[你必须知道的.NET] 第六回：深入浅出关键字---base和this

using?System;namespace?Anytao.net.My_Must_net{????public?class?Action????{????????public?static?void?ToRun(Vehicle?vehicle)????????{????????????Console.WriteLine("{0}?is?running.",?vehicle.ToString());????????}????}????public?class?Vehicle????{????????private?string?name;????????private?int?speed;????????private?string[]?array?=?new?string[10];????????public?Vehicle()????????{????????}????????//限定被相似的名称隐藏的成员????????public?Vehicle(string?name,?int?speed)????????{????????????this.name?=?name;????????????this.speed?=?speed;????????}????????public?virtual??void?ShowResult()????????{????????????Console.WriteLine("The?top?speed?of?{0}?is?{1}.",?name,?speed);????????}????????public?void?Run()????????{????????????//传递当前实例参数????????????Action.ToRun(this);????????}????????//声明索引器，必须为this，这样就可以像数组一样来索引对象????????public?string??this[int?param]????????{????????????get{return?array[param];}????????????set{array[param]?=?value;}????????}????}????public?class?Car:?Vehicle????{????????//派生类和基类通信，以base实现，基类首先被调用????????//指定创建派生类实例时应调用的基类构造函数????????public?Car()????????????:?base("Car",?200)????????{?}????????public?Car(string?name,?int?speed)????????????:?this()????????{?}????????public?override?void?ShowResult()????????{????????????//调用基类上已被其他方法重写的方法????????????base.ShowResult();????????????Console.WriteLine("It's?a?car's?result.");????????}????}????public?class?Audi?:?Car????{????????public?Audi()????????????:?base("Audi",?300)????????{?}????????public?Audi(string?name,?int?speed)????????????:?this()????????{?????????}????????public?override?void?ShowResult()????????{????????????//由三层继承可以看出，base只能继承其直接基类成员????????????base.ShowResult();????????????base.Run();????????????Console.WriteLine("It's?audi's?result.");????????}????}????public?class?BaseThisTester????{????????public?static?void?Main(string[]?args)????????{????????????Audi?audi?=?new?Audi();????????????audi[1]?=?"A6";????????????audi[2]?=?"A8";????????????Console.WriteLine(audi[1]);????????????audi.Run();????????????audi.ShowResult();????????}????}}

1. 执行System.Object.Object();
2. 执行Vehicle.Vehicle(string name,int speed);
3. 执行Car.Car();
4. 执行Car.Car(string name,int speed);
5. 执行Audi.Audi();
6. 执行Audi.Audi(string name,int speed)。

• 尽量少用或者不用base和this。除了决议子类的名称冲突和在一个构造函数中调用其他的构造函数之外，base和this的使用容易引起不必要的结果。
• 在静态成员中使用base和this都是不允许的。原因是，base和this访问的都是类的实例，也就是对象，而静态成员只能由类来访问，不能由对象来访问。
• base是为了实现多态而设计的。
• 使用this或base关键字只能指定一个构造函数，也就是说不可同时将this和base作用在一个构造函数上。
• 简单的来说，base用于在派生类中访问重写的基类成员；而this用于访问本类的成员，当然也包括继承而来公有和保护成员。
• 除了base，访问基类成员的另外一种方式是：显示的类型转换来实现。只是该方法不能为静态方法。