Problems after copying XAML controls from WPF Application to a class library

Question

In the process of refactoring some code, I encountered several build errors such as these:

Library project file cannot specify ApplicationDefinition element.

Answer 1

You may also see this even though your build actions are set correctly. For example, if you start your project up as an Application, and then later switch it to be a Class Library. In which case you must also remember to delete App.xaml (and the corresponding App.cs).