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POHow do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
 

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  1. POHow do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
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    <p>Earlier I asked <a href="https://stackoverflow.com/questions/542392/how-can-i-cancel-a-users-wpf-treeview-click">how to cancel a WPF TreeViewItem.Selected event</a>.</p> <p>The answerers suggested I instead handle the PreviewMouseDown event before the selection even takes place. That makes sense.</p> <p>I've tried to do that...</p> <p>XAML...</p> <pre><code>&lt;TreeView Name="TreeViewThings" ... PreviewMouseDown="TreeViewThings_PreviewMouseDown" TreeViewItem.Expanded="TreeViewThings_Expanded" TreeViewItem.Selected="TreeViewThings_Selected" &gt; </code></pre> <p>Visual Basic...</p> <pre> Sub TreeViewThings_PreviewMouseDown(...) If UnsavedChangesExist() Then e.Handled = UserCancelled() Else e.Handled = False End If End Sub Function UnsavedChangesExist() As Boolean ... End Function Function UserCancelled() As Boolean Return MessageBox.Show("Discard your unsaved changes?", _ "Unsaved Changes", _ MessageBoxButton.OKCancel, _ MessageBoxImage.Question) = MessageBoxResult.Cancel End Function </pre> <p>This is only sort of working...</p> <ul> <li>If there are no unsaved changes, then it proceeds just fine and executes TreeViewThings_Selected().</li> </ul> <p>If there are unsaved changes, then I see the MessageBox...</p> <p><a href="http://img25.imageshack.us/img25/141/discard2yk0.gif" rel="nofollow noreferrer">MessageBox: Continue and discard your unsaved changes? OK/Cancel http://img25.imageshack.us/img25/141/discard2yk0.gif</a></p> <ul> <li><p>If I then choose Cancel, it cancels.</p></li> <li><p>However, If I instead choose OK to discard my unsaved changes, then it just cancels anyway--even though e.Handled = False. It does not continue on and execute TreeViewThings_Selected().</p></li> </ul> <p>I think the fact that there's a MessageBox screws it up somehow.</p> <p>What am I doing wrong?</p>
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    1. USZack Peterson
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      1. POHow do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
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    1. COHave you stepped through your preview mouse down handler in the debugger to see if it is working as you expected? You should be able to see if e.Handled is being set to true/false and when. If it is, you know there is a problem with the box.
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      1. POHow do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
      1. USJosh G
    2. COI have stepped through with the debugger. e.Handled is getting set as expected. I don't know why, but the MessageBox itself seems to be the problem.
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      1. POHow do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
      1. USZack Peterson
    3. COI've asked a follow-up question: http://stackoverflow.com/questions/546388/wpf-does-messagebox-break-previewmousedown
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      1. POHow do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
      1. USZack Peterson
 

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