Objective-C protocol (Protocol)

The role of the Protocol is similar to the multi-inheritance of abstract base classes in C ++. Similar to the interface concept in Java.
The Protocol is a list of multiple class sharing methods,Methods listed in the Protocol are not implemented in this class, but are implemented by other classes.

If a class complies with a protocol, the class must implement all methods of the specific Protocol (except for optional methods ).

To define a protocol, you need to use the @ protocol command, followed by the protocol name, and then you can declare some methods. The declaration of all methods before the command @ end is part of the Protocol. As follows:

@protocol NSCopying-(id) copyWithZone:(NSZone*) zone;@end

If your class decides to comply with the nscopying protocol, you must implement the copywithzone method. By listing the protocol name in a pair of angle brackets in @ interface, you are told to compile a protocol, for example:
@ Interface Test: nsobject <nscopying>

Instance:
Fly. h

＃import <Foundation/Foundation.h>@protocol Fly  -(void) go;  -(void) stop;@optional  -(void)sleep；@end

Flytest. h

＃import <Foundation/Foundation.h>#import "Fly.h"@interface FlyTest:NSObject<Fly> {}@end

Flytest. m

＃import "FlyTest.h"@implementation FlyTest-(void) go {   NSLog(@"go");}-(void) stop {   NSLog(@"stop");}@end

Test. m

#import <Foundation/Foundation.h>#import "FlyTest.h"int main( int argc, char* argv[]){  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];  FlyTest *flytest = [[FlyTest alloc]init];  [flytest go];  [flytest stop];  [flytest release];  [pool drain];  return 0;}

The program running result is as follows:

Go
Stop

@ Protocol:
@ Protocol name <other protocols,...>
Method Declaration 1
@ Optional
Method Declaration 2
@ Required
Method 3
...
@ End

@ Optional indicates that the classes of the Protocol do not have to be implemented.
@ Required is a required method.