UI behaves differently when I am debugging in Visual Studio

Question

I have some drag and drop functionality I am using in an xceed grid. When I try to drag and item down just one row, it doesn't work. But if I put a break point in my drop method and do the drop then, it has changed when I come back to the UI. What might cause it to behave differently whether I break into the code or not?

Answer 1

If you "pause" your application using a debugger breakpoint, the state of the system (e.g. mouse button state) can change while it's paused, and thus be different when you allow the program to continue running. This can cause a very different behaviour than if the program were running normally. As a result of this, debugging drag and drop problems using breakpoints is often impossible.

In these situations a good approach is often to go back to basics and use a Debug.WriteLine (or similar) to dump useful information about the state of your variables as it runs "normally" (instead of killing it with a breakpoint). Then you can examine this dumped information at your leisure after the program has finished the drag, in order to work out what was happening at each stage in the process and work out why it failed.