通过查看你提供的错误，似乎函数是在类边界之外定义的（检查你的括号）。



任何函数都应该只定义在类委托，枚举，接口或结构的边界内。

By looking into error you provided it seems that the function is defined outside the class boundary(check your parentheses).

Any function should be defined only inside the boundaries of class delegate, enum ,interface or struct.

您是否添加了System.Data命名空间？



我认为你错过了这个名称空间。

Have you added System.Data namespace?

I think you are missing this namepace.

using System.Data;

添加上面的命名空间并检查。

Add the above namespace and check.