. NET Advanced Series (8)-Delegates and Events (ii)

I. Generic delegates

　　The so-called generic delegate, that is, the parameters of a custom delegate can be constrained by generics, while the built-in delegate Func and the action itself are generic delegates.

　　Re-implement the methods in the Calculator class in the previous section with custom generic delegates.

1   Public classCalculator22     {3         //Traditional Solution One: Declare multiple methods in this class, namely, the method of doubling, square, cubic4 5 6         //Traditional Solution Two: Declare a universal method in this class, by passing different parameter types to distinguish whether to perform double or square or cubic operations7 8 9         //Solution Three: Declare a universal method, passing a delegate in, equivalent to passing a business logic, in the method only need to executeTen         /// <summary> One         ///Universal Method A         /// </summary> -         /// <param name= "Arrs" >an array of type int</param> -         /// <param name= "Mydel" >Custom Delegate</param> the          Public DelegateT mydel<t>(T t); -          Public Static voidMyspecmethord<t> (t[] Arrs, mydel<t>Mydel) -         { -              for(inti =0; I < Arrs. Length; i++) +             { -Arrs[i] =Mydel (Arrs[i]); +                 //Arrs[i] = Mydel.  Invoke (Arrs[i]); //It's equivalent to the above sentence . A Console.WriteLine (Arrs[i]); at             } -         } -  -}

Two. Built-in delegate

　　The. Net Framework provides two built-in delegates that support generics, namely action and Func, combined with lambda expressions, to improve development efficiency

The difference between the two:

1.Action can only delegate methods that have no return value, support 16 overloads (in represents an input parameter, and the overload has no return value)

respectively:

* Public delegate void Action<in t> (T obj);

* Public delegate void Action<in T1, in t2> (T1 arg1, T2 arg2);

* ......

* Public delegate void Action<in T1, in T2,......, in t16> (T1 arg1, T2 arg2,......, T16 arg16);

*

2.Func must delegate a method with a return value that supports 17 overloads (note that the last of the parentheses represents the return value, in represents the input parameter, and out represents the return value)

respectively:

* Public Delegate TResult Func<out tresult> ();

* Public delegate TResult Func<in T, out tresult> (t arg);

* Public delegate TResult Func<in T1, in T2, out tresult> (T1 arg1, T2 arg2);

* ......

* Public delegate TResult Func<in T1, in T2,....... on T16 out tresult> (T1 arg1, T2 arg2,...... T16 arg16);

*

Summary: In addition to the ref parameter and out parameters, the built-in delegate can basically be applied to any generic delegate scenario, very useful

3. The difference between the built-in delegate and the custom delegate:

A custom delegate needs to be declared to let the system know the custom delegate before the assignment method can be instantiated, and the built-in delegation system has the ability to do so, without having to declare it beforehand and instantiate the assignment method directly.

Three. Other properties of the Commission

Four. Events

. NET Advanced Series (8)-Delegates and Events (ii)