什么是委托？
将一个方法作为参数传递给另一个方法。
注意：委托所指向的方法必须和委托具有相同的签名（返回值类型和参数列表）
举例
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp2 {
//声明一个委托指向一个函数
public delegate void DelSayHi(string name);
class Program {
static void Main(string[] args) {
//DelSayHi del = new DelSayHi(SayHiEnglish);
//DelSayHi del = SayHiEnglish; //函数可以直接赋值给一个委托对象。前提：委托的签名必须和函数的签名一样。
//del("张三");
//将方法作为参数传给了另一个方法
Test("张三", SayHiChinese);
Console.ReadKey();
}
/// <summary>
///
/// </summary>
/// <param name="name"></param>
/// <param name="del">参数是委托类型</param>
public static void Test(string name, DelSayHi del) {
//调用
del(name);
}
public static void SayHiChinese(string name) {
Console.WriteLine("吃了么？" + name);
}
public static void SayHiEnglish(string name) {
Console.WriteLine("Nice to meet you" + name);
}
}
}
运行：
举例
现在有三个需求：
1、将一个字符串数组中每个元素都转换成大写
2、将一个字符串数组中每个元素都转换成小写
3、将一个字符串数组中每个元素两边都加上 双引号
原始版
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp2 {
class Program {
static void Main(string[] args) {
//三个需求
//1、将一个字符串数组中每个元素都转换成大写
//2、将一个字符串数组中每个元素都转换成小写
//3、将一个字符串数组中每个元素两边都加上 双引号
string[] names = { "abCDefG", "HIJKlmnOP", "QRsTuvW", "XyZ" };
//ProStToUpper(names);
//ProStrToLower(names);
ProStrSYH(names);
for (int i = 0; i < names.Length; i++) {
Console.WriteLine(names[i]);
}
Console.ReadKey();
}
public static void ProStToUpper(string[] name) {
for (int i = 0; i < name.Length; i++) {
name[i] = name[i].ToUpper();
}
}
public static void ProStrToLower(string[] name) {
for (int i = 0; i < name.Length; i++) {
name[i] = name[i].ToLower();
}
}
public static void ProStrSYH(string[] names) {
for (int i = 0; i < names.Length; i++) {
names[i] = """ + names[i] + """;
}
}
}
}
运行结果：
委托版
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp2 {
//声明一个委托指向一个函数
public delegate string DelProStr(string name);
class Program {
static void Main(string[] args) {
//三个需求
//1、将一个字符串数组中每个元素都转换成大写
//2、将一个字符串数组中每个元素都转换成小写
//3、将一个字符串数组中每个元素两边都加上 双引号
string[] names = { "abCDefG", "HIJKlmnOP", "QRsTuvW", "XyZ" };
ProStr(names, StrToUpper);
//ProStr(names, StrToLower);
//ProStr(names, StrSYH);
for (int i = 0; i < names.Length; i++) {
Console.WriteLine(names[i]);
}
Console.ReadKey();
}
public static void ProStr(string[] name, DelProStr del) {
for (int i = 0; i < name.Length; i++) {
name[i] = del(name[i]);
}
}
public static string StrToUpper(string name) {
return name.ToUpper();
}
public static string StrToLower(string name) {
return name.ToLower();
}
public static string StrSYH(string name) {
return """ + name + """;
}
}
}
运行：
匿名函数版
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp2 {
//声明一个委托指向一个函数
public delegate string DelProStr(string name);
class Program {
static void Main(string[] args) {
//三个需求
//1、将一个字符串数组中每个元素都转换成大写
//2、将一个字符串数组中每个元素都转换成小写
//3、将一个字符串数组中每个元素两边都加上 双引号
string[] names = { "abCDefG", "HIJKlmnOP", "QRsTuvW", "XyZ" };
ProStr(names, delegate (string name) {
return name.ToUpper();
});
for (int i = 0; i < names.Length; i++) {
Console.WriteLine(names[i]);
}
Console.ReadKey();
}
public static void ProStr(string[] name, DelProStr del) {
for (int i = 0; i < name.Length; i++) {
name[i] = del(name[i]);
}
}
}
}
运行：
匿名函数：当方法只执行一次时可以考虑写成匿名函数。
lamda表达式版
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp4 {
//声明一个委托指向一个函数
public delegate string DelProStr(string name);
