C#委托初探
委托是一种定义方法签名的类型，可以与具有兼容签名的任何方法关联。您可以通过委托调用其中已添加的方法列表。委托用于将方法作为参数传递给其他方法。事件处理程序就是通过委托调用的方法。您可以创建一个自定义方法，当发生特定事件时某个类（例如 Windows 控件）就可以调用您的方法。button的单击事件发生后，通过委托这个管道找到用户添加的处理方法，从而执行方法；不必像之前win32程序那样循环等待某个事件消息。
先直接添端代码进来，
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 6 namespace Test_Delegate 7 { 8 //定义一个委托，对应方法签名为 int Fun(int , int ) 9 //编译器会自动生成一个委托类 dgOP,在此相当于声明一个类对象，稍后使用时new实例化 10 //继承链如：Delegate:MulticastDelegate:Delegate:ICloneable,ISerializable 11 public delegate int dgOP(int x, int y); 12 //生成的类形如 13 //sealed class dgOP : System.MulticastDelegate 14 //{ 15 // //构造函数，原理不清楚 ！！ 16 // public dgOP(object target,unit functionAddr); 17 // //成员函数，可在外调用 18 // public virtual int Invoke(int x, int y); 19 // public virtual IAsyncResult BeginInvoke(int x, int y 20 // , AsyncCallback callback, object @object); 21 // public virtual int EndInvoke(IAsyncResult result); 22 //} 23 24 public class SimpleMath 25 { 26 /***********静态方法*******************/ 27 public static int Add(int x, int y) 28 { 29 Console.WriteLine("add"); 30 return x + y; 31 } 32 public static int Square(int x) 33 { 34 return x * x; 35 } 36 /***********动态方法*******************/ 37 38 public int Sub(int x, int y) 39 { 40 Console.WriteLine("sub"); 41 return x - y; 42 } 43 } 44 45 class Program 46 { 47 static dgOP dg; 48 static void Main(string[] args) 49 { 50 //静态方法 51 //实例化上文中定义的（编译器自动生成的）委托类，并指定方法 52 //+=内部隐式调用dgOP.Combine 53 //Del(new dgOP(SimpleMath.Add)); 54 dg = dgOP.Combine(new dgOP(SimpleMath.Add),new dgOP(new SimpleMath().Sub)) as dgOP; 55 //执行调用列表的函数,但最终只返回最后一个函数调用返回值。 56 //dg(10 , 20)内部隐式调用 dg.Invoke(20 , 10) 57 Tools.OutputParams(dg(10 , 20)); 58 Tools.OutputParams(dg.Invoke(20, 10)); 59 //DisplayDelegate(dg); 60 Tools.NewLine(); 61 62 ////动态方法 63 //SimpleMath m=new SimpleMath(); 64 //dgOP dg2 = new dgOP(m.Sub); 65 //Tools.OutputParams(dg2(10,20),dg2.Invoke(20,10)); 66 //DisplayDelegate(dg2); 67 ////委托已经声明为方法签名为：void Fun(int x,int y)，对应2个参数 68 ////SimpleMath.Square只含一个参数 69 ////dgOP dg3 = new dgOP(SimpleMath.Square); 70 71 Tools.Pause(); 72 } 73 74 private static void Del(dgOP dgOP) 75 { 76 dg += dgOP; 77 } 78 79 80 81 private static dgOP Del() 82 { 83 dgOP dg = new dgOP(SimpleMath.Add); 84 dg += new dgOP(new SimpleMath().Sub); 85 return dg; 86 } 87 88 private static void DisplayDelegate(dgOP dg) 89 { 90 //输出委托列表内部的方法签名，类对象 91 foreach (Delegate item in dg.GetInvocationList()) 92 { 93 Tools.OutputParams(item.Method, item.Target); 94 } 95 } 96 97 98 } 99 }
Tools类只是个工具，用来输出值至控制台，或者另起一行，停止控制台。
委托是最底层，事件是较上层，用来简化处理委托声明，封装维护调用列表。
1 #region Using directives 2 3 using System; 4 using System.Collections.Generic; 5 using System.Text; 6 7 #endregion 8 9 namespace CarEvents 10 { 11 class Program 12 { 13 static void Main(string[] args) 14 { 15 Console.WriteLine("***** Fun with Events *****\n"); 16 17 // Make a car as usual. 18 Car c1 = new Car("SlugBug", 100, 10); 19 20 // Register event handlers. 21 c1.AboutToBlow += new Car.CarEventHandler(c1_AboutToBlow); 22 c1.AboutToBlow += new Car.CarEventHandler(CarIsAlmostDoomed); 23 c1.AboutToBlow += new Car.CarEventHandler(CarAboutToBlow); 24 25 Car.CarEventHandler d = new Car.CarEventHandler(CarExploded); 26 c1.Exploded += d; 27 28 // Speed up (this will generate the events.) 29 Console.WriteLine("***** Speeding up *****"); 30 for (int i = 0; i < 6; i++) 31 c1.Accelerate(20); 32 33 // Remove CarExploded method 34 // from invocation list. 35 c1.Exploded -= d; 36 37 Console.WriteLine("\n***** Speeding up *****"); 38 for (int i = 0; i < 6; i++) 39 c1.Accelerate(20); 40 41 Console.ReadLine(); 42 } 43 44 static void c1_AboutToBlow(string msg) 45 { 46 Console.WriteLine("xxxx"); 47 } 48 49 public static void CarAboutToBlow(string msg) 50 { Console.WriteLine(msg); } 51 52 public static void CarIsAlmostDoomed(string msg) 53 { Console.WriteLine("Critical Message from Car: {0}", msg); } 54 55 public static void CarExploded(string msg) 56 { Console.WriteLine(msg); } 57 58 } 59 } 60 61 #region Using directives 62 63 using System; 64 using System.Collections.Generic; 65 using System.Text; 66 67 #endregion 68 69 namespace CarEvents 70 { 71 public class Car 72 { 73 //// This delegate works in conjunction with the 74 //// Car’s events. 