The class Form1 can be designed, but is not the first class in the file.

The class Form1 can be designed, but is not the first class in the file. Visual Studio requires that designers use the first class in the file. Move the class code so that it is the first class in the file and try loading the designer again.

原 因，我在Form1.class中多加了一个class，且放在了public partial class Form1 : Form之前。

解 决方法，将那个class放在public partial class Form1 : Form之后。