为什么不'；t TaskScheduler.FromCurrentSynchronizationContext在M

我感兴趣的是，为什么我们需要调用InvokeOnMainThread，而这将是TaskScheduler.FromCurrentSynchronizationContext（）的主要意图和职责？。

我正在使用Monotouch中的TPL作为iPhone应用程序来执行一些后台任务，并通过报告程序类更新UI。但似乎TaskScheduler.FromCurrentSynchronizationContext（）并没有像您所期望的那样同步到UI线程。此时，我通过使用InvokeOnMainThread使其正常工作（但仍然感觉不对），正如Xamarin网站上的线程主题所描述的那样。

我还在BugZilla上发现了一个报告的（类似的）错误，似乎已经解决了。。以及关于在MonoTouch中使用背景线程的首选方式的另一个线程问题。

下面的代码片段说明了我的问题并展示了我的行为。

    private CancellationTokenSource cancellationTokenSource;
    private void StartBackgroundTask ()
    {
        this.cancellationTokenSource = new CancellationTokenSource ();
        var cancellationToken = this.cancellationTokenSource.Token;
        var progressReporter = new ProgressReporter ();
        int n = 100;
        var uiThreadId = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine ("Start in thread " + uiThreadId);
        var task = Task.Factory.StartNew (() =>
        {
            for (int i = 0; i != n; ++i) {
                Console.WriteLine ("Work in thread " + Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep (30); 
                progressReporter.ReportProgress (() =>
                {
                    Console.WriteLine ("Reporting in thread {0} (should be {1})",
                        Thread.CurrentThread.ManagedThreadId,
                        uiThreadId);
                    this.progressBar.Progress = (float)(i + 1) / n;
                    this.progressLabel.Text = this.progressBar.Progress.ToString();
                });
            }
            return 42; // Just a mock result
        }, cancellationToken);
        progressReporter.RegisterContinuation (task, () =>
        {
            Console.WriteLine ("Result in thread {0} (should be {1})",
                Thread.CurrentThread.ManagedThreadId,
                uiThreadId);
            this.progressBar.Progress = (float)1;
            this.progressLabel.Text = string.Empty;
            Util.DisplayMessage ("Result","Background task result: " + task.Result);
        });
    }

而报表类有这些方法

    public void ReportProgress(Action action)
    {
        this.ReportProgressAsync(action).Wait();
    }
    public Task ReportProgressAsync(Action action)
    {
        return Task.Factory.StartNew(action, CancellationToken.None, TaskCreationOptions.None, TaskScheduler.FromCurrentSynchronizationContext());
    }
    public Task RegisterContinuation(Task task, Action action)
    {
        return task.ContinueWith(() => action(), CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.FromCurrentSynchronizationContext());
    }
    public Task RegisterContinuation<TResult>(Task<TResult> task, Action action)
    {
        return task.ContinueWith(() => action(), CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.FromCurrentSynchronizationContext());
    }

应用程序输出窗口中的结果为：

Start in thread 1
Work in thread 6
Reporting in thread 6 (should be 1)
Work in thread 6
Reporting in thread 6 (should be 1)
...
Result in thread 1 (should be 1)

正如您所看到的，"在线程6中工作"很好。报告也在线程6上，这是错误的。有趣的是RegisterContinuation在线程1中进行报告！！！

---

进展：我还没有弄清楚这个。。任何人

public class ProgressReporter
{
    private readonly TaskScheduler taskScheduler;
    public ProgressReporter(TaskScheduler taskScheduler)
    {
        this.taskScheduler = taskScheduler;
    }
    public Task RegisterContinuation(Task task, Action action)
    {
        return task.ContinueWith(n => action(), CancellationToken.None,
            TaskContinuationOptions.None, taskScheduler);
    }
    // Remaining members...
}

TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
ProgressReporter progressReporter = new ProgressReporter(uiScheduler);