C#设计模式六大原则之依赖倒置原则

C#设计模式六大原则是单一职责原则、里氏替换原则、依赖倒置原则、接口隔离原则、迪米特法则、开闭原则。它们不是要我们刻板的遵守，而是根据实际需要灵活运用。只要对它们的遵守程度在一个合理的范围内，努为做到一个良好的设计。以下介绍C#依赖倒置原则。

依赖倒置原则（Dependence Inversion Principle）

依赖倒置原则（Dependence Inversion Principle）是程序要依赖于抽象接口，不要依赖于具体实现。简单的说就是要求对抽象进行编程，不要对实现进行编程，这样就降低了客户与实现模块间的耦合。高层模块不应该依赖低层模块，二者都应该依赖其抽象；抽象不应该依赖细节；细节应该依赖抽象。面向对象的开发很好的解决了这个问题，一般情况下抽象的变化概率很小，让用户程序依赖于抽象，实现的细节也依赖于抽象。即使实现细节不断变动，只要抽象不变，客户程序就不需要变化。这大大降低了客户程序与实现细节的耦合度。

例如，

1）一般的反面设计实现

using System;
namespace ConsoleApplication
{public class HondaCar{public void Run(){Console.WriteLine("本田开始启动");}public void Turn(){Console.WriteLine("本田开始转弯");}public void Stop(){Console.WriteLine("本田开始停车");}}public class FordCar{public void Run(){Console.WriteLine("福特开始启动");}public void Turn(){Console.WriteLine("福特开始转弯");}public void Stop(){Console.WriteLine("福特开始停车");}}public class BmwCar{public void Run(){Console.WriteLine("福特开始启动");}public void Turn(){Console.WriteLine("福特开始转弯");}public void Stop(){Console.WriteLine("福特开始停车");}}public class AutoSystem{public enum CarType{Ford, Honda, Bmw};HondaCar hcar = new HondaCar();FordCar fcar = new FordCar();BmwCar bcar = new BmwCar();private CarType type;public AutoSystem(CarType type){this.type = type;}public void RunCar(){if (type == CarType.Ford){fcar.Run();}else if (type == CarType.Honda){hcar.Run();}else if (type == CarType.Bmw){bcar.Run();}}public void TurnCar(){if (type == CarType.Ford){fcar.Turn();}else if (type == CarType.Honda){hcar.Turn();}else if (type == CarType.Bmw){bcar.Turn();}}public void StopCar(){if (type == CarType.Ford){fcar.Stop();}else if (type == CarType.Honda){hcar.Stop();}else if (type == CarType.Bmw){bcar.Stop();}}}class Program{public static void Main(){AutoSystem autoSystem = new AutoSystem(AutoSystem.CarType.Honda);autoSystem.RunCar();autoSystem.TurnCar();autoSystem.StopCar();Console.ReadKey();}}
}

 2）依赖倒置原则的实现

using System;
namespace ConsoleApplication
{public interface ICar{void Run();void Turn();void Stop();}public class BmwCar : ICar{public void Run(){Console.WriteLine("宝马开始启动");}public void Turn(){Console.WriteLine("宝马开始转弯");}public void Stop(){Console.WriteLine("宝马开始停车");}}public class FordCar : ICar{public void Run(){Console.WriteLine("福特开始启动");}public void Turn(){Console.WriteLine("福特开始转弯");}public void Stop(){Console.WriteLine("福特开始停车");}}public class HondaCar : ICar{public void Run(){Console.WriteLine("本田开始启动");}public void Turn(){Console.WriteLine("本田开始转弯");}public void Stop(){Console.WriteLine("本田开始停车");}}public class AutoSystem{private ICar icar;public AutoSystem(ICar icar){this.icar = icar;}public void RunCar(){icar.Run();}public void TurnCar(){icar.Turn();}public void StopCar(){icar.Stop();}}class Program{public static void Main(){AutoSystem autoSystem = new AutoSystem(new HondaCar());autoSystem.RunCar();autoSystem.TurnCar();autoSystem.StopCar();Console.ReadKey();}}
}