how can I pause the main thread, while I am updating my WPF components?

Question

I am trying to update a TextBox to display 3-2-1 and then I play a sound. This works sort of, but my sound starts to play immediately, because the Threads are not blcoking the main thread. I tried to add another Thread.Sleep(4000); in he main thread, but then it all just waits and the textbox does not display running numbers. I get number 1 in the textbox and the sound plays :(

So how do I pause the main thread, while the TextBox runs 3-2-1 and then sound?

´´´ private void Button_Click(object sender, RoutedEventArgs e) {

try
{

    ThreadPool.QueueUserWorkItem(async (o) =>

{ Dispatcher.Invoke((Action)(() => outputTextBox.Text = "3"));

await Task.Delay(1000);
Dispatcher.Invoke((Action)(() => outputTextBox.Text = "2"));
await Task.Delay(1000);
Dispatcher.Invoke((Action)(() => outputTextBox.Text = "1"));
await Task.Delay(3000);

});

Task.Delay(3000);

    if (waveOut!=null ) waveOut.Stop(); 

    Songs = db.Songs; 
    int r = rnd.Next(Songs.Count);

    System.Diagnostics.Debug.WriteLine(r);

    String name = ((Song)Songs[r]).Name1;
    System.Diagnostics.Debug.WriteLine(name);

    int start = ((Song)Songs[r]).Start1;
    System.Diagnostics.Debug.WriteLine(start);

    waveOut = new WaveOut(WaveCallbackInfo.FunctionCallback());
    

    var ms = File.OpenRead("C:\\"+name);
    var rdr = new Mp3FileReader(ms);
    var wavStream = WaveFormatConversionStream.CreatePcmStream(rdr);
    wavStream.Skip(start);
    var baStream = new BlockAlignReductionStream(wavStream);
    
    waveOut = new WaveOut(WaveCallbackInfo.FunctionCallback());
    
        waveOut.Init(baStream);

    
    
    waveOut.Play();
        
    /*
        while (waveOut.PlaybackState == PlaybackState.Playing)
        {
            Thread.Sleep(100);
        }
      */  
    
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
    return;
}

}

´´´

Answer 1

Mark your event handler with the async keyword and await the Delay calls before you play the sound:

private async void Button_Click(object sender, RoutedEventArgs e)
{
    try
    {
        outputTextBox.Text = "3";
        await Task.Delay(1000);
        outputTextBox.Text = "2";
        await Task.Delay(1000);
        outputTextBox.Text = "1";
        await Task.Delay(1000);

    // play sound:

        if (waveOut!=null)
            waveOut.Stop();

        Songs = db.Songs;
        int r = rnd.Next(Songs.Count);

        System.Diagnostics.Debug.WriteLine(r);

        String name = ((Song)Songs[r]).Name1;
        System.Diagnostics.Debug.WriteLine(name);

        int start = ((Song)Songs[r]).Start1;
        System.Diagnostics.Debug.WriteLine(start);

        waveOut = new WaveOut(WaveCallbackInfo.FunctionCallback());


        var ms = File.OpenRead("C:\\"+name);
        var rdr = new Mp3FileReader(ms);
        var wavStream = WaveFormatConversionStream.CreatePcmStream(rdr);
        wavStream.Skip(start);
        var baStream = new BlockAlignReductionStream(wavStream);

        waveOut = new WaveOut(WaveCallbackInfo.FunctionCallback());

        waveOut.Init(baStream);

        waveOut.Play();

    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
        return;
    }
}

There is no reason to involve the thread pool here.