WPF custom control or form inheritance problems that occur after inheritance cannot be the root of a XAML file

When we create Basewindow in WPF or want to inherit a custom UserControl, we often encounter errors such as "The root of a XAML file cannot occur after inheritance." The reason is that inheriting a class will flush out all the contents of the base class if the contents of the form are redefined:

Workaround: 1. Base class is set to inherit window or UserControl generic class file, do not create a file with XAML. or use custom controls to create their own ControlTemplate,

　　　　　

　　　　　2. Add the Oncontentchanged method to the inherited form or control, then fill in the contents of the base class form or control, and give an example:

Workaround:

WPF custom control or form inheritance problems that occur after inheritance cannot be the root of a XAML file