Thread: Need help with asynchronous data fetching in C#

Hi John,

Your implementation looks mostly correct! The Progress<T> class is designed to handle the marshaling to the UI thread automatically when you report progress. The issue you're seeing with the UI freezing or not updating promptly might be related to how Task.Run is used in conjunction with the `async void` event handler.

While Progress<T> does the marshalling for the callback, the `async void` itself can be problematic in event handlers. It's generally recommended to use `async Task` for event handlers if possible, or ensure you're correctly awaiting the task.

Consider this alternative:

public async Task FetchDataButton_ClickAsync(object sender, RoutedEventArgs e) // Changed to async Task
{
    var progress = new Progress(data =>
    {
        OutputTextBox.AppendText(data + Environment.NewLine);
    });

    await Task.Run(() => DoLongOperation(progress));
}

// Keep DoLongOperation as is
            

Also, ensure your `OutputTextBox` is correctly configured for updates (e.g., not blocked by other operations).

Sarah's advice is solid. Just to add, sometimes the issue is simply that the UI thread is still very busy processing other events, even though the `Progress` callback is correctly scheduled. If you have a very high frequency of progress updates, it might appear sluggish.

Another approach is to use `Application.Current.Dispatcher.Invoke` directly within the loop if you want more explicit control, though Progress<T> is usually cleaner:

private void DoLongOperationWithDispatcher(IProgress<string> progress)
{
    for (int i = 0; i < 10; i++)
    {
        Thread.Sleep(500); // Simulate work
        string message = $"Processing item {i + 1}...";

        // Explicitly invoke on UI thread if needed, though Progress should handle this
        // Application.Current.Dispatcher.Invoke(() =>
        // {
        //     OutputTextBox.AppendText(message + Environment.NewLine);
        // });

        progress.Report(message); // Progress handles the dispatching
    }
    progress.Report("Operation completed!");
}
                    

The primary takeaway is that Progress<T> leverages the synchronization context of the calling thread when the Report method is invoked. For UI applications, this context is usually the UI thread.

Thanks Sarah and Alex!

I tried changing the event handler to async Task and it seems to have resolved the sluggishness and freezing. It's much smoother now. I also appreciate the explanation about the synchronization context with Progress<T>. That clarifies things a lot.

I'll stick with the Progress<T> approach as it's cleaner. Thanks again for the help!