WPF BackGroundWorker ProgressChanged not updating textblock - wpf

Question

I have the method below that seems to behaving strangely. The ProgressChanged and RunWorkerCompleted seem to be updating themselves at the same time. If I comment out the RunWorkerCompleted code which updates the textblock I see the ProgressChanged taking effect after the data is transferred. What am I doing wrong here? I obviously want the textblock to show I'm getting data, then change when I have finished getting the data.
public void GetAppointmentsBackground()
{
System.Windows.Threading.Dispatcher webServiceDispatcher = this.Dispatcher;
worker = new BackgroundWorker();
worker.WorkerReportsProgress = true;
worker.DoWork += delegate(object sender, DoWorkEventArgs args)
{
GetAppointmentsForDayDelegate getAppt = new GetAppointmentsForDayDelegate(GetAppointmentsForDay);
webServiceDispatcher.BeginInvoke(getAppt);
(sender as BackgroundWorker).ReportProgress(25);
};
worker.ProgressChanged += delegate(object s, ProgressChangedEventArgs args)
{
txtMessages.Text = "Contacting Server";
};
worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args)
{
txtMessages.Text = "Completed Successfully";
};
worker.RunWorkerAsync();
}

Answer 1

In fact, the thing is that another model is used for System.Windows.Controls (differs from Windows.Forms.Control descendants).
I used something like:
public delegate void NoArgs();
//...
txtBlock.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Normal,
new NoArgs(UpdateTextBlock));
//...
void UpdateTextBlock()
{
txtBlock.Text = "Contacting Server";
}
Read the manual about Dispatcher and DispatcherObject for the purpose.

Answer 2

I would suggest you wrap this up in a try{...}catch block... and a using clause, as shown below
public void GetAppointmentsBackground()
{
System.Windows.Threading.Dispatcher webServiceDispatcher = this.Dispatcher;
try
{
using (BackgroundWorker worker = new BackgroundWorker())
{
worker.WorkerReportsProgress = true;
worker.DoWork += delegate(object sender, DoWorkEventArgs args)
{
GetAppointmentsForDayDelegate getAppt = new GetAppointmentsForDayDelegate(GetAppointmentsForDay);
webServiceDispatcher.BeginInvoke(getAppt);
(sender as BackgroundWorker).ReportProgress(25);
};
worker.ProgressChanged += delegate(object s, ProgressChangedEventArgs args)
{
txtMessages.Text = "Contacting Server";
};
worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args)
{
if (txtMessages.InvokeRequired)
{
txtMessages.BeginInvoke(new MethodInvoker(delegate()
{
txtMessages.Text = "Completed Successfully";
}));
}
else
{
txtMessages.Text = "Completed Successfully";
}
};
worker.RunWorkerAsync();
}
}
catch(Exception eX)
{
/* CHECK HERE TO SEE IF AN EXCEPTION IS THROWN */
}
}
If there is no exception thrown, perhaps using an BeginInvoke method of the txtMessages class as shown above in the RunWorkerCompleted event handler, as there may be a cross-threading error when trying to update the txtMessages itself from the backgroundworker class.