How to: Extract to Interface (C# only)
You can extract one or more public members from a type into a new interface.
To extract members to a new interface
In Class Designer, right-click the type that contains the member or members you want to extract, point to Refactor, and click Extract Interface.
The Extract Interface dialog box displays default values for the name of the interface and the name of the code file in which it will be declared. Either accept the default values or change them.
In the Select public members to form interface pane, select or clear the check box next to the members you want to extract into the new interface, and click OK.
A new interface is created, and the file that houses it is added to the project.