You are creating a partial class, so you probably have these members defined in another source file for your partial class.
You may look at the solution explorer, find that source file and either remove it from there or you may remove these members from your current partial class.
You may see: Partial Classes and Methods (C# Programming Guide)
To search for the other source file containing the partial class, right click on the Class Name AddPage
and select Go to Definition
. You will see multiple results in Find Symbol result window in visual studio.