Using a lambda expression，we can make the code more compact and elegant。
　　在使用lambda表达式时，可以使代码更加简洁和优雅。

　　Lambda，希腊字母λ，在C#编程语言中，被引入为Lambda表达式，表示为匿名函数（匿名方法）。
　　编程时离不开函数，函数都有函数名和函数体，声明函数名是为了方便多次使用，可是很多时候函数只使用一次，那么函数名就变得多余，这样就产生了匿名函数（匿名方法）。

　　很多编程语言都有Lambde表达式，如Python、JavaScript、Java等等，这似乎是现代编程语言的标配了。
　　作为编程语言C#和编程环境Visual Stuidio的发展，总得不停地变幻出新花样，功能还是那个功能或者略有增强，得益于编译器的强大，C#3.0推出了Lambda表达式。
　　其实这些是非必要的，只是为C#编码增加一些色彩和亮点而已，但是别人总喜欢这么写，我们就得熟悉这些规则了。

　　举例1：计算两个整数的相加和相减。

　　①  一般写法

        //声明变量private delegate int calculate(int x, int y);//声明一个用于计算的委托类型private calculate MyCalculate;//声明一个委托实例//声明函数private int Add(int x, int y){return x+y;}private int Reduce(int x, int y){return x - y;}

　　就可以直接使用了。

            MyCalculate = new calculate(Add);string StrResultAdd = MyCalculate(7, 2).ToString();MyCalculate = new calculate(Reduce);string StrResultReduce = MyCalculate(7, 2).ToString();//textBox1.Text = $"两数相加结果：{StrResultAdd}" + Environment.NewLine;textBox1.Text = textBox1.Text+ $"两数相减结果：{StrResultReduce}" + Environment.NewLine;

　　② 使用自定义的委托

　　使用自定义的委托来使用Lamda可以让代码更简洁：

            MyCalculate = delegate(int x,int y){return x + y;};textBox1.Text = textBox1.Text+"两数相加结果：" + MyCalculate(7, 2).ToString()+Environment.NewLine;MyCalculate = delegate (int x, int y){return x - y;};textBox1.Text = textBox1.Text + "两数相减结果：" + MyCalculate(7, 2).ToString() + Environment.NewLine;

　　上面得到的结果是一样的。

　　③ 使用Func委托

　　FUNC委托的重载：
　　Func;
　　Func;
　　Func;
　　使用系统内置的FUNC命名的委托来写LambDa表达式：

Func MyAdd = (int x, int y) => { return x + y; };
Func MyReduce = (int x, int y) => { return x - y; };textBox1.Text = textBox1.Text + $"两数相加结果：{MyAdd(7,2).ToString()}" + Environment.NewLine;
textBox1.Text = textBox1.Text + $"两数相减结果：{MyReduce(7, 2).ToString()}" + Environment.NewLine;

　　④ 使用规范的Lambda表达式

　　更简洁的写法：

MyCalculate = (int x, int y) => { return x + y; };
textBox1.Text = textBox1.Text+$"两数相加结果：{MyCalculate(7, 2).ToString()}" + Environment.NewLine;
MyCalculate = (int x, int y) => { return x - y; };
textBox1.Text = textBox1.Text+$"两数相减结果：{MyCalculate(7, 2).ToString()}" + Environment.NewLine;

　　完整代码：

namespace Lambda
{public partial class Form1 : Form{private delegate int calculate(int x, int y);//声明一个用于计算的委托类型private calculate MyCalculate;//声明一个委托实例public Form1(){InitializeComponent();}private void button1_Click(object sender, EventArgs e){//1MyCalculate = new calculate(Add);string StrResultAdd = MyCalculate(7, 2).ToString();MyCalculate = new calculate(Reduce);string StrResultReduce = MyCalculate(7, 2).ToString();textBox1.Text = $"两数相加结果：{StrResultAdd}" + Environment.NewLine;textBox1.Text = textBox1.Text+ $"两数相减结果：{StrResultReduce}" + Environment.NewLine;//2MyCalculate = delegate(int x,int y){return x + y;};textBox1.Text = textBox1.Text+"两数相加结果：" + MyCalculate(7, 2).ToString()+Environment.NewLine;MyCalculate = delegate (int x, int y){return x - y;};textBox1.Text = textBox1.Text + "两数相减结果：" + MyCalculate(7, 2).ToString() + Environment.NewLine;//3Func MyAdd = (int x, int y) => { return x + y; };Func MyReduce = (int x, int y) => { return x - y; };textBox1.Text = textBox1.Text + $"两数相加结果：{MyAdd(7,2).ToString()}" + Environment.NewLine;textBox1.Text = textBox1.Text + $"两数相减结果：{MyReduce(7, 2).ToString()}" + Environment.NewLine;//4MyCalculate = (int x, int y) => { return x + y; };textBox1.Text = textBox1.Text+$"两数相加结果：{MyCalculate(7, 2).ToString()}" + Environment.NewLine;MyCalculate = (int x, int y) => { return x - y; };textBox1.Text = textBox1.Text+$"两数相减结果：{MyCalculate(7, 2).ToString()}" + Environment.NewLine;}private int Add(int x, int y){return x+y;}private int Reduce(int x, int y){return x - y;}

