C#_ commissioned delegate

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A delegate in C # (Delegate) is similar to a pointer to a function in C or C + +. A delegate (Delegate) is a reference type variable that holds a reference to a method. References can be changed at run time.

Delegate ( Delegate) is particularly useful for implementing events and callback methods. All delegates (Delegate) are derived from the System.Delegate class.

Declaration Delegate ( Delegate)

A delegate declaration determines the method that can be referenced by the delegate. A delegate can point to a method that has the same label as its.

1 delegate function return type delegate name (< method parameter list >);

instantiate a delegate ( Delegate)

The delegate object must be created using the New keyword and is related to a specific method. When a delegate is created, the arguments passed to the new statement are written like a method call, but without parameters.

1 New delegate type (< registration method >);

Invoking a method through a delegate instance is equivalent to executing the registration method.

anonymous function Initialization delegate

It is cumbersome to specifically define a method for initializing a delegate, typically invoking a method that assigns a value when the delegate instance is initialized, rather than invoking the method itself directly.

The format is as follows:

1 Delegate delegate (function) returns the type delegate type (function argument list); 2 3 New delegate type (delegate(< function parameter list: type parameter name, type parameter name ...>)4{5     // function Body 6 });

or omit the new keyword.

1 Delegate delegate (function) returns the type delegate type (function argument list); 2 3 Delegate (< function parameter list: type parameter name, type parameter name ...>) 4 {5     // function Body 6 };

Delegated Multicast (multicasting of a Delegate)

Delegate objects can be merged using the "+" operator. A merge delegate invokes the two delegates it merges. Only delegates of the same type can be merged. The "-" operator can be used to remove a component delegate from a merged delegate.

Using this useful feature of delegates, you can create a call list of methods to invoke when a delegate is called. This is called a delegated multicast (multicasting), also called multicast.

Multicast can be used to extend or reduce functions like data in a delegate.

1 namespace_9_delegate_2_201708012 {3     classtestdelegate4     {5          Public Static voidPRINTFA ()6         {7Console.WriteLine ("PRINTFA!");8         }9 Ten          Public Static voidPRINTFB () One         { AConsole.WriteLine ("PRINTFB!"); -         } -     } the     Delegate voidmydelegate (); -  -     class Program -     { +         Static voidMain (string[] args) -         { +             //Create a delegate instance A MyDelegate D; atMyDelegate da =Newmydelegate (TESTDELEGATE.PRINTFA); -MyDelegate db =Newmydelegate (TESTDELEGATE.PRINTFB); -D =da; -D + =db; -             //Call Multicast -Console.WriteLine ("Call Delegate instance D ==da+db:"); in d (); -D-=da; toConsole.WriteLine ("Call Delegate instance D ==db:"); + d (); -         } the     } *}

Delegate Multicast Example
Benefits of Delegation

1, the Operation function is more flexible, as the use of variables as convenient, with dynamic , you can avoid the application of a large number of branch statements.

2, compared with the function pointer in C++,c, the delegate is object-oriented, type-safe, reliable controlled object. The delegate can guarantee the address of a safe and effective storage function that does not cross over.

3. The pointer can only point to a static function when compared to a function pointer in C++,c, and a delegate may refer to a static function or a non-static member function .

A delegate can be used when a program must call a method to perform an operation, but the compilation cannot determine what method it is.

C#_ commissioned delegate