To start the application in full screen mode, try installing ApplicationView.PreferredLaunchWindowingMode already in the App.xaml.cs constructor
public App() { ApplicationView.PreferredLaunchWindowingMode = ApplicationViewWindowingMode.FullScreen;
To have a button that toggles full screen, do
var view = ApplicationView.GetForCurrentView(); if (view.IsFullScreenMode) { view.ExitFullScreenMode(); } else { view.TryEnterFullScreenMode(); }
However, I need to add that even without specifying any of the above code, when you open the application in a Windows 10 tablet or Windows 10 desktop with tablet mode turned on, the application will automatically maximize itself to full screen.
While your application is available on Windows 10 desktop devices, I would recommend that you do not install it in full screen mode at startup, because UX will be much easier for desktop users to work with windowed applications.
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