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Friday, June 12, 2009

Crossing Thread Boundaries

Sometimes you find a solution to a problem and you just add it to your Swiss Army Knife of code to handle similar problems down the road.  If you’ve ever used a Timer on a WinForms application, you’ve likely run into the following error message:

Cross-thread operation not valid: Control 'someControl' accessed from a thread other than the thread it was created on.

Since .Net 2.0 I’ve run the same game strategy for hopping back over to the UI thread when I want to make updates.  Basically, I make a delegate with the appropriate parameters to handle whatever update I want (like strings for the Text property on a Lable), then check InvokeRequired to re-call the method, if necessary.

But I’ve been neglecting a good friend: anonymous delegates.

Today I came across an article related to something entirely different and they mentioned ‘MethodInvoker’.  This turns out to be a very clean implementation.  Because the anonymous delegate gets the scope variables of the method it’s created in, you don’t have to pass parameters, nor do you have to re-call the same method.

The end result – sans named delegate – looks elegantly like the following example:

void CoordsReceived(object sender, CoordinatesReceivedEventArgs e)
this.Invoke(new MethodInvoker(delegate()
lblLattitude.Text = e.Lattitude.ToString();
lblLongitude.Text = e.Longitude.ToString();

Still very readable, arguably more so, and still takes care of getting back on the right thread to update the UI.

I can’t believe I missed this for so long…all those delegates!

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