Question

In a WPF app I have a sheduled database access task, periodically run by a timer and this task have been executed in a BackgroundWorker thread.

When connection attempt failed I raise an exception by try_catch construction and I want to update a Status Bar text in a UI thread.

Is there some prebuild event construction in a BackgroundWorker for implementing this, something like DoWorkEventHandler or RunWorkerCompletedEventHandler, which can be used for this? If not, how to do it better?

Edited (added):

If I want to handle the exception inside RunWorkerCompletedEventHandler, using e.Error parameter, it doesn’t work. In case I leave exception unhandled in the BackgroundWorker thread, application hangs on and debugger points to the string of code which is excuted inside BackgroundWorker thread, saying that: Exception was unhandled by user code.

So, in this case, thread doesn’t just stop, signalling to RunWorkerCompletedEventHandler that it stopped with error, but the whole application stop working.

Answer 1

A WPF UI can be updated from a background thread by using Dispatcher.BeginInvoke.

For example if your background code was part of a Window then you could update a TextBlock:

this.Dispatcher.BeginInvoke((Action)(() =>
    {
        textBlock.Text = "Connection Failed!";
    }));

Edit:

If your background code were in a class other than your Window you could make an interface to help:

public interface IShowStatus
{
    void ShowStatus(string message);
}

Implement the interface in your Window

public void ShowStatus(string message)
{
   this.Dispatcher.BeginInvoke((Action)(() =>
       {
           textBlock.Text = message;
       }));
}

In your class with the background worker make a property to hold a reference to the interface.

public IShowStatus StatusDisplay { get; set; }

In your Window class initialize the background class.

public void InitBackground()
{
    BackgroundClass background = new BackgroundClass();
    background.StatusDisplay = this;
    ...

Finally in your background thread you can say:

StatusDisplay.ShowStatus("Connection Failed!");