步步为营-25-委托(比大小)

1.1 找出int数组中的最大值,我们可能会这样写

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] ins = {1,2,33,44,3421,1,5,2,9,6 };
            int max = GetMax(ins);
            Console.WriteLine(max);
            Console.Read();
        }

        private static int GetMax(int[] ins)
        {
            int max = ins[0];
            foreach (int item in ins)
            {
                if (max < item)
                {
                    max = item;
                }
            }
            return max;
        }
    }
}

1.2 如果要找出string数组的最大长度呢?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] ins = {1,2,33,44,3421,1,5,2,9,6 };
            string[] strs = { "asdf",";ljsdfasldj","uasjaldf","s","asdfasdf"};
            int max = GetMax(ins);
            string maxStr = GetMax(strs);
            Console.WriteLine(max);
            Console.WriteLine(maxStr);
            Console.Read();
        }

        private static int GetMax(int[] ins)
        {
            int max = ins[0];
            foreach (int item in ins)
            {
                if (max < item)
                {
                    max = item;
                }
            }
            return max;
        }

        private static string GetMax(string[] strs)
        {
            int max = strs[0].Length;
            string str = strs[0];
            foreach (string item in strs)
            {
                if (max < item.Length)
                {
                    max = item.Length;
                    str = item;
                }
            }
            return str;
        }
    }
}

1.3 我们可以把它们以委托的方式写出来
通过分析可以发现,两种比较方法在调用具体比较时所用的方法是不同,而且如果要统一写的化应该用object[]代替

1.3.1 声明委托,用于比较两个对象,返回值是int ,例如传入两个string,通过内部比较返回是否>0,以区别两个,字符串类型的长度.

 public delegate int delCompare(object o1,object o2);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
    public delegate int delCompare(object o1,object o2);
    class Program
    {
        static void Main(string[] args)
        {
            object[] ins = {1,2,33,44,3421,1,5,2,9,6 };
            object[] strs = { "asdf",";ljsdfasldj","uasjaldf","s","asdfasdf"};
            //比较整形数组
            delCompare del = new delCompare(IntCompare);
            object max = GetMax(ins, del);

            //比较字符串           
            object maxStr = GetMax(strs, StringCompare);

            Console.WriteLine(max);
            Console.WriteLine(maxStr);
            Console.Read();
        }

     

        private static object GetMax(object[] objs,delCompare delc)
        {
            object max = objs[0];

            foreach (object item in objs)
            {
                if (delc(max,item) < 0)
                {
                    max = item;
                }
            }
            return max;
        }

        private static int IntCompare(object o1,object o2) 
        {
            return (int)o1 - (int)o2;
        }

        private static int StringCompare(object o1, object o2)
        {
            return o1.ToString().Length - o2.ToString().Length;
        }
    }
}

1.4 进一步升级

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
    public delegate int delCompare(object o1,object o2);
    class Program
    {
        static void Main(string[] args)
        {
            object[] ins = {1,2,33,44,3421,1,5,2,9,6 };
            object[] strs = { "asdf",";ljsdfasldj","uasjaldf","s","asdfasdf"};
            //比较整形数组
           // delCompare del = new delCompare(IntCompare); //1.0 通过定义委托调用方法
            //object max = GetMax(ins, del);
            object max = GetMax(ins, (o1, o2) => { return (int)o1 - (int)o2; });

            //比较字符串           
           // object maxStr = GetMax(strs, StringCompare); //2.0 直接调用方法
          //  object maxStr = GetMax(strs, delegate(object o1, object o2) { return o1.ToString().Length - o2.ToString().Length; });//3.0 通过匿名方法
            object maxStr = GetMax(strs, (o1, o2) => { return o1.ToString().Length - o2.ToString().Length; }); //4.0 lmadba表达式
            Console.WriteLine(max);
            Console.WriteLine(maxStr);
            Console.Read();
        }

     

        private static object GetMax(object[] objs,delCompare delc)
        {
            object max = objs[0];

            foreach (object item in objs)
            {
                if (delc(max,item) < 0)
                {
                    max = item;
                }
            }
            return max;
        }