75 //public delegate void CarEventHandler(string msg); 76 77 //// This car can send these events. 78 //public event CarEventHandler Exploded; 79 //public event CarEventHandler AboutToBlow; 80 81 public delegate void CarEventHandler(string msg); 82 83 public event CarEventHandler Exploded; 84 public event CarEventHandler AboutToBlow; 85 #region Basic Car members... 86 87 #region Nested radio 88 // Radio as nested type 89 public class Radio 90 { 91 public void TurnOn(bool on) 92 { 93 if (on) 94 Console.WriteLine("Jamming..."); 95 else 96 Console.WriteLine("Quiet time..."); 97 } 98 } 99 #endregion 100 101 // Internal state data. 102 private int currSpeed; 103 private int maxSpeed; 104 private string petName; 105 106 // Is the car alive or dead? 107 bool carIsDead; 108 109 // A car has-a radio. 110 private Radio theMusicBox = new Radio(); 111 112 public Car() 113 { 114 maxSpeed = 100; 115 } 116 117 public Car(string name, int max, int curr) 118 { 119 currSpeed = curr; 120 maxSpeed = max; 121 petName = name; 122 } 123 124 public void CrankTunes(bool state) 125 { 126 theMusicBox.TurnOn(state); 127 } 128 #endregion 129 130 #region Accelerate method 131 public void Accelerate(int delta) 132 { 133 // If the car is dead, fire Exploded event. 134 if (carIsDead) 135 { 136 if (Exploded != null) 137 Exploded("Sorry, this car is dead..."); 138 } 139 else 140 { 141 currSpeed += delta; 142 143 // Almost dead? 144 if (10 == maxSpeed - currSpeed 145 && AboutToBlow != null) 146 { 147 AboutToBlow("Careful buddy! Gonna blow!"); 148 } 149 150 // Still OK! 151 if (currSpeed >= maxSpeed) 152 carIsDead = true; 153 else 154 Console.WriteLine("->CurrSpeed = {0}", currSpeed); 155 } 156 } 157 #endregion 158 159 } 160 }
匿名方法是简化了委托及方法定义，不必再手动定义方法，直接间写在委托中。
1 #region Using directives 2 3 using System; 4 using System.Collections.Generic; 5 using System.Text; 6 7 #endregion 8 9 namespace AnonymousMethods 10 { 11 class Program 12 { 13 static void Main(string[] args) 14 { 15 Console.WriteLine("***** Anonymous Methods *****"); 16 17 int aboutToBlowCounter = 0; 18 19 // Make a car as usual. 20 Car c1 = new Car("SlugBug", 100, 10); 21 22 // Register event handlers as anonymous methods. 23 c1.AboutToBlow += delegate 24 { 25 aboutToBlowCounter++; 26 Console.WriteLine("Eek! Going too fast!"); 27 }; 28 29 c1.AboutToBlow += delegate(object sender, CarEventArgs e) 30 { 31 aboutToBlowCounter++; 32 Console.WriteLine("Message from Car: {0}", e.msg); 33 }; 34 35 c1.Exploded += delegate(object sender, CarEventArgs e) 36 { Console.WriteLine("Message from Car: {0}", e.msg); }; 37 38 // Speed up (this will generate the events.) 39 Console.WriteLine("\n***** Speeding up *****"); 40 for (int i = 0; i < 6; i++) 41 c1.SpeedUp(20); 42 43 Console.WriteLine("AboutToBlow event was fired {0} times", 44 aboutToBlowCounter); 45 46 Console.ReadLine(); 47 } 48 } 49 } 50 #region Using directives 51 52 using System; 53 using System.Collections.Generic; 54 using System.Text; 55 56 #endregion 57 58 namespace AnonymousMethods 59 { 60 //与上面的事件代码类似 61 public class CarEventArgs : EventArgs 62 { 63 public readonly string msg; 64 public CarEventArgs(string message) 65 { 66 msg = message; 67 } 68 } 69 70 public class Car 71 { 72 // This delegate works in conjunction with the 73 // Car’s events. 74 public delegate void CarEventHandler(object sender, CarEventArgs e); 75 76 // This car can send these events. 