async method cannot return void - How can I handle this?

Question

I have a phone application. When a screen displays I start a timer like this:

 base.OnAppearing();
 {
     timerRunning = true;
     Device.BeginInvokeOnMainThread(() => showGridTime(5));
 }
 async void showGridTime(int time)
 { 
     while (timerRunning)
     {
         var tokenSource = new CancellationTokenSource();
         await Task.Delay(time, tokenSource.Token);
         detailGrid.IsVisible = true;
     }
 }

The code seems to work but there is a warning message in the IDE saying that an async method cannot return null.

Given this code can someone help and give me advice on what I should return and if I am going about this in the correct way?

Possible duplicate of async/await - when to return a Task vs void? — Peter B
– Peter B, Commented Nov 29, 2016 at 8:26

Zein Makki · Accepted Answer · 2016-11-30 07:17:28Z

4

Just return a task:

async Task ShowGridTimeAsync(int time)
 { 
     while (timerRunning)
     {
         var tokenSource = new CancellationTokenSource();
         await Task.Delay(time, tokenSource.Token);
         detailGrid.IsVisible = true;
     }
 }

This is necessary to have the caller of this method know when it is completed and act accordingly.

It is not recommended to create async void methods unless you're creating an event or forced to do that in order to meet an interface signature.

edited Nov 30, 2016 at 7:17

answered Nov 29, 2016 at 8:26

Zein Makki

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