      
    }
}

1.5 那么现在如果加一个Person类呢?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
   public  class Person
    {
        public String  Name { get; set; }
        public int Age { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
    public delegate int delCompare(object o1,object o2);
    class Program
    {
        static void Main(string[] args)
        {
            object[] ins = {1,2,33,44,3421,1,5,2,9,6 };
            object[] strs = { "asdf",";ljsdfasldj","uasjaldf","s","asdfasdf"};
            Person[] perons = { new Person { Name = "张三", Age = 40 }, new Person { Name = "李四", Age = 50 }, new Person { Name = "王五", Age = 80 } };

            //比较整形数组
           // delCompare del = new delCompare(IntCompare); //1.0 通过定义委托调用方法
            //object max = GetMax(ins, del);
            object max = GetMax(ins, (o1, o2) => { return (int)o1 - (int)o2; });

            //比较字符串           
           // object maxStr = GetMax(strs, StringCompare); //2.0 直接调用方法
          //  object maxStr = GetMax(strs, delegate(object o1, object o2) { return o1.ToString().Length - o2.ToString().Length; });//3.0 通过匿名方法
            object maxStr = GetMax(strs, (o1, o2) => { return o1.ToString().Length - o2.ToString().Length; }); //4.0 lmadba表达式

            //比较Person
            object maxPeople = GetMax(perons,(o1,o2) =>{ Person p1 = (Person)o1 ;Person p2 = (Person)o2 ;return p1.Age - p2.Age;});
            Person pMax = (Person)maxPeople;
            Console.WriteLine(max);
            Console.WriteLine(maxStr);
            Console.WriteLine(pMax.Name);
            Console.Read();
        }

     

        private static object GetMax(object[] objs,delCompare delc)
        {
            object max = objs[0];

            foreach (object item in objs)
            {
                if (delc(max,item) < 0)
                {
                    max = item;
                }
            }
            return max;
        }


      
    }
}

 1.6 继续观察发现

 object max = GetMax(ins, (o1, o2) => { return (int)o1 - (int)o2; });

 object maxStr = GetMax(strs, (o1, o2) => { return o1.ToString().Length - o2.ToString().Length; }); //4.0 lmadba表达式

 object maxPeople = GetMax(perons,(o1,o2) =>{ Person p1 = (Person)o1 ;Person p2 = (Person)o2 ;return p1.Age - p2.Age;});

这其中都有类型转换,装箱拆箱比较麻烦

1.7 泛型委托

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate_GetMax
{
    public delegate int delCompare<T>(T o1,T o2);
    class Program
    {
        static void Main(string[] args)
        {
            int[] ins = {1,2,33,44,3421,1,5,2,9,6 };
            string[] strs = { "asdf",";ljsdfasldj","uasjaldf","s","asdfasdf"};
            Person[] perons = { new Person { Name = "张三", Age = 40 }, new Person { Name = "李四", Age = 50 }, new Person { Name = "王五", Age = 80 } };

            //比较整形数组
           // delCompare del = new delCompare(IntCompare); //1.0 通过定义委托调用方法
            //object max = GetMax(ins, del);
            int max = GetMax(ins, (o1, o2) => { return o1 - o2; });

            //比较字符串           
           // object maxStr = GetMax(strs, StringCompare); //2.0 直接调用方法
          //  object maxStr = GetMax(strs, delegate(object o1, object o2) { return o1.ToString().Length - o2.ToString().Length; });//3.0 通过匿名方法
            string maxStr = GetMax(strs, (o1, o2) => { return o1.Length - o2.Length; }); //4.0 lmadba表达式

            //比较Person
            object maxPeople = GetMax(perons,(o1,o2) =>{return o1.Age - o2.Age;});
            Person pMax = (Person)maxPeople;
            Console.WriteLine(max);
            Console.WriteLine(maxStr);
            Console.WriteLine(pMax.Name);
            Console.Read();
        }

     

        private static T GetMax<T>(T[] objs,delCompare<T> delc)
        {
            T max = objs[0];

            foreach (T item in objs)
            {
                if (delc(max,item) < 0)
                {
                    max = item;
                }
            }
            return max;
        }


      
    }
}