　　结果显示：

　　上面通过对比说明了Lambda表达式的应用，可以看出这样的写法相比传统的写法还是干净利落，的确简洁而优雅一些。 　　

　　上面的可以改写：

        private delegate int calculate1(int x, int y,string str);//声明一个用于计算的委托类型private calculate1 MyCalculate1;//声明一个委托实例MyCalculate1 = (int x, int y,string StrOP) => {switch (StrOP){case "+":return x + y; break;case "-": return x - y; break;default: return 0; break;}};textBox1.Text = textBox1.Text + $"两数相加结果：{MyCalculate1(7, 2,"+").ToString()}" + Environment.NewLine;textBox1.Text = textBox1.Text + $"两数相减结果：{MyCalculate1(7, 2,"-").ToString()}" + Environment.NewLine;

　　或者：

            Func MyOperate = (int x, int y, string StrOP) => {switch (StrOP){case "+":return x + y; break;case "-": return x - y; break;default: return 0;break;}};textBox1.Text = textBox1.Text + $"两数相加结果：{MyOperate(7, 2,"+").ToString()}" + Environment.NewLine;textBox1.Text = textBox1.Text + $"两数相减结果：{MyOperate(7, 2,"-").ToString()}" + Environment.NewLine;

　　从上面的代码演示中可以看出，Lambda与委托是紧密相连的。

　　举例2：求几个数的最大值与最小值。

　　① 一般写法：

        private void button2_Click(object sender, EventArgs e){textBox1.Text += "最大值："+GetMax(new int[6]{7, 11,23,4,15,6}).ToString();textBox1.Text += Environment.NewLine;textBox1.Text += "最小值：" + GetMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();}private static int GetMax(int[] Arr){int ReturnValue = Arr[0];foreach( int a in Arr){if(a > ReturnValue) ReturnValue = a;}return ReturnValue;}private static int GetMin(int[] Arr){int ReturnValue = Arr[0];foreach (int a in Arr){if (a < ReturnValue) ReturnValue = a;}return ReturnValue;}

　　② 使用委托来改写：

        //声明委托private delegate int GetMaxOrMin(int[] Arr);private GetMaxOrMin MyGetMaxOrMin;//定义函数private static int GetMax(int[] Arr){int ReturnValue = Arr[0];foreach( int a in Arr){if(a > ReturnValue) ReturnValue = a;}return ReturnValue;}private static int GetMin(int[] Arr){int ReturnValue = Arr[0];foreach (int a in Arr){if (a < ReturnValue) ReturnValue = a;}return ReturnValue;}//使用private void button2_Click(object sender, EventArgs e){MyGetMaxOrMin = new GetMaxOrMin( GetMax);textBox1.Text += "最大值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();textBox1.Text += Environment.NewLine;MyGetMaxOrMin = new GetMaxOrMin(GetMin);textBox1.Text += "最小值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();}

　　③ 使用自定义的委托

            MyGetMaxOrMin=delegate(int[] Arr){int ReturnValue = Arr[0];foreach (int a in Arr){if (a > ReturnValue) ReturnValue = a;}return ReturnValue;};textBox1.Text += "最大值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();MyGetMaxOrMin = delegate (int[] Arr){int ReturnValue = Arr[0];foreach (int a in Arr){if (a < ReturnValue) ReturnValue = a;}return ReturnValue;};textBox1.Text += "最小值：" + GetMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();

　　到这里，我们看到这两个方法只是判断位置的代码略有不同，其他的都相同，那么这个地方就可以使用委托来代替，就是把判断方法当做参数传进去。

        private delegate Boolean Judge(int x,int y);//定义判断private Judge MyJudge;//实例化委托private delegate int GetMaxOrMin(int[] Arr,Judge j);//定义得到最大值或者最小值的计算方法private GetMaxOrMin MyGetMaxOrMin;//实例化private void button2_Click(object sender, EventArgs e){            MyGetMaxOrMin=delegate(int[] Arr,Judge MyJude){int ReturnValue = Arr[0];foreach (int a in Arr){if (MyJudge(a,ReturnValue)) ReturnValue = a;}return ReturnValue;};MyJudge = delegate (int x, int y) { return x > y; };textBox1.Text += "最大值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 },MyJudge).ToString();MyJudge = delegate (int x, int y) { return x < y; };textBox1.Text += "最小值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 },MyJudge).ToString();}

