When I navigate to another page in the NavigationView, it works, but when I try to return to the MainWindow by clicking on the selected item, it doesn't work.

Screenshot of the thrown exception:

Snippet

private void NavigationViewItem_Tapped(object sender, Microsoft.UI.Xaml.Input.TappedRoutedEventArgs e)
{
    rootframe.Navigate(typeof(MainWindow));
}

CodePudding user response：

You cannot navigate to the main window. Frame.NavigateTo() actually expects a "Page-derived data type". The documentation is especially muddy about it, but it finally states:

Causes the Frame to load content represented by the specified Page-derived data type,...

So, you need to create a new class deriving from Page, put your content there and that's it.