有没有办法让我运行的方法立即停止使用cts.Cancel();? [英] Is there a way I can cause a running method to stop immediately with a cts.Cancel();

问题描述

我有创建CancellationTokenSource并将其传递给方法的代码.

I have code that creates a CancellationTokenSource and that passes it to a method.

我在另一个发布cts.Cancel()的应用程序中都有代码.

I have code in another are of the app that issues a cts.Cancel();

有没有一种方法可以使该方法立即停止，而不必等待while循环中的两行完成?

Is there a way that I can cause that method to stop immediately without me having to wait for the two lines inside the while loop to finish?

请注意，如果它引起了我可以处理的异常，那我就可以了.

Note that I would be okay if it caused an exception that I could handle.

public async Task OnAppearing()
{
   cts = new CancellationTokenSource();
   await GetCards(cts.Token);
}

public async Task GetCards(CancellationToken ct)
{
   while (!ct.IsCancellationRequested)
   {
      App.viewablePhrases = App.DB.GetViewablePhrases(Settings.Mode, Settings.Pts);
      await CheckAvailability();
   }
}

推荐答案

我的建议:

1. 修改GetViewablePhrases和CheckAvailability，以便您可以将CancellationToken传递给它们；
2. 使用 ct.ThrowIfCancellationRequested()在这些函数中；
3. 尝试/捕获GetCards中的OperationCanceledException；

关于您的功能，我不知道它们在内部的工作原理.但让我们假设您在其中一个内部有一个长期运行的迭代:

As for your your functions I don't know how exactly they work inside. But let's assume you have a long running iteration inside one of them:

CheckAvailability(CancellationToken ct)
{
    for(;;) 
    {
        // if cts.Cancel() was executed - this method throws the OperationCanceledException
        // if it wasn't the method does nothing
        ct.ThrowIfCancellationRequested(); 
        ...calculations... 
    } 
}

或者说您要在其中一个函数中访问数据库，并且您知道此过程将花费一些时间:

Or let's say you are going to access your database inside one of the function and you know that this process is going to take a while:

CheckAvailability(CancellationToken ct)
{
    ct.ThrowIfCancellationRequested();
    AccessingDatabase();
}

这不仅会阻止您的函数继续执行，还会将执行者的任务状态设置为TaskStatus.Canceled

This will not only prevent your functions from proceeding with execution, this also will set the executioner Task status as TaskStatus.Canceled

别忘了捕获异常:

public async Task GetCards(CancellationToken ct)
{
   try
   {
      App.viewablePhrases = App.DB.GetViewablePhrases(Settings.Mode, Settings.Pts, ct);
      await CheckAvailability(ct);
   }
   catch(OperationCanceledException ex)
   {
       // handle the cancelation...
   }
   catch
   {
       // handle the unexpected exception
   }
}

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