chore: add support for providing a default CancellationToken factory

Author: dansiegel

src/Prism.Core/Commands/AsyncDelegateCommand.cs

@@ -17,6 +17,7 @@ public class AsyncDelegateCommand : DelegateCommandBase, IAsyncCommand
     private bool _isExecuting = false;
     private readonly Func<CancellationToken, Task> _executeMethod;
     private Func<bool> _canExecuteMethod;
+    private Func<CancellationToken> _getCancellationToken = () => CancellationToken.None;
 
     /// <summary>
     /// Creates a new instance of <see cref="AsyncDelegateCommand"/> with the <see cref="Func{Task}"/> to invoke on execution.
@@ -131,7 +132,7 @@ public bool CanExecute()
     /// <param name="parameter">Command Parameter</param>
     protected override async void Execute(object parameter)
     {
-        await Execute();
+        await Execute(_getCancellationToken());
     }
 
     /// <summary>
@@ -147,19 +148,30 @@ protected override bool CanExecute(object parameter)
     /// <summary>
     /// Enables Parallel Execution of Async Tasks
     /// </summary>
-    /// <returns></returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand"/>.</returns>
     public AsyncDelegateCommand EnableParallelExecution()
     {
         _enableParallelExecution = true;
         return this;
     }
 
+    /// <summary>
+    /// Provides a delegate callback to provide a default CancellationToken when the Command is invoked.
+    /// </summary>
+    /// <param name="factory">The default <see cref="CancellationToken"/> Factory.</param>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand"/>.</returns>
+    public AsyncDelegateCommand CancellationTokenSourceFactory(Func<CancellationToken> factory)
+    {
+        _getCancellationToken = factory;
+        return this;
+    }
+
     /// <summary>
     /// Observes a property that implements INotifyPropertyChanged, and automatically calls DelegateCommandBase.RaiseCanExecuteChanged on property changed notifications.
     /// </summary>
     /// <typeparam name="T">The object type containing the property specified in the expression.</typeparam>
     /// <param name="propertyExpression">The property expression. Example: ObservesProperty(() => PropertyName).</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand"/>.</returns>
     public AsyncDelegateCommand ObservesProperty<T>(Expression<Func<T>> propertyExpression)
     {
         ObservesPropertyInternal(propertyExpression);
@@ -170,7 +182,7 @@ public AsyncDelegateCommand ObservesProperty<T>(Expression<Func<T>> propertyExpr
     /// Observes a property that is used to determine if this command can execute, and if it implements INotifyPropertyChanged it will automatically call DelegateCommandBase.RaiseCanExecuteChanged on property changed notifications.
     /// </summary>
     /// <param name="canExecuteExpression">The property expression. Example: ObservesCanExecute(() => PropertyName).</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand"/>.</returns>
     public AsyncDelegateCommand ObservesCanExecute(Expression<Func<bool>> canExecuteExpression)
     {
         _canExecuteMethod = canExecuteExpression.Compile();
@@ -182,7 +194,7 @@ public AsyncDelegateCommand ObservesCanExecute(Expression<Func<bool>> canExecute
     /// Provides the ability to connect a delegate to catch exceptions encountered by CanExecute or the Execute methods of the DelegateCommand
     /// </summary>
     /// <param name="catch">TThe callback when a specific exception is encountered</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand"/>.</returns>
     public AsyncDelegateCommand Catch<TException>(Action<TException> @catch)
         where TException : Exception
     {
@@ -194,7 +206,7 @@ public AsyncDelegateCommand Catch<TException>(Action<TException> @catch)
     /// Provides the ability to connect a delegate to catch exceptions encountered by CanExecute or the Execute methods of the DelegateCommand
     /// </summary>
     /// <param name="catch">The generic / default callback when an exception is encountered</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand"/>.</returns>
     public AsyncDelegateCommand Catch(Action<Exception> @catch)
     {
         ExceptionHandler.Register<Exception>(@catch);
@@ -203,7 +215,7 @@ public AsyncDelegateCommand Catch(Action<Exception> @catch)
 
     Task IAsyncCommand.ExecuteAsync(object? parameter)
     {
-        return Execute(default);
+        return Execute(_getCancellationToken());
     }
 
     Task IAsyncCommand.ExecuteAsync(object? parameter, CancellationToken cancellationToken)

src/Prism.Core/Commands/AsyncDelegateCommand{T}.cs

@@ -18,6 +18,7 @@ public class AsyncDelegateCommand<T> : DelegateCommandBase, IAsyncCommand
     private bool _isExecuting = false;
     private readonly Func<T, CancellationToken, Task> _executeMethod;
     private Func<T, bool> _canExecuteMethod;
+    private Func<CancellationToken> _getCancellationToken = () => CancellationToken.None;
 
