I've got a routine that grabs a list of all images in a directory, then runs an MD5 digest on all of them. Since this takes a while to do, I pop up a window with a progress bar. The progress bar is updated by a lambda that I pass in to the long-running routine.

The first problem was that the progress window was never updated (which is normal in WPF I guess). Since WPF lacks a Refresh() command I fixed this with a call to Dispatcher.Invoke(). Now the progress bar is updated for a while, then the window stops being updated. The long-running work does eventually finish and the windows go back to normal.

I have already tried a BackgroundWorker and quickly became frustrated by a threading issue related to an event triggered by the long-running process. So if that's really the best solution and I just need to learn the paradigm better, please say so.

But I'd be really much happier with the approach I've got here, except that it stops updating after a bit (for example, in a folder with 1000 files, it might update for 50-100 files, then "hang"). The UI does not need to be responsive during this activity, except to report on progress.

Anyway, here's the code. First the progress window itself:

public partial class ProgressWindow : Window
{
    public ProgressWindow(string title, string supertext, string subtext)
    {
        InitializeComponent();
        this.Title = title;
        this.SuperText.Text = supertext;
        this.SubText.Text = subtext;
    }

    internal void UpdateProgress(int count, int total)
    {
        this.ProgressBar.Maximum = Convert.ToDouble(total);
        this.ProgressBar.Value = Convert.ToDouble(count);
        this.SubText.Text = String.Format("{0} of {1} finished", count, total);
        this.Dispatcher.Invoke(DispatcherPriority.Render, EmptyDelegate);
    }

    private static Action EmptyDelegate = delegate() { };
}


<Window x:Class="Pixort.ProgressWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Pixort Progress" Height="128" Width="256" WindowStartupLocation="CenterOwner" WindowStyle="SingleBorderWindow" ResizeMode="NoResize">
    <DockPanel>
        <TextBlock DockPanel.Dock="Top" x:Name="SuperText" TextAlignment="Left" Padding="6"></TextBlock>
        <TextBlock DockPanel.Dock="Bottom" x:Name="SubText" TextAlignment="Right" Padding="6"></TextBlock>
        <ProgressBar x:Name="ProgressBar" Height="24" Margin="6"/>
    </DockPanel>
</Window>

The long running method (in Gallery.cs):

public void ImportFolder(string folderPath, Action<int, int> progressUpdate)
{
    string[] files = this.FileIO.GetFiles(folderPath);

    for (int i = 0; i < files.Length; i++)
    {
        // do stuff with the file
        if (null != progressUpdate)
        {
            progressUpdate.Invoke(i + 1, files.Length);
        }
    }
}

Which is called thusly:

 ProgressWindow progress = new ProgressWindow("Import Folder Progress", String.Format("Importing {0}", folder), String.Empty);
 progress.Show();
 this.Gallery.ImportFolder(folder, ((c, t) => progress.UpdateProgress(c, t)));
 progress.Close();