Using async await still freezes GUI

Question

I would like to handle long running operation in separate thread and return control back to GUI thread ASAP using async/await pattern as follows:

private         


        

Answer 1

You're using Thread.Sleep which blocks the thread. Use Task.Delay instead, which uses a timer internally and asynchronously yields control back to the caller:

private async void Button_Click(object sender, RoutedEventArgs e)
{
    await TestAsync();
    txtResult.Text = "Done!";
}

private async Task TestAsync()
{
    await Task.Delay(3000);
    return 0;
}

Edit

As you posted new code, I suggest you isolate the callback that needs to run after the log running process, and save yourself the Dispatcher.Invoke and replace it with the use of async-await which will land you on the right synchronization context for you:

private async void Button_Click(object sender, RoutedEventArgs e)
{
    await Task.Run(Test);
    CallBack();
}

private void Callback()
{
    txtResult.Text = "Done!"
}

private void Test()
{
    Thread.Sleep(3000); //long running operation, not necessarily pause
}