【C#语言入门】22. 接口、依赖反转、单元测试

一、接口与单元测试

• 接口的产生：自底向上（重构），自顶向下（设计）
• C#中接口的实现（隐式，显式，多接口）
• 语言对面向对象设计的内建支持：依赖反转，接口隔离，开/闭原则……

//不使用接口，会很麻烦
class Program
{static void Main(string[] args){int[] nums1 = new int[] { 1, 2, 3, 4, 5 };ArrayList nums2 = new ArrayList() { 1, 2, 3, 4, 5};Console.WriteLine(Sum(num1));Console.WriteLine(Avg(num1));Console.WriteLine(Sum(num2));Console.WriteLine(Avg(num2));}static int Sum(int[] nums){int sum = 0;foreach (int x in nums) {sum += x;}return sum;}static double Avg(int[] nums){int sum = 0;double count = 0;foreach(int x in nums){sum += x;count++;}return sum/count;}static int Sum(ArrayList nums){int sum = 0;foreach(var x in nums){sum += (int)x;}return sum;}static double Avg(ArrayList nums){int sum = 0;double count = 0;foreach(var x in nums){sum += (int)x;count++;}return sum/count;}
}

//使用了IEnumerable接口
class Program
{static void Main(string[] args){int[] nums1 = new int[] { 1, 2, 3, 4, 5 };ArrayList nums2 = new ArrayList() { 1, 2, 3, 4, 5};Console.WriteLine(Sum(nums1));Console.WriteLine(Avg(nums1));Console.WriteLine(Sum(nums2));Console.WriteLine(Avg(nums2));}static int Sum(IEnumerable nums){int sum = 0;foreach (int x in nums) {sum += x;}return sum;}static double Avg(IEnumerable nums){int sum = 0;double count = 0;foreach(int x in nums){sum += x;count++;}return sum/count;}}

二、依赖

在现实世界中，由于自身能力有限，合作是一个非常常见的行为，而面向对象是对现实世界的抽象，因此也存在着类与类、对象与对象的合作，即”依赖“。依赖的出现伴随着耦合，依赖越直接，耦合度越高。

class Program
{static void Main(string[] args){var user = new PhoneUser(new NokiaPhone());//var user = new PhoneUser(new EricssonPhone());超级无敌松耦合，只要改这里就能实现手机切换user.UsePhone();}}class PhoneUser
{private IPhone _phone;public PhoneUser(IPhone phone){_phone = phone;}public void UsePhone(){_phone.Dail();_phone.PickUp();_phone.Send();_phone.Receive();}
}interface IPhone
{void Dail();void PickUp();void Send();void Receive();
}class NokiaPhone:IPhone
{public void Dail(){Console.WriteLine("Nokia calling...");}public void PickUp(){Console.WriteLine("Hello!This is Tom");}public void Receive(){Console.WriteLine("Nokia message ring...");}public void Send(){Console.WriteLine("Hello!");}
}class EricssonPhone : IPhone
{public void Dail(){Console.WriteLine("Ericsson calling...");}public void PickUp(){Console.WriteLine("Hello!This is Tom");}public void Receive(){Console.WriteLine("Ericsson message ring...");}public void Send(){Console.WriteLine("Hello!");}
}

注意：在代码中如果有可以替换的地方，就一定有接口的存在，接口就是为了解耦/松耦合而生，他最大的好处就是可以让功能的提供方可以方便替换，减少紧耦合时提供方可能带来的风险。

• 依赖反转原则