ThreadSwitcher 新增 SynchronizationContextThreadSwitcher

CoreAppUWP/Common/ThreadSwitcher.cs

@@ -17,12 +17,12 @@ public interface IThreadSwitcher : INotifyCompletion
         /// <summary>
         /// Gets a value that indicates whether the asynchronous operation has completed.
         /// </summary>
-        bool IsCompleted => true;
+        bool IsCompleted { get; }
 
         /// <summary>
         /// Ends the await on the completed task.
         /// </summary>
-        void GetResult() { }
+        void GetResult();
 
         /// <summary>
         /// Gets an awaiter used to await this <see cref="IThreadSwitcher"/>.
@@ -31,33 +31,41 @@ void GetResult() { }
         IThreadSwitcher GetAwaiter();
     }
 
+    /// <summary>
+    /// The interface of helper type for switch thread.
+    /// </summary>
+    /// <typeparam name="T">The type of the result of <see cref="GetAwaiter"/>.</typeparam>
+    public interface IThreadSwitcher<T> : IThreadSwitcher
+    {
+        /// <summary>
+        /// Gets an awaiter used to await <see cref="T"/>.
+        /// </summary>
+        /// <returns>An awaiter instance.</returns>
+        new T GetAwaiter();
+    }
+
     /// <summary>
     /// A helper type for switch thread by <see cref="CoreDispatcher"/>. This type is not intended to be used directly from your code.
     /// </summary>
     /// <param name="Dispatcher">A <see cref="CoreDispatcher"/> whose foreground thread to switch execution to.</param>
     /// <param name="Priority">Specifies the priority for event dispatch.</param>
     [EditorBrowsable(EditorBrowsableState.Never)]
-    public readonly record struct CoreDispatcherThreadSwitcher(CoreDispatcher Dispatcher, CoreDispatcherPriority Priority = CoreDispatcherPriority.Normal) : IThreadSwitcher
+    public readonly record struct CoreDispatcherThreadSwitcher(CoreDispatcher Dispatcher, CoreDispatcherPriority Priority = CoreDispatcherPriority.Normal) : IThreadSwitcher<CoreDispatcherThreadSwitcher>
     {
-        /// <summary>
-        /// Gets a value that indicates whether the asynchronous operation has completed.
-        /// </summary>
+        /// <inheritdoc/>
         public bool IsCompleted => Dispatcher?.HasThreadAccess != false;
 
         /// <inheritdoc/>
         public void GetResult() { }
 
-        /// <summary>
-        /// Gets an awaiter used to await this <see cref="CoreDispatcherThreadSwitcher"/>.
-        /// </summary>
-        /// <returns>An awaiter instance.</returns>
+        /// <inheritdoc/>
         public CoreDispatcherThreadSwitcher GetAwaiter() => this;
 
         /// <inheritdoc/>
         IThreadSwitcher IThreadSwitcher.GetAwaiter() => this;
 
         /// <inheritdoc/>
-        public void OnCompleted(Action continuation) => _ = Dispatcher?.RunAsync(Priority, () => continuation());
+        public void OnCompleted(Action continuation) => _ = Dispatcher.RunAsync(Priority, () => continuation());
     }
 
     /// <summary>
@@ -66,48 +74,62 @@ public void GetResult() { }
     /// <param name="Dispatcher">A <see cref="DispatcherQueue"/> whose foreground thread to switch execution to.</param>
     /// <param name="Priority">Specifies the priority for event dispatch.</param>
     [EditorBrowsable(EditorBrowsableState.Never)]
-    public readonly record struct DispatcherQueueThreadSwitcher(DispatcherQueue Dispatcher, DispatcherQueuePriority Priority = DispatcherQueuePriority.Normal) : IThreadSwitcher
+    public readonly record struct DispatcherQueueThreadSwitcher(DispatcherQueue Dispatcher, DispatcherQueuePriority Priority = DispatcherQueuePriority.Normal) : IThreadSwitcher<DispatcherQueueThreadSwitcher>
     {
-        /// <summary>
-        /// Gets a value that indicates whether the asynchronous operation has completed.
-        /// </summary>
+        /// <inheritdoc/>
         public bool IsCompleted => Dispatcher?.HasThreadAccess != false;
 
