editors collection with DesignerSerializationVisibility

Question

Good evening all, I try to create a custom combobox with "user control" and set during the insertion property bar.

 

 

that's my main goal, but now I try to insert a custom combo box that lets me set through collection editors.

 

 

 

 

List<String> list = new List<String>();
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]

        public List<String> MyProperty { get { return list; } set { list = value; } }

 but when I want to add a new member it shows me this error message:

 

 

 

how to find a solution for this error?