     /// <summary>
     /// Creates a new instance of <see cref="AsyncDelegateCommand{T}"/> with the <see cref="Func{Task}"/> to invoke on execution.
@@ -135,7 +136,7 @@ protected override async void Execute(object parameter)
     {
         try
         {
-            await Execute((T)parameter);
+            await Execute((T)parameter, _getCancellationToken());
         }
         catch (Exception ex)
         {
@@ -171,19 +172,30 @@ protected override bool CanExecute(object parameter)
     /// <summary>
     /// Enables Parallel Execution of Async Tasks
     /// </summary>
-    /// <returns></returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand{T}"/>.</returns>
     public AsyncDelegateCommand<T> EnableParallelExecution()
     {
         _enableParallelExecution = true;
         return this;
     }
 
+    /// <summary>
+    /// Provides a delegate callback to provide a default CancellationToken when the Command is invoked.
+    /// </summary>
+    /// <param name="factory">The default <see cref="CancellationToken"/> Factory.</param>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand{T}"/>.</returns>
+    public AsyncDelegateCommand<T> CancellationTokenSourceFactory(Func<CancellationToken> factory)
+    {
+        _getCancellationToken = factory;
+        return this;
+    }
+
     /// <summary>
     /// Observes a property that implements INotifyPropertyChanged, and automatically calls DelegateCommandBase.RaiseCanExecuteChanged on property changed notifications.
     /// </summary>
     /// <typeparam name="TType">The type of the return value of the method that this delegate encapsulates</typeparam>
     /// <param name="propertyExpression">The property expression. Example: ObservesProperty(() => PropertyName).</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand{T}"/>.</returns>
     public AsyncDelegateCommand<T> ObservesProperty<TType>(Expression<Func<TType>> propertyExpression)
     {
         ObservesPropertyInternal(propertyExpression);
@@ -194,7 +206,7 @@ public AsyncDelegateCommand<T> ObservesProperty<TType>(Expression<Func<TType>> p
     /// Observes a property that is used to determine if this command can execute, and if it implements INotifyPropertyChanged it will automatically call DelegateCommandBase.RaiseCanExecuteChanged on property changed notifications.
     /// </summary>
     /// <param name="canExecuteExpression">The property expression. Example: ObservesCanExecute(() => PropertyName).</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand{T}"/>.</returns>
     public AsyncDelegateCommand<T> ObservesCanExecute(Expression<Func<bool>> canExecuteExpression)
     {
         Expression<Func<T, bool>> expression = Expression.Lambda<Func<T, bool>>(canExecuteExpression.Body, Expression.Parameter(typeof(T), "o"));
@@ -207,7 +219,7 @@ public AsyncDelegateCommand<T> ObservesCanExecute(Expression<Func<bool>> canExec
     /// Provides the ability to connect a delegate to catch exceptions encountered by CanExecute or the Execute methods of the DelegateCommand
     /// </summary>
     /// <param name="catch">TThe callback when a specific exception is encountered</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand{T}"/>.</returns>
     public AsyncDelegateCommand<T> Catch<TException>(Action<TException> @catch)
         where TException : Exception
     {
@@ -219,7 +231,7 @@ public AsyncDelegateCommand<T> Catch<TException>(Action<TException> @catch)
     /// Provides the ability to connect a delegate to catch exceptions encountered by CanExecute or the Execute methods of the DelegateCommand
     /// </summary>
     /// <param name="catch">The generic / default callback when an exception is encountered</param>
-    /// <returns>The current instance of DelegateCommand</returns>
+    /// <returns>The current instance of <see cref="AsyncDelegateCommand{T}"/>.</returns>
     public AsyncDelegateCommand<T> Catch(Action<Exception> @catch)
     {
         ExceptionHandler.Register<Exception>(@catch);
@@ -231,7 +243,7 @@ async Task IAsyncCommand.ExecuteAsync(object? parameter)
         try
         {
             // If T is not nullable this may throw an exception
-            await Execute((T)parameter, default);
+            await Execute((T)parameter, _getCancellationToken());
         }
         catch (Exception ex)
         {

tests/Prism.Core.Tests/Commands/AsyncDelegateCommandFixture.cs

@@ -1,5 +1,6 @@
-using System.Threading.Tasks;
-using System.Threading;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Windows.Input;
 using Prism.Commands;
 using Xunit;
 
@@ -116,4 +117,19 @@ async Task Execute(CancellationToken token)
         Assert.True(executionStarted);
         Assert.False(executed);
     }
+
+    [Fact]
+    public async Task ICommandExecute_UsesDefaultTokenSourceFactory()
+    {
+        var cts = new CancellationTokenSource();
+        var command = new AsyncDelegateCommand((token) => Task.Delay(1000, token))
+            .CancellationTokenSourceFactory(() => cts.Token);
+        ICommand iCommand = command;
+        iCommand.Execute(null);
+
+        Assert.True(command.IsExecuting);
+        cts.Cancel();
+
+        Assert.False(command.IsExecuting);
+    }
 }