Q:

C# WPF How to close a new window correctly?

I have a simple question:

Create a new WPF project, there's startup window in it(MainWindow.xaml).
in this project, create a new Window(Window1.xaml)
Windows1's loaded event, let it close:
private void Window_Loaded(object sender, RoutedEventArgs e)
{
    this.Close();
}
put a "Open" button to MainWindow, implement it's click event:
private void button_Click(object sender, RoutedEventArgs e)
{
    Window1 w = new Window1();
    w.Show();
}

when I start this application, VS2015's UI became to the 'DEBUGING MODE', then I click the close button on the right top corner of the Window, VS2015's UI back to normal mode.
now, if I start application, click "Open" button, then Window1 will show quickly and closed, but, if I click the close button on the right top corner of MainWindow, things different: VS2015 will no go back to normal mode but stay in 'DEBUGING MODE'. so to me, that means something hang there and I don't know what is it.
is there anyone know how to fix this problem?

A:

This is not an answer, but just my findings of an actually interesting observation. I did your test (opening and closing the Window) a couple times and then dumped the list of WPF windows:
foreach (Window w in Application.Current.Windows)
    Debug.WriteLine(w.GetType().FullName)

Resulting in:
WpfTest.MainWindow
Microsoft.VisualStudio.DesignTools.WpfTap.WpfVisualTreeService.Adorners.AdornerLayerWindow
Microsoft.VisualStudio.DesignTools.WpfTap.WpfVisualTreeService.Adorners.AdornerLayerWindow
Microsoft.VisualStudio.DesignTools.WpfTap.WpfVisualTreeService.Adorners.AdornerLayerWindow

WpfTap is Visual Studio's WPF debugger, that helps debug the WPF content tree.
Now, if instead of using the Loaded event, I used the ContentRendered event to close the window, it doesn't happen, and things work as normal.  It's also fine if I run the .exe without debugging.
So it seems like Visual Studio attaches the WPF debugger *after* a Window's Loaded event, and if you close the window too early, it leaves the debugger component hanging around in memory.

A:

In the App.xaml set:
ShutdownMode="OnMainWindowClose"

This must solve the problem. I recommend reading this question.

