Updating a progress bar while awaiting async operation

February 22, 2023

I try to update a progress bar while awaiting a async IO operation. The following code is doing that.

Task<string> io = SomeOperationAsync();

while(!io.IsComplete)
{
    progressBar.Value = value // add some progress;
    await Task.Delay(TimeSpan.FromMilliseconds(200));
}    

string result = await io;

This works quite ok.The Progressbar fills up quite smoothly.

But as you see, I will check for completion every 200 ms rather than really awaiting it. I might end up waiting for up to 200 ms too long.

Is there a better way to achieve this, so that my method can immediately return once the IO operation is complete?

>Solution :

You can use .WhenAny() to return when any task completes. A small refactor to your code would return if the primary task finishes before the delay.

Task<string> io = SomeOperationAsync();

while(!io.IsComplete)
{
    progressBar.Value = value // add some progress;
    await Task.WhenAny(io, Task.Delay(TimeSpan.FromMilliseconds(200)));
}    

string result = await io;