Expect the Unexpected

I was working on our Silverlight4 app today, coding up a child window. I created the child window from a given page, add an event handler for the Closing event, and opened the window. I tested in the debugger.

Once I was done in the window, I clicked the OK button. Imagine my surprise when the string I was trying to retrieve was empty. I had tested the window under the debuger, and had already verified that it was setting the string property, but the parent page was getting back an empty string. Enter, the Debug.WriteLine() method.

What I found was shocking. It turns out that the OK button handler was indeed being hit, but before the method exited, the window's Closed and Closing events were firing - BEFORE the OK handler was done with its processing.

The problem was that I had placed the following code at the TOP of the OK click handler:

this.DialogResult = true;

When I moved it to the bottom of the click handler (after all of the processing was done), the events fired in the expected order and at the expected time.

The tip is never make assumptions about how the framework works. I can't recall this being an issue in Windows Forms apps, but it certainly made itself known while I was working in Silverlight.

Be careful out there.

EDIT =============

Changed tags to be more appropriate