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POVery strange behavior with WinForms ListBox and Ctrl+C keypress
 

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  1. POVery strange behavior with WinForms ListBox and Ctrl+C keypress
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    <p>I'm experiencing some very strange behavior in a WinForms <code>ListBox</code> in two of my applications. They both have some other controls (<code>TableLayoutPanel</code>s, <code>Button</code>s, etc.)</p> <p>Both applications handle the Ctrl+C keystroke to copy the selected item(s) of the <code>ListBox</code> to the clipboard. When I press Ctrl+C, though, the selected index of the current <code>ListBox</code> moves down by one, or if the last item is selected, the selection wraps around to the first item. This happens <em>after</em> my <code>KeyDown</code> handler does its work.</p> <p>This is very strange because there's no code in either application that would cause this behavior. I don't even know what key to press to make the selection advance or wrap like that.</p> <p>I've been trying to reproduce this behavior in a sample program, but so far I haven't been able to figure out what these two applications have in common that makes them behave this way. If I figure it out, I will update this question accordingly.</p> <p>I compared the Windows message activity between an application that has this problem and an application that doesn't. I found one specific message that is causing it:</p> <pre><code>msg=0x2111 (WM_REFLECT + WM_COMMAND) hwnd=0x211e2 wparam=0x111e2 lparam=0x211e2 result=0x0 </code></pre> <p>Here are the full message logs from pressing Ctrl+C in each program:</p> <ul> <li>Message log WITH this problem: <a href="https://gist.github.com/2854221" rel="nofollow">https://gist.github.com/2854221</a></li> <li>Message log WITHOUT this problem: <a href="https://gist.github.com/2854203" rel="nofollow">https://gist.github.com/2854203</a></li> </ul> <p>I can prevent this mystery message from being handled, but what is it, and what causes it to be sent? I'm stumped.</p>
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    1. CODid you try to add a temporary event handler to the ListBox.SelectedIndexChanged event to see which code changed the selection?
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      1. USUranus
    2. COYes... it's in native code and the `base.WndProc` method. I have something better though - I just updated the question with the exact Windows message that causes the behavior.
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