'InitializeComponent' does not exist in the current context WPF in Revit API

I created a class library (.NET Framework) project and then I added a new item in the project and selected WPF (.NET Framework) then the XAML file was created and the InitializeComponent() method was fine, but the problem pop up when I started to add the RevitAPI.dll and RevitAPIU.dll in the project references, the InitializeComponen() suddenly gives that error 'InitializeComponent' does not exist in the current context  I dunno why!
I searched on all the solutions on the internet but nothing helped about the Build Action and such things.
I hope someone can help with a radical solution since I spent 3 days in that error with all the solutions but it's still the same.

Thanks