How do I display progress during a busy loop?

Question

I have a loop that reads plenty of data from an external source. The process takes about 20 seconds, and I want to show the progress to the user. I don't need any fancy progress bars, so I chose to plot my progress in a label that will say "Step 1/1000", then change to "Step 2/1000" etc.

My code looks something like this:

// "count" is the number of steps in the loop, 
// I receive it in previous code

String countLabel = "/"+count.ToString();

for (i = 0; i < count; i++)
{
    ... do analysis ...
    labelProgress.Content = "Step "+i.ToString()+countLabel
}

However, during that analysis the screen is "stuck" and the progress does not show as advancing. I understand this behavior from my past in C++, where I would probably have a separate thread showing a progress bar receiving notifications from the loop, or some form of repaint/refresh, or forcing the window/app to process its message queue.

What's the right way to do it in C#? I'm not tied to the label, so if there's a simple progress-bar popup screen I could use instead of this label it would also be great...

Thanks

Answer 1

Move the work to a BackgroundWorker and use the ReportProgress method.

for (i = 0; i < count; i++)
{
    ... do analysis ...
    worker.ReportProgress((100 * i) / count);
}

private void MyWorker_ProgressChanged(object sender,
    ProgressChangedEventArgs e)
{
    taskProgressBar.Value = Math.Min(e.ProgressPercentage, 100);
}

Answer 2

    //Create a Delegate to update your status button
    delegate void StringParameterDelegate(string value);
    String countLabel = "/" + count.ToString();
    //When your button is clicked to process the loops, start a thread for process the loops
    public void StartProcessingButtonClick(object sender, EventArgs e)
    {
        Thread queryRunningThread = new Thread(new ThreadStart(ProcessLoop));
        queryRunningThread.Name = "ProcessLoop";
        queryRunningThread.IsBackground = true;
        queryRunningThread.Start();
    }

    private void ProcessLoop()
    {
        for (i = 0; i < count; i++)
        {
            ... do analysis ...
            UpdateProgressLabel("Step "+i.ToString()+countLabel);
        }
    }

    void UpdateProgressLabel(string value)
    {
        if (InvokeRequired)
        {
            // We're not in the UI thread, so we need to call BeginInvoke
            BeginInvoke(new StringParameterDelegate(UpdateProgressLabel), new object[] { value });
            return;
        }
        // Must be on the UI thread if we've got this far
        labelProgress.Content = value;
    }

Answer 3

The UI is not updated due to the fact that your current thread has a higher priority than your UI thread which will ultimately set the label ;). So until your thread has finished to your stuff it will update your label in the end.

Lucky for us, there is a Dispatcher property on every WPF control that lets you fire up a new thread with another priority..

labelProgress.Dispatcher.Invoke(DispatcherPriority.Background,
                    () => labelProgress.Content = string.Format("Step {0}{1}", i, countLabel));

This fire up a thread in the background and would get the job done! You can also try other DispatcherPriority options

PS I also took the liberty to add an anonymous method and fix your string parsing somewhat.. hope you don't mind..