Should I avoid 'async void' event handlers?

.net, async-await, asynchronous, c#, events

Solution

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);
}

Problem

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?

Original source