UI线程上的任务继续

Question

是否有一种"标准"方式来指定任务延续应该在创建初始任务的线程上运行？

目前我有下面的代码 - 它正在工作,但跟踪调度程序和创建第二个动作似乎是不必要的开销.

dispatcher = Dispatcher.CurrentDispatcher;
Task task = Task.Factory.StartNew(() =>
{
    DoLongRunningWork();
});

Task UITask= task.ContinueWith(() =>
{
    dispatcher.Invoke(new Action(() =>
    {
        this.TextBlock1.Text = "Complete"; 
    }
});

Answer 1

用以下方式调用延续TaskScheduler.FromCurrentSynchronizationContext():

    Task UITask= task.ContinueWith(() =>
    {
     this.TextBlock1.Text = "Complete"; 
    }, TaskScheduler.FromCurrentSynchronizationContext());

仅当当前执行上下文位于UI线程上时,这才适用.

Answer 2

使用异步你只需:

await Task.Run(() => do some stuff);
// continue doing stuff on the same context as before.
// while it is the default it is nice to be explicit about it with:
await Task.Run(() => do some stuff).ConfigureAwait(true);

然而:

await Task.Run(() => do some stuff).ConfigureAwait(false);
// continue doing stuff on the same thread as the task finished on.

Answer 3

如果您有需要发送到UI的返回值,则可以使用如下通用版本:

在我的例子中,这是从MVVM ViewModel调用的.

var updateManifest = Task<ShippingManifest>.Run(() =>
    {
        Thread.Sleep(5000);  // prove it's really working!

        // GenerateManifest calls service and returns 'ShippingManifest' object 
        return GenerateManifest();  
    })

    .ContinueWith(manifest =>
    {
        // MVVM property
        this.ShippingManifest = manifest.Result;

        // or if you are not using MVVM...
        // txtShippingManifest.Text = manifest.Result.ToString();    

        System.Diagnostics.Debug.WriteLine("UI manifest updated - " + DateTime.Now);

    }, TaskScheduler.FromCurrentSynchronizationContext());

Answer 4

我只是想添加这个版本,因为这是一个非常有用的线程,我认为这是一个非常简单的实现.如果多线程应用程序我在各种类型中多次使用它:

 Task.Factory.StartNew(() =>
      {
        DoLongRunningWork();
        Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action(() =>
              { txt.Text = "Complete"; }));
      });

Answer 5

通过谷歌来到这里，因为我正在寻找一种在 Task.Run 调用后在 ui 线程上执行操作的好方法 - 使用以下代码，您可以使用它await再次返回到 UI 线程。

我希望这可以帮助别人。

public static class UI
{
    public static DispatcherAwaiter Thread => new DispatcherAwaiter();
}

public struct DispatcherAwaiter : INotifyCompletion
{
    public bool IsCompleted => Application.Current.Dispatcher.CheckAccess();

    public void OnCompleted(Action continuation) => Application.Current.Dispatcher.Invoke(continuation);

    public void GetResult() { }

    public DispatcherAwaiter GetAwaiter()
    {
        return this;
    }
}

用法：

public static class UI
{
    public static DispatcherAwaiter Thread => new DispatcherAwaiter();
}

public struct DispatcherAwaiter : INotifyCompletion
{
    public bool IsCompleted => Application.Current.Dispatcher.CheckAccess();

    public void OnCompleted(Action continuation) => Application.Current.Dispatcher.Invoke(continuation);

    public void GetResult() { }

    public DispatcherAwaiter GetAwaiter()
    {
        return this;
    }
}