错误信息是这样,要声明一下怎样声明呢???
E:\visual studio\Form2.cs(228): The type or namespace name 'ReturnEventArgs' could not be found (are you missing a using directive or an assembly reference?)
E:\visual studio\Form2.cs(228): The type or namespace name 'ReturnEventArgs' could not be found (are you missing a using directive or an assembly reference?)