dogList 是方法 Main 的局部.您要做的是将 dogList 置于该范围之外.

dogList is local to the method Main. What you want to do instead is to place dogList outside of that scope.

public class Program
{
    static List<Dog> dogList = new List<Dog>();

...

或者，您可以将列表发送到您的 add 方法中.

Alternately you can send the list into your add method.