Error : Implementation for method missing (Delphi Prism)

I wrote my method: LangChange

type
  MainForm = partial class(System.Windows.Forms.Form)       
  private
开发者_StackOverflow中文版      ...
      method LangChange();
protected
    method Dispose(disposing: Boolean); override;
  public    
    constructor;
  end;
implementation
...
method LangChange();
begin
...    
end;

However,I have an error Error 1 (PE33) Implementation for method "Compiler.MainForm.LangChange" missing What is wrong?Help please!

LangChange is a method of the class MainForm so the implementation of the method should be

method MainForm.LangChange();
begin
end;