+	async void TapGestureRecognizer_Tapped(object sender, EventArgs e)
+	{
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await ShowToastGestureMessage("AvatarView Tap Gesture Recognizer, tapped.", cts.Token);
+	}
 
-	static async Task ShowToastGestureMessage(string message)
+	static Task ShowToastGestureMessage(string message, CancellationToken token)
 	{
 		Core.IToast toast = Toast.Make(message, Core.ToastDuration.Short);
-		await toast.Show();
+		return toast.Show(token);
 	}
 }

samples/CommunityToolkit.Maui.Sample/Pages/Views/DrawingViewPage.xaml.cs

@@ -30,23 +30,29 @@ void LoadPointsButtonClicked(object sender, EventArgs e)
 
 	async void GetCurrentDrawingViewImageClicked(object sender, EventArgs e)
 	{
-		var stream = await DrawingViewControl.GetImageStream(GestureImage.Width, GestureImage.Height);
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		var stream = await DrawingViewControl.GetImageStream(GestureImage.Width, GestureImage.Height, cts.Token);
+
 		GestureImage.Source = ImageSource.FromStream(() => stream);
 	}
 
 	async void GenerateImageButtonClicked(object sender, EventArgs e)
 	{
 		var lines = GenerateLines(2);
-		await DrawImage(lines);
+
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await DrawImage(lines, cts.Token);
 	}
 
-	async Task DrawImage(IEnumerable<DrawingLine> lines)
+	async Task DrawImage(IEnumerable<DrawingLine> lines, CancellationToken token)
 	{
 		var drawingLines = lines.ToList();
 		var points = drawingLines.SelectMany(x => x.Points).ToList();
 		var stream = await DrawingView.GetImageStream(drawingLines,
 			new Size(points.Max(x => x.X) - points.Min(x => x.X), points.Max(x => x.Y) - points.Min(x => x.Y)),
-			Colors.Gray);
+			Colors.Gray,
+			token);
+
 		GestureImage.Source = ImageSource.FromStream(() => stream);
 	}
 
@@ -71,7 +77,10 @@ async void OnDrawingLineCompleted(object sender, DrawingLineCompletedEventArgs e
 	{
 		var width = GetSide(GestureImage.Width);
 		var height = GetSide(GestureImage.Height);
-		var stream = await e.LastDrawingLine.GetImageStream(width, height, Colors.Gray.AsPaint());
+
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		var stream = await e.LastDrawingLine.GetImageStream(width, height, Colors.Gray.AsPaint(), cts.Token);
+
 		GestureImage.Source = ImageSource.FromStream(() => stream);
 	}
 }

samples/CommunityToolkit.Maui.Sample/Pages/Views/LazyView/CustomLazyView.cs

@@ -4,13 +4,13 @@ namespace CommunityToolkit.Maui.Sample.Pages.Views.LazyView;
 
 public class CustomLazyView<TView> : Maui.Views.LazyView where TView : View, new()
 {
-	public override async ValueTask LoadViewAsync()
+	public override async ValueTask LoadViewAsync(CancellationToken token)
 	{
 		// display a loading indicator
 		Content = new ActivityIndicator { IsRunning = true }.Center();
 
 		// simulate a long running task
-		await Task.Delay(3000);
+		await Task.Delay(3000, token);
 
 		// load the view
 		Content = new TView { BindingContext = BindingContext };

samples/CommunityToolkit.Maui.Sample/Pages/Views/LazyView/LazyViewPage.xaml

@@ -54,7 +54,7 @@
             <Label Text="Lazy Loading Based On User Action" Style="{StaticResource Heading}"/>
             <Label Text="{Binding Source={x:Reference LazyUserAction}, Path=HasLazyViewLoaded, StringFormat='HasLazyViewLoaded = {0}'}" Style="{StaticResource Heading}"/>
             <Button Text="Load View Now" Clicked="LoadLazyView_Clicked" WidthRequest="200" IsVisible="{Binding Source={x:Reference LazyUserAction}, Path=HasLazyViewLoaded, Converter={mct:InvertedBoolConverter}}" />
-            <local:MyLazyView x:Name="LazyUserAction" Style="{StaticResource MyViewStyle}"/>
+            <local:MyViewLazyView x:Name="LazyUserAction" Style="{StaticResource MyViewStyle}"/>
         </VerticalStackLayout>
     </ScrollView>
 </pages:BasePage>

samples/CommunityToolkit.Maui.Sample/Pages/Views/LazyView/LazyViewPage.xaml.cs

@@ -12,11 +12,14 @@ public LazyViewPage(LazyViewViewModel viewModel) : base(viewModel)
 	protected override async void OnAppearing()
 	{
 		base.OnAppearing();
-		await LazyActiviation.LoadViewAsync();
+
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await LazyActiviation.LoadViewAsync(cts.Token);
 	}
 
 	async void LoadLazyView_Clicked(object sender, EventArgs e)
 	{
-		await LazyUserAction.LoadViewAsync();
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		await LazyUserAction.LoadViewAsync(cts.Token);
 	}
 }

samples/CommunityToolkit.Maui.Sample/Pages/Views/LazyView/MyViewLazyView.cs

@@ -0,0 +1,11 @@
+using CommunityToolkit.Maui.Views;
+
+namespace CommunityToolkit.Maui.Sample.Pages.Views.LazyView;
+
+class MyViewLazyView : LazyView<MyView>
+{
+	public override async ValueTask LoadViewAsync(CancellationToken token)
+	{
+		await base.LoadViewAsync(token);
+	}
+}