When would ShowDialog() return null?

Posted by Joe White on Stack Overflow See other posts from Stack Overflow or by Joe White
Published on 2009-06-13T06:16:39Z Indexed on 2010/03/18 4:41 UTC
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WPF's Window.ShowDialog method returns a nullable boolean. So does CommonDialog.ShowDialog.

Now, I understand cases where these would return false (user clicked Cancel or pressed Esc), and when they would return true (code sets Window.DialogResult to true, probably in response to OK being clicked). But null?

My first thought is that clicking the title bar's Close button might return null. But the docs state (and I confirmed by testing) that the title-bar Close button is treated as a Cancel.

So when would Window.ShowDialog or CommonDialog.ShowDialog ever return null?

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