Question

I am building a WPF application that calls web services and displays the data returned from the service after being broken down and analyzed by my application. The problem that I am facing is with multithreading. One of the API calls is made using a DispatcherTimer every 60 seconds. The issue is that when this event fires, it blocks the UI thread. I have attempted (in all ways that I can think) to update the UI from the background thread using BackgroundWorker and Dispatcher objects (also delegates) and I cannot figure this out. I need an example showing a label on the UI thread being updated by the background thread. Any help with this would be fantastic as I am about to freak out :).

I have looked at the other articles and it is just not making a terrible amount of sense to me. Please, bear with me as I am pretty new to this. Here is an example of what I would like to do. I have a label on the window named lblCase. I call pullData() every 60 seconds and I want to update lblCase with the returned data without blocking the UI.

private void pullData()
{
  //API call goes here...
  lblCase.Content = iCase;
}

public MainWindow()
{
    InitializeComponent();
    DispatcherTimer timer = new DispatcherTimer();
    timer.Tick += new EventHandler(timer_Tick);
    timer.Interval = new TimeSpan(0,0,60);
    timer.Start();
}

private void timer_Tick(object sender, EventArgs e)
{
  pullData();
}

Answer 1

Have a look at this question…

cheers,

EDIT:

Joe – not sure if you’re getting any closer to groking this, so I thought I’d try to put together a simple usage of BackgroundWorker to demonstrate how simple and powerful this class is!

first – in your constructor…

public MainWindow()
{
    InitializeComponent();

    BackgroundWork worker = new BackgroundWorker();
    worker = new BackgroundWorker();
    worker.DoWork += new DoWorkEventHandler(worker_DoWork);
    worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);

    System.Timers.Timer t = new System.Timers.Timer(10000); //  10 second intervals
    t.Elapsed += (sender, e) =>
    {
        // Don't try to start the work if it's still busy with the previous run...
        if (!worker.IsBusy)
            worker.RunWorkerAsync(); };
    }
}

so we have set up something to delegate some work (in the method ‘worker_DoWork’) on a background thread… whatever happends in that method will not impact the UI thread, and it should look something like:

private void worker_DoWork(object sender, DoWorkEventArgs e)
{
    // Whatever comes back from the lengthy process, we can put into e.Result
    e.Result = DoMyBigOperation();
}

Now when this thread completes, it will fire the RunWorkerCompleted event, which we have handled as such:

private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // First, handle the case where an exception was thrown.
    if (e.Error != null)
    {
    // handle the System.Exception
        MessageBox.Show(e.Error.Message);
    }
    else if (e.Cancelled)
    {
        // now handle the case where the operation was cancelled... 
        lblCase.Content = "The operation was cancelled";
    }
    else
    {
        // Finally, handle the case where the operation succeeded
        lblCase.Content = e.Result.ToString();
    }
}

Hope this helps!
IanR