C # predicate Delegation

Predicate is widely used in set search and WPF data binding. Its calling format is as follows:

Call method: predicate <Object> (method)/predicate <parameter type> (method)
1. <> it indicates generic and can accept parameters of any type.

2. The (method) method can be passed as a parameter, indicating a delegate.

3. The return type is bool, indicating success or failure.

In an example, find a specific item in emplist:

 Class  Employee {  Private   String  _ Firstname;  Private   String  _ Lastname; //  Private int _ empcode;      Private   String  _ Designation;  Public  Employee (){}  Public Employee ( String Firstname, String Lastname, String  Designation) {_ firstname = Firstname; _ lastname =Lastname; _ designation = Designation ;}  ///   <Summary>      ///  Property first name  ///   </Summary>      Public   String  Firstname {  Get { Return  _ Firstname ;}  Set {_ Firstname = Value ;}}  ///   <Summary>      ///  Property last name  ///   </Summary>      Public   String  Lastname {  Get { Return  _ Lastname ;}  Set {_ Lastname =Value ;}}  Public   String  Designation {  Get { Return  _ Designation ;}  Set {_ Designation = Value ;}} 

1. Traditional Methods

Define a search method:

Static BoolEmpsearch (employee EMP ){If(EMP. firstname ="Anshu")Return True;ElseReturn False;}
 

Using the generic find () method, find () automatically calls the empsearch method iteratively.

Predicate <employee> Pred =NewPredicate <Employee (empsearch); employee EMP= Emplist. Find (Pred );
 

2. Use the anonymous method

 
EMP = emplist. Find (Delegate(Employee e ){If(E. firstname ="Anshu")Return True;ElseReturn False;});
 

You do not need to explicitly define a method,CodeMore concise

3. Use lambda expressions

 
EMP =NewEmployee (); EMP= Emplist. Find (e) => {Return(E. firstname ="Anshu");});
 

(E) => indicates passing a parameter. The parameter type can be automatically parsed.

4. search list

 
List <employee> employees =NewList <employee>(); Employees= Emplist. findall (e) => {Return(E. firstname. Contains ("J"));});
 

5. Search Indexes

Narrow the search scope by specifying the number of start indexes and search entries

IntIndex = emplist. findindex (0,2, (E) => {Return(E. firstname. Contains ("J"));
 

Indicates that two entries are searched from index 0.

6. list commonly used comparator Delegation

Sort the following Arrays

 VaR Data = New List < Int > ();  VaR Rand = New  Random (); console. writeline ( "  Unsorted list  "  );  For ( Int I = 0 ; I < 10 ; I ++ ){  Int D = Rand. Next ( 0 , 100  ); Data. Add (d); console. Write (  "  {0} "  , D );} 

Use lampda to sort data in ascending order

 
Data. Sort (E1, E2) => {ReturnE1.compareto (E2 );});