class Program {
static void Main(string[] args) {
//三个需求
//1、将一个字符串数组中每个元素都转换成大写
//2、将一个字符串数组中每个元素都转换成小写
//3、将一个字符串数组中每个元素两边都加上 双引号
string[] names = { "abCDefG", "HIJKlmnOP", "QRsTuvW", "XyZ" };
ProStr(names, (name)=> {
return name.ToUpper();
});
for (int i = 0; i < names.Length; i++) {
Console.WriteLine(names[i]);
}
Console.ReadKey();
}
public static void ProStr(string[] name, DelProStr del) {
for (int i = 0; i < name.Length; i++) {
name[i] = del(name[i]);
}
}
}
}
运行：
泛型委托
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp2 {
//泛型委托
public delegate int DelCompare<T>(T t1, T t2);
// public delegate int DelCompare(object o1, object o2);
class Program {
static void Main(string[] args) {
int[] nums = { 1, 2, 3, 4, 5 };
int max = GetMax<int>(nums, Compare1);
Console.WriteLine(max);
string[] names = { "abcdefg", "fdsfds", "fdsfdsfdsfdsfdsfdsfdsfsd" };
string max1 = GetMax<string>(names, (string s1, string s2) => {
return s1.Length - s2.Length;
});
Console.WriteLine(max1);
Console.ReadKey();
}
/// <summary>
///
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="nums"></param>
/// <param name="del"> 泛型委托</param>
/// <returns></returns>
public static T GetMax<T>(T[] nums, DelCompare<T> del) {
T max = nums[0];
for (int i = 0; i < nums.Length; i++) {
//要传一个比较的方法
if (del(max, nums[i]) < 0) {
max = nums[i];
}
}
return max;
}
public static int Compare1(int n1, int n2) {
return n1 - n2;
}
}
}
运行：
lamda表达式
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp3 {
public delegate void DelOne();
public delegate void DelTwo(string name);
public delegate string DelThree(string name);
class Program {
static void Main(string[] args) {
//DelOne delOne = delegate () { };
DelOne delOne = () => { };
//DelTwo delTwo = delegate(string name){ };
DelTwo delTwo = (string name) => { };
//DelThree delThree = delegate(string name) { return name; };
//DelThree delThree = (string name) => { return name; };
//或者string也可以不写
DelThree delThree = (name) => { return name; };
List<int> list = new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
list.RemoveAll(n => n > 4);
foreach (var item in list) {
Console.WriteLine(item);
}
Console.ReadKey();
}
}
}
运行：
使用委托进行窗体传值
效果
实现
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApp9 {
public partial class Form1 : Form {
public Form1() {
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e) {
Form2 form2 = new Form2(ShowMsg);
form2.Show();
}
void ShowMsg(string str) {
label1.Text = str;
}
}
}
再创建Form2窗体
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApp9 {
//声明一个委托
public delegate void DelTest(string str);
public partial class Form2 : Form {
public DelTest _del;
public Form2(DelTest del) {
this._del = del;
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e) {
_del(textBox1.Text);
}
}
}
多播委托
委托布局指向一个函数，也可指向多个函数
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp4 {
public delegate void DelTest();
class Program {
static void Main(string[] args) {
DelTest del = T1;
del += T2;
del += T3;
del += T4;
del -= T3;
del -= T1;
del();
Console.ReadKey();
}
public static void T1() {
Console.WriteLine("我是T1");
}
public static void T2() {
Console.WriteLine("我是T2");
}
public static void T3() {
Console.WriteLine("我是T3");
}
public static void T4() {
Console.WriteLine("我是T4");
}
}
}
运行：
