Closing Settings dialog causes application to quit - wpf

Question

So here's the setup. I have a standalone WPF application which I've built with VB. Contained in the application is two windows, MainWindow and SettingsWindow, which opens as a dialog and is called from a subprocedure in MainWindow.xaml.vb on the event of a clicked "Settings" button (I like working with code-behind much better than XAML if I can help it).
In SettingsWindow.xaml.vb, I have a subprocedure handling the event of clicking a close button in the window. It executes Me.Close(). The intent is to close SettingsWindow and return focus to MainWindow, but instead, the entire application terminates.
Additionally, clicking the close button in MainWindow closes MainWindow, but doesn't terminate the application in Visual Studio's debug mode, while closing SettingsWindow does.
When building the application and running it outside of Visual Studio (running the .exe itself in Windows), closing SettingsWindow returns to MainWindow as intended, but attempting to re-open SettingsWindow causes the entire application to crash.
I'm relatively new to Visual Studio, and I can post code as needed. Thanks ahead of time for the help.
First, here is my `Application.xaml.vb' file handling app startup:
Class Application
Public Shared initmain As MainWindow = New MainWindow()
Public Shared Sub AppStart() Handles Me.Startup
initmain.UpdateSettings()
initmain.Show()
End Sub
End Class
The code above checks My.Settings, which works fine, then calls MainWindow open.
Here is the code in the MainWindow sub calling SettingsWindow:
Private Sub SettingStart() Handles SettingsButton.MouseUp
Dim SettingWin As SettingsWindow = New SettingsWindow()
' "If" blocks here that check My.Settings before opening the window
SettingWin.ShowDialog()
End Sub
Finally, here is the code that closes SettingsWindow:
Private Sub CloseButtonClick() Handles CloseButton.MouseUp
Me.Close()
End Sub
If you need it, here is Application.xaml:
<Application x:Class="Application"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Startup="AppStart">
<Application.Resources>
</Application.Resources>
</Application>
Update:
It looks like the issue has to do with the fact that the instance of MainWindow in Application.xaml.vb is Public Shared, but I need to be able to call to that instance from other places to update settings in realtime, so I can't change this. Workarounds?
Additionally, the program now functions properly outside of Visual Studio, no longer crashing.

Answer 1

You need to set the ShutdownMode="OnLastWindowClose" in Application.xaml
<Application x:Class="Application"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml"
ShutdownMode="OnLastWindowClose" >
<Application.Resources>
</Application.Resources>
</Application>
MainWindow.xaml.vb
Class MainWindow
Private Sub ButtonSetting_Click(sender As Object, e As RoutedEventArgs) Handles ButtonSetting.Click
Dim SettingWin As SettingWindow = New SettingWindow()
Dim rslt As Boolean = False
rslt = SettingWin.ShowDialog()
End Sub
End Class