Partial declarations of must not specify different base classes
I wanted to use a common base class for a set of UserControls in my WPF application, but when I changed the class’s ancestor in the code file and compiled I would get the error “Partial declarations of must not specify different base classes” This is because when you compile a WPF application Visual Studio generates a partial class in a code-behind file automatically, the base type specified is always “UserControl”. To solve this problem change your XAML from this < UserControl x:Class ="MyApp.MyControl" /> To this < local:SomeBaseTypeYouWantToUse x:Class ="MyApp.MyControl" xmlns:local ="clr-namespace:NameSpace.To.Your.BaseClass" />