Question

Since the Windows 8 consumer preview was released a few days ago, I am working on the new WinRT (for Metro Applications) in C# and I had ported my self written IRC class to the new threading and networking.

The problem is: My class is running an thread for receiving messages from the server. If this happens, the thread is making some parsing and then firing an event to inform the application about this. The subscribed function then ‘should’ update the UI (an textblock).

This is the problem, the thread cannot update the UI and the invoker method that has worked with .NET 4.0 doesn’t seem to be possible anymore. Is there an new workaround for this or even an better way to update the UI ? If I try to update the UI from the event subscriber i will get this Exception:

The application called an interface that was marshalled for a
different thread (Exception from HRESULT: 0x8001010E
(RPC_E_WRONG_THREAD))

Answer 1

The preferred way to deal with this in WinRT (and C# 5 in general) is to use async–await:

private async void Button_Click(object sender, RoutedEventArgs e)
{
    string text = await Task.Run(() => Compute());
    this.TextBlock.Text = text;
}

Here, the Compute() method will run on a background thread and when it finishes, the rest of the method will execute on the UI thread. In the meantime, the UI thread is free to do whatever it needs (like processing other events).

But if you don’t want to or can’t use async, you can use Dispatcher, in a similar (although different) way as in WPF:

private void Button_Click(object sender, RoutedEventArgs e)
{
    Task.Run(() => Compute());
}

private void Compute()
{
    // perform computation here

    Dispatcher.Invoke(CoreDispatcherPriority.Normal, ShowText, this, resultString);
}

private void ShowText(object sender, InvokedHandlerArgs e)
{
    this.TextBlock.Text = (string)e.Context;
}