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:
FuncMyAdd = (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) { //1 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 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; //3 FuncMyAdd = (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 + $"两数相减结果:{MyReduce(7, 2).ToString()}" + Environment.NewLine; //4 MyCalculate = (int x, int y) => { return x + y; }; textBox1.Text = textBox1.Text+$"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; } 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:
FuncMyOperate = (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
FuncMyGetMax = (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; FuncMyGetMax = (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:
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