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问题描述
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.
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
// ...
}
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
// ...
}
What are the underwater rocks for async event handlers, besides possible re-entrancy?
解决方案
The guideline is to avoid async void except when used in an event handler, so using async void in an event handler is OK.
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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