         /// <inheritdoc/>
         public void GetResult() { }
 
-        /// <summary>
-        /// Gets an awaiter used to await this <see cref="DispatcherQueueThreadSwitcher"/>.
-        /// </summary>
-        /// <returns>An awaiter instance.</returns>
+        /// <inheritdoc/>
         public DispatcherQueueThreadSwitcher GetAwaiter() => this;
 
         /// <inheritdoc/>
         IThreadSwitcher IThreadSwitcher.GetAwaiter() => this;
 
         /// <inheritdoc/>
-        public void OnCompleted(Action continuation) => _ = Dispatcher?.TryEnqueue(Priority, () => continuation());
+        public void OnCompleted(Action continuation) => _ = Dispatcher.TryEnqueue(Priority, () => continuation());
+    }
+
+    /// <summary>
+    /// A helper type for switch thread by <see cref="SynchronizationContext"/>. This type is not intended to be used directly from your code.
+    /// </summary>
+    /// <param name="Context">A <see cref="SynchronizationContext"/> whose foreground thread to switch execution to.</param>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public readonly record struct SynchronizationContextThreadSwitcher(SynchronizationContext Context) : IThreadSwitcher<SynchronizationContextThreadSwitcher>
+    {
+        /// <inheritdoc/>
+        public bool IsCompleted => Context is not SynchronizationContext context
+            || SynchronizationContext.Current == context;
+
+        /// <inheritdoc/>
+        public void GetResult() { }
+
+        /// <inheritdoc/>
+        public SynchronizationContextThreadSwitcher GetAwaiter() => this;
+
+        /// <inheritdoc/>
+        IThreadSwitcher IThreadSwitcher.GetAwaiter() => this;
+
+        /// <inheritdoc/>
+        public void OnCompleted(Action continuation) => Context.Post(_ => continuation(), null);
     }
 
     /// <summary>
     /// A helper type for switch thread by <see cref="ThreadPool"/>. This type is not intended to be used directly from your code.
     /// </summary>
     /// <param name="Priority">Specifies the priority for event dispatch.</param>
     [EditorBrowsable(EditorBrowsableState.Never)]
-    public readonly record struct ThreadPoolThreadSwitcher(WorkItemPriority Priority = WorkItemPriority.Normal) : IThreadSwitcher
+    public readonly record struct ThreadPoolThreadSwitcher(WorkItemPriority Priority = WorkItemPriority.Normal) : IThreadSwitcher<ThreadPoolThreadSwitcher>
     {
-        /// <summary>
-        /// Gets a value that indicates whether the asynchronous operation has completed.
-        /// </summary>
+        /// <inheritdoc/>
         public bool IsCompleted => SynchronizationContext.Current == null;
 
         /// <inheritdoc/>
         public void GetResult() { }
 
-        /// <summary>
-        /// Gets an awaiter used to await this <see cref="ThreadPoolThreadSwitcher"/>.
-        /// </summary>
-        /// <returns>An awaiter instance.</returns>
+        /// <inheritdoc/>
         public ThreadPoolThreadSwitcher GetAwaiter() => this;
 
         /// <inheritdoc/>
@@ -138,6 +160,13 @@ public static class ThreadSwitcher
         /// <returns>An object that you can <see langword="await"/>.</returns>
         public static CoreDispatcherThreadSwitcher ResumeForegroundAsync(this CoreDispatcher dispatcher, CoreDispatcherPriority priority = CoreDispatcherPriority.Normal) => new(dispatcher, priority);
 
+        /// <summary>
+        /// A helper function—for use within a coroutine—that you can <see langword="await"/> to switch execution to a specific foreground thread. 
+        /// </summary>
+        /// <param name="context">A <see cref="SynchronizationContext"/> whose foreground thread to switch execution to.</param>
+        /// <returns>An object that you can <see langword="await"/>.</returns>
+        public static SynchronizationContextThreadSwitcher ResumeForegroundAsync(this SynchronizationContext context) => new(context);
+
         /// <summary>
         /// A helper function—for use within a coroutine—that returns control to the caller, and then immediately resumes execution on a thread pool thread.
         /// </summary>