C# 简单地停止异步方法
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simply stop an async method
提问by Jaydeep Solanki
I have this method which plays a sound, when the user taps on the screen, & I want it to stop playing it when the user taps the screen again. But the problem is "DoSomething()" method doesn't stop, it keeps going till it finishes.
我有这种播放声音的方法，当用户点击屏幕时，我希望它在用户再次点击屏幕时停止播放。但问题是“DoSomething()”方法不会停止，它会一直运行直到完成。
bool keepdoing = true;
private async void ScreenTap(object sender, System.Windows.Input.GestureEventArgs e)
{
keepdoing = !keepdoing;
if (!playing) { DoSomething(); }
}
private async void DoSomething()
{
playing = true;
for (int i = 0; keepdoing ; count++)
{
await doingsomething(text);
}
playing = false;
}
Any help will be appreciated.
Thanks :)
任何帮助将不胜感激。
谢谢 ：）
采纳答案by Stephen Cleary
This is what a CancellationTokenis for.
这就是 aCancellationToken的用途。
CancellationTokenSource cts;
private async void ScreenTap(object sender, System.Windows.Input.GestureEventArgs e)
{
if (cts == null)
{
cts = new CancellationTokenSource();
try
{
await DoSomethingAsync(cts.Token);
}
catch (OperationCanceledException)
{
}
finally
{
cts = null;
}
}
else
{
cts.Cancel();
cts = null;
}
}
private async Task DoSomethingAsync(CancellationToken token)
{
playing = true;
for (int i = 0; ; count++)
{
token.ThrowIfCancellationRequested();
await doingsomethingAsync(text, token);
}
playing = false;
}
回答by abhigdeal
Another way to use CancellationToken without throwing exceptions would be to declare/initialize CancellationTokenSource cts and pass cts.Token to DoSomething as in Stephen Cleary's answer above.
在不抛出异常的情况下使用 CancellationToken 的另一种方法是声明/初始化 CancellationTokenSource cts 并将 cts.Token 传递给 DoSomething，如上面 Stephen Cleary 的回答。
private async void DoSomething(CancellationToken token)
{
playing = true;
for (int i = 0; keepdoing ; count++)
{
if(token.IsCancellationRequested)
{
// Do whatever needs to be done when user cancels or set return value
return;
}
await doingsomething(text);
}
playing = false;
}
