. NET Foundation Supplements (4) Delegate and event 1

Onedelegate Peek: An object that owns a method

(1) Essence: An object that holds one or more methods; a delegate differs from a typical object in that the execution of a delegate actually executes the method it "holds".

(2) How to use a delegate?

① declaring delegate type (delegate keyword)

② declaring a delegate variable using the delegate type

③ Adding a method to a delegate type

④ Invoke Delegate Execution method

(3) The constancy of the entrustment:

The combination delegate, the delegate = = Increment method, and the delegate-to-= Removal method Let us look like the delegates were modified, but they were not modified. In fact, the delegate is constant .

　　What actually happens when you increment and remove a method for a delegate is to create a new delegate whose invocation list is the result of the addition and removal of the method.

delegate void Printfunction (); class test{public   void Print1 ()//instance method   {      Console.WriteLine ("Print1-- Instance ");   }   public static void Print2 ()//static method   {      Console.WriteLine ("Print2-Static");}   } Class program{   static void Main ()   {      Test t = new Test ();                       Printfunction PF;                              PF = t.print1;       PF + = Test.print2;      PF + = T.print1;      PF + = Test.print2;      if (PF! = null)                               {          pf ();           }                                else       {             Console.WriteLine ("Delegate is Empty");        }   }}

Ii. Anonymous Methods

In a method held by a delegate, if a method is used only once, in which case it is not necessary to create a separate named method in addition to the need to create the delegate syntax. Anonymous methods came into being.

　　An anonymous method is a method that inline (inline) declares when the delegate is initialized.

Using System;class program{  delegate int otherdel (int inparam);  static void Main ()  {    Otherdel del = delegate (int x)                   {                     return x + +;                   };    Console.WriteLine ("{0}", Del (5));    Console.WriteLine ("{0}", Del (6));}  }

Third, lambda expression: Another form of anonymous method, easier to read

(1) Essence: "Grammatical sugar" which simplifies grammar;

(2) Key points:

The list of parameters in the ①LAMBDA expression (number of parameters, type and location) must match the delegate;

A parameter list in a ② expression does not necessarily need to contain a type unless the delegate has a ref or out keyword (the declaration must be displayed at this time);

③ if there are no arguments, a set of empty parentheses must be used;

(3) Syntax:

All lambda expressions use the lambda operator =>, and the operator reads "goes to". The left side of the lambda operator is the input parameter (if any), and the right is the expression or statement block.

Reference article:

Http://www.cnblogs.com/edisonchou/p/3704510.html

Http://www.cnblogs.com/kingmoon/archive/2011/05/03/2035696.html

. NET Foundation Supplements (4) Delegate and event 1