Dark Horse programmer-oc-about the Protocol

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Protocol protocol

1, Protocol agreement is used to declare the method.

2, as long as a class to comply with a certain agreement, you can have the agreement of all the method statement

3.: Inherit parent class

4. <> Compliance Agreement

5, the protocol can not write implementation and member variables, the suffix of the protocol file is. h (Declaration file).

1. Definition of the Agreement

@protocol Agreement name <NSObject>

Method declaration List ....

@end

For example:

1 #import <Foundation/Foundation.h>23@protocol myprotocol <nsobject >   //  Declare an agreement which complies with the base agreement 45 -(void) test; 6 7 @end

2. How to comply with the agreement

1> Class Compliance Agreement

@interface Class Name: Parent class name < protocol name 1, protocol name 2>

@end

2> Protocol Compliance Agreement

@protocol Agreement name < Other protocol name 1, other protocol name 2>

@end

3> Base protocol

NSObject is a base class, the most fundamental and basic class, and any other class will eventually inherit it .

There is also a protocol named NSObject, which is a base protocol, the most fundamental and basic protocol

The NSObject protocol declares many basic methods, such as description,retain,release, etc.

It is recommended that each new agreement be subject to the nsobject agreement .

3. Keywords for method declarations in the agreement

1> @required (default) // writing facilitates communication between programmers

Requires implementation, and if not implemented, a warning is issued

2> @optional

Does not require implementation, how can there be no warning

For example:

1 #import<Foundation/Foundation.h>2 3 @protocolMyProtocol <NSObject>4 5- (void) test4;6 7 @required8 9- (void) test;Ten  One @optional A  -- (void) test3; -  the @end

4. When defining a variable, limit the object that this variable holds to a protocol

Class name < protocol name > * variable name;

id< protocol name > variable name;

1 nsobject<myprotocol> *obj; 2 3  ID<MyProtocol> obj2; 4 5  nsobject<myprotocol> *obj = [[Person alloc] init];

Where the person must have complied with the MyProtocol protocol.

If the corresponding protocol is not followed, the compiler warns

The attributes declared in [email protected] can also be used as a limit to comply with the agreement

@property (nonatomic, Strong) class name < protocol name > * attribute name;

@property (nonatomic, strong) id< protocol name > attribute name;

1 @property (nonatomic, Strong) dog<myprotocol> *Dog; 2 3  ID<MyProtocol> dog2;

6. The agreement can be defined in a separate. h file and can also 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

7. Classifications can be defined in separate. h and. m files and can also be defined in the original class

1> in general, are defined in a separate file

2> defines the classification in the original class, only requires the ability to read the grammar

Protocols are generally used in proxy mode and Observer mode.

Proxy design mode

Design principle

Some troublesome things do not want to do it yourself, you can find someone to help do, that is, to the agent to do

Design principles

You first have to have a proxy object property

Second, it's important to know what the agent means.

Finally, be sure to decouple

Implementation scenarios

Define a protocol protocol name Ticketdelegate, in which you declare some ways to communicate with the agent

has a proxy attribute id<ticketdelegate> delegate

agent's class name whatever, must abide by the ticketdelegate agreement

Note:@property (nonatomic, retain) ID <TicketDelegate> delegate

Let the agent comply with ticketdelegate

Dark Horse programmer-oc-about the Protocol