How to access a method by inheritance of @protocols in Objective-C?

Question

Hi,

I have a program where inheritance of protocols are there say:

@protocol A
-(void)methodA
@end

The protocol which inherits:

@protocol B<A>
-(void)methodB
@end

The class which implements @protocolA method is

@interface classB<B>

@end

@implementation classB
-(void)methodA
{
  //somecode
}
@end

Now i wanted the methodA to be called from Some other class:

    @implementation SomeotherClass

{
   //call of methodA
   //????

id<A>obj=[[classB alloc]init];//i have tried it
[obj methodA];// even this is not working 
}

How to do that?

Answer 1

Just send the message as usual:

SomeotherClass *obj = [[[SomeotherClass alloc] init] autorelease];
[obj methodA];

Since instances of classB implement protocol B, they also claim to respond to -methodA. The following compiles and runs without any problems:

MyClass.h:

#import <Foundation/Foundation.h>

@protocol A
-(void) methodA;
@end

@protocol B <A>
-(void) methodB;
@end

@interface MyClass : NSObject <B>
{
}

@end

MyClass.m:

#import "MyClass.h"

@implementation MyClass

-(void) methodA
{
    NSLog(@"%s", __PRETTY_FUNCTION__);
}

-(void) methodB
{
    NSLog(@"%s", __PRETTY_FUNCTION__);
}

@end

the code:

MyClass *obj = [[MyClass alloc] init];
[obj methodA];
[obj methodB];
[obj release];

Answer 2

You don't say how it fails to work. I would guess that there's a compilation error as you don't implement methodB in your classB.

Another possibility: what happens after you've initialised classB in SomeOtherClass? Are you sure that you get a valid object back? If it returned a nil the run time would be perfectly within its rights to do nothing when you sent the methodA message to it.