Question

I create one protocol method and I want to implement the protocol method in multiple classes

@protocol XMLProtocol <NSObject>

- (BOOL) hasAllRequiredAttributes :(NSDictionary*)attributeMap;

@end

I have use this following class methods

#import "XMLProtocol.h"
@interface MachineA : NSObject<XMLProtocol>

and its implementation method I will implement the protocol method

- (BOOL) hasAllRequiredAttributes:(NSDictionary *)attributeMap {
  return false;
  }

and also i use this protocol method in another class

#import "XMLProtocol.h"
@interface MachineB : NSObject<XMLProtocol>

and its implementation method I will implement the protocol method

- (BOOL) hasAllRequiredAttributes:(NSDictionary *)attributeMap {
  return false;
 }

my thought is where should I call the protocol method. I totally confused. How can i do this.

Answer 1

One way you can define a global implementation for your protocol method (if I understand correctly what you are asking) is defining a category on NSObject:

@implementation NSObject (XMLProtocol)

- (BOOL) hasAllRequiredAttributes:(NSDictionary *)attributeMap {
   return false;
}

By doing like this every object will have that method. Don’t know if this is sensible, but it’s a way.

Another way would be defining a Machine base class from which both MachineA and MachineB derive; the protocol method would be defined in the base class:

@interface Machine : NSObject <XMLProtocol>
   ...
@implementation Machine
- (BOOL) hasAllRequiredAttributes:(NSDictionary *)attributeMap {
   return false;
}
    ....
@end

@interface MachineA : Machine
 ...

and any derived class could redefine it, if required.

This is not as “global” as the NSObject category, but it might be a better solution if you can define a base class for all the classes that need implement that protocol.