我应该避免“异步无效”事件处理程序？ [英] Should I avoid 'async void' event handlers?

问题描述

我知道这通常被认为是一个坏主意，用火和忘记异步无效方法来启动的任务，因为没有跟踪挂起的任务，它是棘手的处理可能这种方法中抛出的异常。

I know it is considered generally a bad idea to use fire-and-forget async void methods to start tasks, because there is no track of the pending task and it is tricky to handle exceptions which might be thrown inside such a method.

我应该尽量避免使用异步无效事件处理程序，以及？的例如，

Should I generally avoid async void event handlers, as well? For example,

private async void Form_Load(object sender, System.EventArgs e)
{
        await Task.Delay(2000); // do async work
        // ...
} 

我可以重写它是这样的：

I can rewrite it like this:

Task onFormLoadTask = null; // track the task, can implement cancellation

private void Form_Load(object sender, System.EventArgs e)
{
        this.onFormLoadTask = OnFormLoadTaskAsync(sender, e);
} 

private async Task OnFormLoadTaskAsync(object sender, System.EventArgs e)
{
        await Task.Delay(2000); // do async work
        // ...
} 

什么是水下的岩石的异步事件处理程序，除了可重入？的

推荐答案

的指导原则是避免异步无效的除了的在事件中使用时处理程序，因此，使用异步的事件处理程序无效就可以了。

The guideline is to avoid async void except when used in an event handler, so using async void in an event handler is OK.

这表示，对于的单元测试的原因，我经常喜欢分解出所有的的异步无效方法的逻辑。例如，

That said, for unit testing reasons I often like to factor out the logic of all async void methods. E.g.,

public async Task OnFormLoadAsync(object sender, EventArgs e)
{
  await Task.Delay(2000);
  ...
}

private async void Form_Load(object sender, EventArgs e)
{
  await OnFormLoadAsync(sender, e);
}

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