C#入门详解(15)

接口隔离原则，反射，特性，依赖注入

接口隔离原则：服务调用者不会多要

违反接口隔离原则情况一：

情景实例：女孩开车老撞车，男朋友想给她买个坦克开，目标：这个女生既能开车也能开坦克

代码再现：

  public class Program
    {
        static void Main(string[] args)
        {
            Driver driver = new Driver(new Car());
            driver.Driving();
        }
    }

    public interface IVehicle
    {
        void Run();
    }

    public interface ITank
    {
        void Run();
        void Fire();
    }

    public class Car : IVehicle
    {
        public void Run()
        {
            Console.WriteLine("Car is running!");
        }
    }

    public class Tank : ITank
    {
        public void Fire()
        {
            Console.WriteLine("I can firing!");
        }

        public void Run()
        {
            Console.WriteLine("Tank is running!");
        }
    }

    public class Driver
    {
        private IVehicle vehicle;

        public Driver(IVehicle vehicle)
        {
            this.vehicle = vehicle;
        }

        public void Driving()
        {
            this.vehicle.Run();
        }

    }

代码可知，这个女孩只能开实现IVechel的交通工具，想让她开坦克，就得添加一个ITank 类型字段，这样做得话，会导致多要了一种功能：坦克的“开火”，简言之这个ITank接口是个胖接口，可做如下优化：

    public interface ISweep
    {
        void Fire();
    }

    public interface ITank:IVehicle,ISweep
    {
    }

这种做法注意千万注意过犹不及，功能分化成太多小接口，会导致颗粒度太小。

违反接口隔离原则情况二：

例：将上述代码中Driver中的是ITank 类型字段，从而将合格的IVechel这个小接口挡在消费之外

例：当应用foreach迭代元素：

  static void Main(string[] args)
        {
            int[] arr1 = new int[] { 1, 2, 3, 4, 5 };
            ArrayList arr2 = new ArrayList { 1, 2, 3, 4, 5 };
            var arr3 = new OnlyIEnumble(arr1);
            Console.WriteLine(Sum(arr1));
            Console.WriteLine(Sum(arr2));
            //Console.WriteLine(Sum(arr3));
        }

        public static int Sum(ICollection collection)
        {
            int result = 0;
            foreach (var item in collection)
            {
                result += (int)item;
            }
            return result;
        }

这样是没有问题的，但当我们实现自己的IEnumerable类之后，ICollection就不能满足需求了

    public class Program
    {
        static void Main(string[] args)
        {
            int[] arr1 = new int[] { 1, 2, 3, 4, 5 };
            ArrayList arr2 = new ArrayList { 1, 2, 3, 4, 5 };
            var arr3 = new OnlyIEnumble(arr1);
            Console.WriteLine(Sum(arr1));
            Console.WriteLine(Sum(arr2));
            //Console.WriteLine(Sum(arr3));
        }

        public static int Sum(ICollection collection)
        {
            int result = 0;
            foreach (var item in collection)
            {
                result += (int)item;
            }
            return result;
        }

    }

    public class OnlyIEnumble : IEnumerable
    {
        private int[] arr_;

        public OnlyIEnumble(int[] arr)
        {
            arr_ = arr;
        }

        public IEnumerator GetEnumerator()
        {
            return new MyEnum(this);
        }

        //成员类
        //迭代器
        public class MyEnum : IEnumerator
        {
            private OnlyIEnumble OnlyIEnumble;

            private int _head;

            public MyEnum(OnlyIEnumble onlyIEnumble)
            {
                OnlyIEnumble = onlyIEnumble;
                _head = -1;
            }

            public object Current
            {
                get
                {
                    return (object)OnlyIEnumble.arr_[_head];
                }
            }

            public bool MoveNext()
            {
                if (++_head<OnlyIEnumble.arr_.Length)
                {
                    return true;
                }
                return false;
            }

            public void Reset()
            {
                _head = -1;
            }
        }

    }