OC Language--protocol (protocol)

First, protocol1. Basic use

1> can be used to declare many methods, but cannot be used to declare member variables

2> as long as a class complies with this protocol, it is equivalent to having all the method declarations in this agreement

3> as long as the parent adheres to a protocol, the subclass also adheres to the

2. Format

Preparation of the 1> protocol

@protocol Agreement Name

Method declaration List

-(void) test;

-(void) test2;

+ (void) test;

+ (void) test2;

@end

2> a class to comply with a protocol

@interface Class Name: Parent class < protocol name >

@end

3> when defining a variable, restrict the object that the variable holds to adhere to a protocol

Class name < protocol name > variable name;

For example,:nsobject< protocol name 1> *obj;//now obj can only hold objects that comply with protocol name 1; If you do not follow the compiler will issue a critical warning

The attributes declared in the 4> @property can also be used as a restriction to comply with the protocol

Example: @property (Nonatomic,strong) class name < protocol name > * attribute name;

@property (nonatomic,strong) dog< agreement name > *dog;

3. Keywords

There are two keywords in the protocol that control whether the method is to be implemented (by default, @required), and in most cases the use of communication between programmers

1> @required: This method must be implemented (if not implemented, the compiler warns)

2> @optional: This method is not necessarily implemented

1 @protocolMyProtocol//Claim Agreement2- (void) test;3+ (void) test;4 @optional5- (void) test2;6+ (void) test2;7 @end8 9 #import<Foundation.Foundation.h>Ten  One @interfacePerson:nsobject <MyProtocol>//Compliance Agreement A @end -  - @implementation the- (void) Test - { -     //requires that the method be implemented - } ++ (void) Test - { +     //requires that the method be implemented A } at  -- (void) Test2 - { -     //the method can not be implemented - } -+ (void) Test2 in { -     //the method can not be implemented to } + } - @end the  * intMain () $ {Panax Notoginseng     return 0; -}

Agreement (example)4. Agreement to comply with agreements

1> one protocol can comply with many other protocols, with multiple protocols separated by commas,

2> a protocol complies with other agreements, it is equivalent to having a method declaration in another agreement

3> Multi-protocol format

@protocol Agreement name < Protocol 1, Protocol 2>

@end

5. Base protocol

1> NSObject is a base class, the most fundamental and basic class, and any other class will eventually inherit his

2> NSObject is also an agreement, the most fundamental and basic agreement

Many of the most basic methods are stated in the 3> NSObject protocol, such as description, retain, release, etc.

4> recommends that each new agreement be subject to the NSObject agreement

6. Attention Points

The protocol can be defined in a separate. h file, or it can be defined in a class

1> If this protocol is used only in a class, the protocol should be defined in that class

2> If this protocol is used in many classes, it should be defined in a separate file

II. application of the protocol--proxy mode 1. Design principle

Some things do not want to do themselves, you can find a person to help do, that is, to the agent to do

2. Design principles

1> first to have a proxy object property

2> second to understand what the agent has

3> finally to help decouple

3. Implementation scenarios

1> defines a protocol in which to declare some methods of communicating with the agent

2> has a proxy attribute id<protocol>delegate

3> Let Agent obey protocol

1 #import<Foundation.Foundation.h>2 3@property ticketdelegate <NSObjecct>//Design Protocol4- (Double) Ticketprice;//Fares5-（int) Leftticketnumber;//number of votes left6 @end7 8 9 @interfacePerson:nsobjectTen  One@propertyID<TIcketDelegate>Delegate; A  -- (void) Buyticket; -  the @end -  -  -  + @implementation Person -  +- (void) Buyticket A { at     //I have no time to buy tickets, call Agent -     DoublePrice =[_delegate Ticketprice]; -     intNumber =[_delegate Leftticketnumber]; -NSLog ("through the agent, the fare =%d, the remaining number of votes is%d", price, number); - } - @end in  -  to  +  - @interfaceAgent <TicketDelegate>//Compliance Agreement the @end *  $ Panax Notoginseng  - @implementationAgent:nsobject the- (Double) Ticketprice + { ARerurn100.0; the } +  --（int) Leftticketnumber $ { $     return Ten; - } - @end the  - Wuyi  the intMain () - { WuPerson *p = [personNew];//people -Agent *a = [AgentNew];//Agent About  $P.Delegate= A;//set up agents for people - [P buyticket]; -  -     return 0; A}

Proxy (example)

OC Language--protocol (protocol)