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PODetermine when a mouse hook has handled the last message
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  1. PODetermine when a mouse hook has handled the last message
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    copied!<p>I have a form, that acts like a drop-down, that I display non-modal. I attach a mouse hook to the form to determine when the mouse is clicked out of it, so that I know to close it - by setting <code>Visible = False</code>.</p> <p>Because I want the <code>HookProc</code> to handle the last click, I can't dispose the Hook or my Dropdown until I'm sure that my event handler has returned to the HookProc.</p> <p>It's a bit hard to explain, but I hope the code below makes it a little clearer:-</p> <pre><code>//Loop to display the dropdown. Dim dd as New DropDown dd.Visible = True Do While dd.Visible Application.DoEvents() NativeMethods.MsgWaitForMultipleObjectsEx(0, IntPtr.Zero, 250, &amp;HFF, 4) Loop // I want to dispose dd now, but how can I be sure that e.Handled (See below) // has been returned to HookProc? //A handler within dropdown to determine what to do with the mouse click. Private Sub DropDown_MouseHookClick(ByVal sender As Object, ByVal e As MouseClickEventArgs) If IWantToCloseTheDropDown Then e.Handled = True MyHook.UnHook Me.Visible = False End If // All done, e.Handled is returned to HookProc. // But which happens first? Will e.Handled arrive at HookProc first, or will // the form display loop, above, notice that Visible is now False? End Sub //The main part of the hooking class. Public Function MouseHookProc(ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer Dim MyMouseHookStruct As MouseHookStruct = DirectCast(Marshal.PtrToStructure(lParam, GetType(MouseHookStruct)), MouseHookStruct) If nCode &lt; 0 Then Return CallNextHookEx(hHook, nCode, wParam, lParam) Else Dim handle As Integer = MyMouseHookStruct.hwnd Dim c As Control = Control.FromHandle(New IntPtr(handle)) If MouseUpOrDown Then Dim e As MouseHookClickEventArgs OnMouseClick(e) If e.Handled Then Return 1 EndIf End If Return CallNextHookEx(hHook, nCode, wParam, lParam) End If End Function </code></pre>
 

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