继承与方法重写

  public class A
    {
        public virtual void Fun1(int i)
        {
            Console.WriteLine(i);
        }

        public void Fun2(A a1)
        {
            a1.Fun1(1);
            Fun1(5);
        }
    }

    public class B : A
    {
        public override void Fun1(int i)
        {
            base.Fun1(i + 1);
        }
    }

    class Program
    {
        public static void Main()
        {
            B b = new B();
            A a = new A();
            a.Fun2(b);
            b.Fun2(a);

            Console.ReadKey();
        }
    }

输出结果是

A a = new A(); 

B b = new B();

 a.Fun2(b);      将子类B的实例b作为参数传递给父类A的引用a1。Fun2的this是父类的实例a

a1.Fun1(1); 输出2      因为父类的变量a1里实际存储的是子类的实例b，所以这里调用的是子类Fun1

Fun1(5);      输出5       这里的调用，是this.Fun1(5)。而这里的this是a，所以调用的是父类的Fun1

b.Fun2(a);       将父类A的实例作为参数传递，Fun2的this是b

a1.Fun1(1);  输出1         因为父类的变量a1里实际存储的是父类的实例a，所以这里调用的是父类的Fun1

Fun1(5)       输出6         这里的调用是this.Fun1(5);而这里的this是b,所以这里调用的是子类的Fun1

需要留意的是类A中的Fun2方法，在里面调用Fun1的时候，相当于是this.Fun1

ps：如果把B中的override改为new的话，输出的结果：

1

5

1

5

https://www.c-sharpcorner.com/article/understanding-method-overriding-and-virtual-override-and-new-keywords-in-c-sharp/

For example - I have a base class Fruit with a function Details(). There is another class Mango which inherits Fruit but also has a function named Details().

    public class Fruit  
    {  
    public void Details()  
    {  
    }  
    }  

    public class Mango : Fruit  
    {   
    public void Details()  
    {  
    }  
    }  

As per the overriding principle, an object of Fruit can call Details() of Fruit, if it stores the instance of Fruit.

The object of Fruit can call the method- Details of class Mango, if it stores the instance of class Mango.

Fruit a = new Fruit();  
a.Details();    // Calls the method- Details of base class Fruit  
a = new Mango();  
a.Details();    // Calls the method- Details of derived class Mango 

Ok, so we learned what is overriding.