您不能在运行时更改类定义.但是，您可以创建一个继承自原始类的新类(如果它不是 sealed)并声明该字段.您可以通过使用 System.Reflection.Emit 发出适当的 IL 代码来实现这一点.

You can't alter a class definition at runtime. However, you can create a new class that inherits from the original class (if it's not sealed) and declares the field. You can do this by emitting the appropriate IL code using System.Reflection.Emit.