Strange behavior when showing WPF window in Outlook - wpf

Question

I use the following code to show my WPF window from the new message window in Outlook:
private void DisplayWindow(Window window) {
var wih = new System.Windows.Interop.WindowInteropHelper(window);
wih.Owner = GetForegroundWindow();
window.ShowInTaskbar = false;
window.ShowDialog();
}
[DllImport("user32.dll")]
private static extern IntPtr GetForegroundWindow();
My problem is that when ToolTips and ComboBox drop downs become visible, the WPF window disappears behind the new message window, leaving just the "popup" content in front. Could anyone explain why this might be happening, and what the correct way to host the window might be?
EDIT:
This only happens once a recipient has been added to the Send box and seems to only be a problem when the foreground window is the new mail message window.
To replicate:
Add an Outlook Add-in project and a WPF project (targeting .NET 4.0) to a new solution.
Put a ComboBox with a few items in it on the MainWindow.xaml.
Remove the StartupUri from App.xaml and add the following to App.cs.
public void ShowWindow() {
MainWindow window = new MainWindow();
var wih = new System.Windows.Interop.WindowInteropHelper(window);
wih.Owner = GetForegroundWindow();
window.ShowInTaskbar = false;
window.ShowDialog();
}
[DllImport("user32.dll")]
private static extern IntPtr GetForegroundWindow();
Add references to WindowsBase, System.Xaml and PresentationFramework to the Outlook project.
Add a Ribbon (XML) to the Outlook project with the following in the .xml.
<customUI ...>
<ribbon>
<tabs>
<tab idMso="TabNewMailMessage">
<group id="MyGroup"
insertAfterMso="GroupMailNew">
<button id="myButton"
size="large"
onAction="myButton_Action"
imageMso="HappyFace"/>
</group>
</tab>
</tabs>
</ribbon>
</customUI>
Add the following to the ribbon code.
MyWpfApplication.App app;
public void Ribbon_Load(Office.IRibbonUI ribbonUI) {
this.ribbon = ribbonUI;
var appThread = new Thread(new ThreadStart(() => {
this.app = new MyWpfApplication.App();
app.ShutdownMode = System.Windows.ShutdownMode.OnExplicitShutdown;
app.Run();
}));
appThread.SetApartmentState(ApartmentState.STA);
appThread.Start();
}
public void myButton_Action(Office.IRibbonControl control) {
// Dispatcher used as cross thread operation.
app.Dispatcher.BeginInvoke((Action)(() => {
app.ShowWindow();
}));
}
Add the following to ThisAddIn
protected override Microsoft.Office.Core
.IRibbonExtensibility CreateRibbonExtensibilityObject() {
return new Ribbon();
}
Run the Outlook add-in, create a new message, add a recipient and click on the smiley face button. You will see the bug when you click on the ComboBox.

Answer 1

Perhaps you are encountering the infamous "airspace" issue. See here, here and here. There were high hopes that it would be fixed in .NET 4.5, but sadly these were dashed when MS announced that the fix itself was too buggy to release.

Answer 2

It may be the same issue described here:
The WPF dialog box disappears when it displays a tooltip or drop-down combo box in Windows 8 or Windows Server 2012
Source codes of .NET Framework 4.7.1 have comment in System.Windows.FrameworkCompatibilityPreferences class, saying there is a bug in the Windows desktop window manager which can cause incorrect z-order for windows on some conditions.
The suggested workaround is to add the following code to the WPF application’s app.config file:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<appSettings>
<add key="UseSetWindowPosForTopmostWindows" value="True" />
</appSettings>
</configuration>