Dispatcher.Invoke() 在 NUnit 测试中抛出 TaskCanceledException

Question

我正在尝试使用接口从我们的视图模型中抽象出 Dispatcher。我创建了该接口的模拟实现，如下所示：

public class MockIDispatcher : IDispatcher, IDisposable
{
    public MockIDispatcher()
    {
        var dispatcherThread = new Thread(Dispatcher.Run) { IsBackground = true };
        dispatcherThread.SetApartmentState(ApartmentState.STA);
        dispatcherThread.Start();

        while ((Dispatcher = Dispatcher.FromThread(dispatcherThread)) == null) Thread.Yield();  // need to wait until the thread we created has started its dispatcher
    }

    internal Dispatcher Dispatcher { get; }

    /* ... more implementation here */
}

我创建了一个虚拟 NUnit 测试，如下所示，但是对 Dispatcher.Invoke() 的调用抛出了 TaskCanceledException.

[Test]
public void TestPoc()
{
    var foo = new MockIDispatcher();
    foo.Dispatcher.Invoke(() =>
    {
        Debug.WriteLine("Hey there!");
    });
}

关于如何让这段代码正常工作有什么建议吗？我想在幕后实际使用 Dispatcher，以便更轻松地玩 SynchronizationContexts 之类的东西。

Answer 1

问题似乎与我如何在构造函数中获得 Dispatcher 有关。我如下所示更改了构造函数，这解决了问题。看起来您可能需要先在线程上实际调用 Dispatcher.CurrentDispatcher 。调用 Dispatcher.Run() 是不够的。

public MockIDispatcher()
{
    using (var mre = new ManualResetEvent(false))
    {
        Dispatcher dispatcher = null;
        var dispatcherThread = new Thread(() =>
        {
            dispatcher = Dispatcher.CurrentDispatcher;
// ReSharper disable once AccessToDisposedClosure Not Possible because we are waiting inside the using loop
            mre.Set();
            try { Dispatcher.Run(); } catch {  /* swallow exceptions */ }
        }) { IsBackground = true };

        dispatcherThread.SetApartmentState(ApartmentState.STA);
        dispatcherThread.Start();

        mre.WaitOne();
        Dispatcher = dispatcher;
    }
}

Dispatcher.Invoke() 在 NUnit 测试中抛出 TaskCanceledException

Dispatcher.Invoke() throws TaskCanceledException in NUnit Tests

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dispatcher