　　上面的写法的效果是一样的。

　　④ 使用Func委托

            Func MyGetMax = (int[] Arr,Judge MyJudge) => {int ReturnValue = Arr[0];foreach (int a in Arr){if (MyJudge(a, ReturnValue)) ReturnValue = a;}return ReturnValue;};MyJudge = delegate (int x, int y) { return x > y; };textBox1.Text += "最大值：" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 },MyJudge).ToString();MyJudge = delegate (int x, int y) { return x < y; };textBox1.Text += "最小值：" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();

　　⑤ 使用更简洁的Lambda表达式

            var MyGetMaxOrMin1 = (int[] Arr,Judge J1 ) =>{int ReturnValue = Arr[0];foreach (int a in Arr){if (J1(a, ReturnValue)) ReturnValue = a;}return ReturnValue;};Judge JudgeMax = (int x, int y) => { return x > y; };textBox1.Text += "最大值：" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMax).ToString();Judge JudgeMin = (int x, int y) => { return x < y; };textBox1.Text += "最小值：" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMin).ToString();

　　完整代码：

using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Security.Cryptography.X509Certificates;namespace Lambda
{public partial class Form1 : Form{private delegate int calculate(int x, int y);//声明一个用于计算的委托类型private calculate MyCalculate;//声明一个委托实例private delegate int calculate1(int x, int y,string str);//声明一个用于计算的委托类型private calculate1 MyCalculate1;//声明一个委托实例private delegate Boolean Judge(int x,int y);private Judge MyJudge;private delegate int GetMaxOrMinA(int[] Arr);private GetMaxOrMinA MyGetMaxOrMinA;private delegate int GetMaxOrMin(int[] Arr,Judge j);private GetMaxOrMin MyGetMaxOrMin;public Form1(){InitializeComponent();}private void button2_Click(object sender, EventArgs e){textBox1.Text += "最大值：" + GetMax(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();textBox1.Text += "最小值：" + GetMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();textBox1.Text += Environment.NewLine +"=====" + Environment.NewLine;MyGetMaxOrMinA = new GetMaxOrMinA(GetMax);textBox1.Text += "最大值：" + MyGetMaxOrMinA(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();MyGetMaxOrMinA = new GetMaxOrMinA(GetMin);textBox1.Text += "最小值：" + MyGetMaxOrMinA(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();textBox1.Text += Environment.NewLine + "=====" + Environment.NewLine;MyGetMaxOrMin = delegate (int[] Arr, Judge MyJude){int ReturnValue = Arr[0];foreach (int a in Arr){if (MyJudge(a, ReturnValue)) ReturnValue = a;}return ReturnValue;};MyJudge = delegate (int x, int y) { return x > y; };textBox1.Text += "最大值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();MyJudge = delegate (int x, int y) { return x < y; };textBox1.Text += "最小值：" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();textBox1.Text += Environment.NewLine +"=====" + Environment.NewLine;Func MyGetMax = (int[] Arr, Judge MyJudge) =>{int ReturnValue = Arr[0];foreach (int a in Arr){if (MyJudge(a, ReturnValue)) ReturnValue = a;}return ReturnValue;};MyJudge = delegate (int x, int y) { return x > y; };textBox1.Text += "最大值：" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();MyJudge = delegate (int x, int y) { return x < y; };textBox1.Text += "最小值：" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();textBox1.Text += Environment.NewLine +"=====" + Environment.NewLine;var MyGetMaxOrMin1 = (int[] Arr,Judge Judge1 ) =>{int ReturnValue = Arr[0];foreach (int a in Arr){if (Judge1(a, ReturnValue)) ReturnValue = a;}return ReturnValue;};Judge JudgeMax = (int x, int y) => { return x > y; };textBox1.Text += "最大值：" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMax).ToString();Judge JudgeMin = (int x, int y) => { return x < y; };textBox1.Text += "最小值：" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMin).ToString();}private static int GetMax(int[] Arr){int ReturnValue = Arr[0];foreach( int a in Arr){if(a > ReturnValue) ReturnValue = a;}return ReturnValue;}private static int GetMin(int[] Arr){int ReturnValue = Arr[0];foreach (int a in Arr){if (a < ReturnValue) ReturnValue = a;}return ReturnValue;}private static List GetEven(List list){List ReturnList =new List();foreach (var a in list){if (a %2 == 0) ReturnList.Add(a);}return ReturnList;}private static List GetOdd(List list){List ReturnList = new List();foreach (var a in list){if ( (a+1) % 2 == 0) ReturnList.Add(a);}return ReturnList;}}
}

　　显示结果图：