iPhone Developement – Objective C : Protocols
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A protocol is a group of related properties and methods that can be implemented by any class.
Protocols are nothing but interface in other language. The Protocol has only method declaration. There are optional methods and required methods. If your class adopts the protocol, then you have to implement those methods in your class.
Apple provided mainly pre-defined protocol for UIKIT framework, and we can also create over own protocols.
Steps to create a protocol:
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Give name to the protocol
# import <UIKIT/ UIKIT.H>
@protocol sample protocol;
-(void) addition; // any method declaration;
Implementation of protocols in a class:-
Like class interfaces, protocols typically reside in a
. h file:
# import <UIKIT/UIKIT .h>
# import “sample protocol’s . h”
#import “second protocol’ . h”
@ interface protocol view controller: UI view controller
<Sample protocol, second protocol>
. m file:-
# import “protocol view controller’s .h”
@ implementation protocol view controller
Note: – No need to declare a protocol method in .h file.
A selector is the name of a method. A selector, by itself doesn’t do anything. It simply identifies a method.
In objective c, selectors are used to refer name of a method. The key word for selector I “@selector”
Ex:- @ selector (method name)
Passing method as argument
[Self addition :@selector (subtraction)];
Checking whether method is present or not in the other class,
B*b = [[ B alloc]init];
If ([b respond selector: @selector (subtraction)]]
NsLog( “@” no subtraction method in the B class);
@ selector is a unique identity to recognize the method name.