CLR call Virtual Methods

最新推荐文章于 2024-12-11 17:26:30 发布

lyso2008

最新推荐文章于 2024-12-11 17:26:30 发布

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分类专栏： C# 文章标签： methods class output string object c#

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本文探讨了CLR通过callvirt指令调用实例方法的规则，包括如何调用虚拟实例方法和非虚拟实例方法，并通过两个具体示例展示了多态调用的过程及输出结果。

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CLR via C# has following rules:

The callvirt IL instruction can be used to call instance and virtual methods, not static methods. When the callvirt instruction is used to call an instance or virtual method, you must specify a variable that refers to an object. When the callvirt IL instruction is used to call a nonvirtual instance method, the type of the variable indicates which type defines the method that the CLR should call. When the callvirt IL instruction is used to call a virtual instance method, the CLR discovers the actual type of the object being used to make the call and then calls the method polymorphically.

Take a look at following two examples:

Example1.

    class BaseClass
    {
        internal void TestMethod1()
        {
            Console.WriteLine("BaseMethod1");
            TestMethod2();
        }

        internal virtual void TestMethod2()
        {
            Console.WriteLine("BaseMethod2");
        }
    }

    class SubClass : BaseClass
    {
        internal new void TestMethod1()
        {
            Console.WriteLine("SubMethod1");
            TestMethod2();
            base.TestMethod1();
        }

        internal override void TestMethod2()
        {
            Console.WriteLine("SubMethod2");
        }
    }

        static void Main(string[] args)
        {
            SubClass sub = new SubClass ();
            sub.TestMethod1();
        }

What's the output on console?

SubMethod1

SubMethod2

BaseMethod1

SubMethod2

Example2:

    class BaseClass
    {
        internal void TestMethod1()
        {
            Console.WriteLine("BaseMethod1");
            TestMethod2();
        }

        internal virtual void TestMethod2()
        {
            Console.WriteLine("BaseMethod2");
        }
    }

    class SubClass : BaseClass
    {
        internal new void TestMethod1()
        {
            Console.WriteLine("SubMethod1");
            TestMethod2();
            base.TestMethod1();
        }

        internal override void TestMethod2()
        {
            Console.WriteLine("SubMethod2");
        }
    }

    class SubSubClass : SubClass
    {
        internal new void TestMethod1()
        {
            Console.WriteLine("SubSubMethod1");
            TestMethod2();
            base.TestMethod1();
        }

        internal override void TestMethod2()
        {
            Console.WriteLine("SubSubMethod2");
        }
    }

        static void Main(string[] args)
        {
            SubSubClass sub = new SubSubClass();
            sub.TestMethod1();
        }

What's the output on console?

SubSubMethod1

SubSubMethod2

SubMethod1

SubSubMethod2

BaseMethod1

SubSubMethod2