Delegated Learning (2)

1.1 delegated chain

Delegation is a multi-channel broadcast. Therefore, two or more non-delegated instances can be combined to form a delegation chain. The so-called delegated chain is the delegated method connected together in the form of a linked list.

The binary ++ and ++ = operators are used to combine the delegation in C #, and the-or-= Operator is used to remove a delegation from the delegation chain.

A new delegate is generated when you combine or remove a delegate instance from a delegate chain. The delegate has its own call list. The call list of the combined or removed delegate remains unchanged,

If the list of a delegated instance contains multiple methods, the method will be executed in the order of the call list when such a delegated instance is called. If a parameter contains a reference or output parameter (ref or out parameter ),

A reference to the same variable is used. Therefore, if you call a method in the list to modify the variable, the modified variable is used as the parameter for all delegate methods. If a delegate call contains a reference or output parameter or

A return value is determined by the last method in the call list.

Let's look at a simple example of a delegated chain!

1 using system; 2 using system. collections. generic; 3 using system. LINQ; 4 using system. text; 5 using system. threading. tasks; 6 7 namespace delegate2 8 {9 // declare delegate 10 public delegate void printhandler (string message); 11 12 // define delegate method of Class 1; 13 public class printprovider1 14 {15 public void print (string MSG) 16 {17 console. writeline ("++ 1" + MSG. tostring () + "++"); 18} 19} 20 // define the delegate method of Class 2; 21 public class printprovider2 22 {23 public void prinit (string MSG) 24 {25 console. writeline ("------ 2" + MSG. tostring () + "-------"); 26} 27} 28 29 class test 30 {31 // static delegate Method 32 static void staticprint (string MSG) 33 {34 console. writeline ("###### 3" + MSG. tostring () + "######"); 35} 36 37 static void main (string [] ARGs) 38 {39 string S = "delegate chain "; 40 41 // instance two printprovider class objects 42 printprovider1 PP1 = new printprovider1 (); 43 printprovider2 PP2 = new printprovider2 (); 44 45 // instance of delegate object 1 46 printhandler prn1 = new printhandler (pp1.print); 47 console. writeline ("\ n delegate instance 1 printed result:"); 48 prn1 (s); 49 50 // delegate object 2 instance 51 printhandler prn2 = new printhandler (pp2.prinit ); 52 console. writeline ("\ n delegate instance 2 printed result:"); 53 prn2 (s); 54 55 // delegate object 3 instance 56 printhandler prn3 = new printhandler (test. staticprint); 57 console. writeline ("\ n delegate instance 3 printed result:"); 58 prn3 (s); 59 60 // delegate chain Added 61 console. writeline ("\ n result of delegated instance PRN + prn2:"); 62 printhandler PRN = prn1 + prn2; 63 PRN (s); 64 65 console. writeline ("\ n delegate instance PRN + prn2 + prn3 Result:"); 66 PRN + = prn3; 67 PRN (s); 68 69 // delegate remove 70 console. writeline ("\ n delegated instance prn1 + prn3"); 71 PRN-= prn2; 72 PRN (s); 73 74 console. writeline ("\ n delegated instance prn3"); 75 PRN-= prn1; 76 PRN (s); 77 78 console. writeline ("\ n attempts to call an empty delegate chain to cause an exception"); 79 Try 80 {81 // delegate remove 82 // PRN = (printhandler) delegate. remove (PRN, new printhandler (pp1.print); 83 PRN-= prn3; 84 PRN (s); 85} 86 catch (nullreferenceexception ex) 87 {88 console. writeline (ex. message); 89} 90 91 console. writeline ("\ n attempts to remove the delegate from the null delegate chain, invalid"); 92 try 93 {94 PRN-= PRN; 95 PRN (s ); 96} 97 catch (nullreferenceexception ex) 98 {99 console. writeline (ex. message); 100} 101 102 console. readline (); 103} 104 105} 106}

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Running result:

 

I hope you can learn together and continue to study anonymous delegation tomorrow.