Native Window: Release Handle On Close

Question

I am currently working on a C# .NET Add-In for Microsoft Outlook. The goal of the Add-In is, to capture the search input from the Outlook Instant Search, and show in a Custom Pane my own search results.

It works pretty well, and with subclassing the Outlook Window with a Native Window, I get the search string, and it already passes that into my panel.

The problem is now, that when you close the Add-In (via "File->Options->Add-Ins->COM Add-Ins", but not with the X in the pane), the Add-In gets terminated instantly and I can't call searchboxWindow.ReleaseHandle() beforehand to restore my WndProc chain. Outlook simply crashes without any visible errors.

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);

    switch ((uint)m.Msg)
    {
        case WindowMessages.WM_DESTROY:
        case WindowMessages.WM_QUIT:
        case WindowMessages.WM_NCDESTROY:
            this.ReleaseHandle();
            return;

        case WindowMessages.WM_KEYUP:
        case WindowMessages.WM_LBUTTONDOWN:
        case WindowMessages.WM_RBUTTONDOWN:
            OnKeyUp();
            break;

        case WindowMessages.WM_EXITSIZEMOVE:
            OnResize();
            break;
    }
}

I already tried to listen to a few Window Messages that should be called when the Add-In gets closed, but these messages only appear when I close the Outlook in a normal way.

Also, the events in the main Add-In source file like AppDomain.CurrentDomain.ProcessExit, this.Shutdown, or ((Outlook.ApplicationEvents_10_Event)this.Application).Quit don't get called.

What event can I listen on that (reliably) gets fired when the Add-In is terminated? Are there some? If not, what alternatives to solve my problem do I have?

Did you try Dipose(), and attaching a method to the Diposed event to make sure it actually did get disposed? — Mr. B, Aug 11 '15 at 15:19
I implemented the IDisposable interface and called the ReleaseHandle() in there, but it had no effect? Is that what you mean? — Florian Schöffl, Aug 11 '15 at 15:24
Use your add-in's Shutdown event to un-subclass the window. The auto-generated ThisAddIn_Shutdown() event handler has scary language but it is still raised in this specific scenario. — Hans Passant, Aug 11 '15 at 16:37
"Starting in Outlook 2010, Outlook, [...] no longer calls the ThisAddin_Shutdown method when Outlook is shutting down." [source](https://msdn.microsoft.com/en-us/library/office/ee720183(v=office.14).aspx#OL2010AdditionalShutdownChanges_AddinShutdownChangesinOL2010Beta) - You sure that it is called in this case? I can't check right now — Florian Schöffl, Aug 11 '15 at 16:40
This may be one of the rare situations where you might need to implement a finalizer. Take a look at this article https://limbioliong.wordpress.com/2011/07/03/invoking-finalizers-of-net-based-com-objects-in-an-unmanaged-app-part-1/ — Scott Chamberlain, Aug 11 '15 at 21:14

score 1 · Accepted Answer · answered Aug 14 '15 at 06:48

1

SOLVED: Thanks to Hans Passant

It realy seems that the ThisAddIn_Shutdown Event is triggered when the Add-In is manually disconnect through the COM Add-ins dialog box.

answered Aug 14 '15 at 06:48

Florian Schöffl

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score 0 · Answer 2 · edited Aug 11 '15 at 20:30

0

I don't think there is much you can do in the managed code. Unmamaged code would have worked fine; the COM system would ask you politely whether your dll can be unloaded by calling your implementation of DllCanUnload.

edited Aug 11 '15 at 20:30

Wandering Fool

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answered Aug 11 '15 at 16:18

Dmitry Streblechenko

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So basicly i can't do anything until i rewrite my project in c++ or similar? – Florian Schöffl Aug 11 '15 at 16:25

score 0 · Answer 3 · answered Apr 01 '19 at 22:40

0

Make sure you add a DWORD RequireShutdownNotification=1 in your addin registry, otherwise ThisAddIn_Shutdown() will not be called

answered Apr 01 '19 at 22:40

Alex

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Native Window: Release Handle On Close

3 Answers3