77 public event CarEventHandler Exploded; 78 public event CarEventHandler AboutToBlow; 79 80 #region Basic Car members... 81 #region Nested radio 82 // Radio as nested type 83 public class Radio 84 { 85 public void TurnOn(bool on) 86 { 87 if (on) 88 Console.WriteLine("Jamming..."); 89 else 90 Console.WriteLine("Quiet time..."); 91 } 92 } 93 #endregion 94 95 // Internal state data. 96 private int currSpeed; 97 private int maxSpeed; 98 private string petName; 99 100 // Is the car alive or dead? 101 bool carIsDead; 102 103 // A car has-a radio. 104 private Radio theMusicBox = new Radio(); 105 106 public Car() 107 { 108 maxSpeed = 100; 109 } 110 111 public Car(string name, int max, int curr) 112 { 113 currSpeed = curr; 114 maxSpeed = max; 115 petName = name; 116 } 117 118 public void CrankTunes(bool state) 119 { 120 theMusicBox.TurnOn(state); 121 } 122 #endregion 123 124 public void SpeedUp(int delta) 125 { 126 // If the car is dead, fire Exploded event. 127 if (carIsDead && Exploded != null) 128 { 129 Exploded(this, new CarEventArgs("Sorry, this car is dead...")); 130 } 131 else 132 { 133 currSpeed += delta; 134 135 // Almost dead? 136 if (10 == maxSpeed - currSpeed 137 && AboutToBlow != null) 138 { 139 AboutToBlow(this, new CarEventArgs("Careful buddy! Gonna blow!")); 140 } 141 142 // Still OK! 143 if (currSpeed >= maxSpeed) 144 carIsDead = true; 145 else 146 Console.WriteLine("->CurrSpeed = {0}", currSpeed); 147 } 148 } 149 } 150 }
而lambdar表达式则是对匿名方法的再次简化，由此可以引申出linq,ef的语法。
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 6 namespace SimpleLambdaExpressions 7 { 8 class Program 9 { 10 static void Main(string[] args) 11 { 12 Console.WriteLine("***** Fun with Lambdas *****\n"); 13 TraditionalDelegateSyntax(); 14 AnonymousMethodSyntax(); 15 16 Console.WriteLine(); 17 LambdaExpressionSyntax(); 18 19 Console.ReadLine(); 20 } 21 22 #region Traditional delegate syntax 23 static void TraditionalDelegateSyntax() 24 { 25 // Make a list of integers. 26 List<int> list = new List<int>(); 27 list.AddRange(new int[] { 20, 1, 4, 8, 9, 44 }); 28 29 // Call FindAll() using traditional delegate syntax. 30 Predicate<int> callback = new Predicate<int>(IsEvenNumber); 31 List<int> evenNumbers = list.FindAll(callback); 32 33 Console.WriteLine("Here are your even numbers:"); 34 foreach (int evenNumber in evenNumbers) 35 { 36 Console.Write("{0}\t", evenNumber); 37 } 38 Console.WriteLine(); 39 } 40 // Target for the Predicate<> delegate. 41 static bool IsEvenNumber(int i) 42 { 43 // Is it an even number? 44 return (i % 2) == 0; 45 } 46 #endregion 47 48 #region Anonymous method syntax 49 static void AnonymousMethodSyntax() 50 { 51 // Make a list of integers using C# 3.0 52 // collection initialization syntax. 53 List<int> list = new List<int>(); 54 list.AddRange(new int[] { 20, 1, 4, 8, 9, 44 }); 55 56 List<int> evenNumbers = list.FindAll( 57 delegate(int i) 58 { 59 return (i % 2) == 0; 60 } 61 ); 62 63 Console.WriteLine("Here are your even numbers:"); 64 foreach (int evenNumber in evenNumbers) 65 { 66 Console.Write("{0}\t", evenNumber); 67 } 68 Console.WriteLine(); 69 } 70 #endregion 71 72 #region Lambda expression syntax 73 static void LambdaExpressionSyntax() 74 { 75 // Make a list of integers. 76 List<int> list = new List<int>(); 77 list.AddRange(new int[] { 20, 1, 4, 8, 9, 44 }); 78 79 // Now process each argument within a group of 80 // code statements. 81 List<int> evenNumbers = list.FindAll((i) => 82 { 83 Console.WriteLine("value of i is currently: {0}", i); 84 bool isEven = ((i % 2) == 0); 85 return isEven; 86 }); 87 88 Console.WriteLine("Here are your even numbers:"); 89 foreach (int evenNumber in evenNumbers) 90 { 91 Console.Write("{0}\t", evenNumber); 92 } 93 Console.WriteLine(); 94 } 95 #endregion 96 } 97 }
总结性的比较少，代码比较多。因为我还没有完全领悟，只是初步了解了下。
具体大家可以发挥google的优势。
