The class foo can be designed, but is not the first class in the file error

Question

I have this

The class foo can be designed, but is not the first class in the file

error after adding foo class derived from TextBox

Answer 1

Either your class.Designer.cs file OR your class.cs file will have another class defined at the top of it. Since the class is defined in both files as a partial class be sure to check both of the files!