Question

#import <UIKit/UIKit.h>

@protocol myProtocol <NSObject>

-(void)aMethod;

@end

@interface ViewController : UIViewController

@property (weak) id<myProtocol> dSource;

@end

I am trying to get a firm grip on Obj-c protocols, I am reading apple doc to study, few things are not clear to me. Below are the points from doc:

1. The pie chart view class interface would need a property to keep track of the data source object. (The code above, we mostly declare protocol this way, when I have protocol declared in my class why need a tracking object, Or protocol can be defined in independent class? and for that we need tracking object?)

2. By specifying the required protocol conformance on the property, you’ll get a compiler warning if you attempt to set the property to an object that doesn’t conform to the protocol.

3. If you attempt to call the respondsToSelector: method on an id conforming to the protocol as it’s defined above, you’ll get a compiler error that there’s no known instance method for it. Once you qualify an id with a protocol, all static type-checking comes back; you’ll get an error if you try to call any method that isn’t defined in the specified protocol. One way to avoid the compiler error is to set the custom protocol to adopt the NSObject protocol.

Answer 1

1. I dont understand this question
2. Correct, the property requires that the property is an id which
   conforms to your property, if you try to set it to something else
   the compiler rightly complains
3. This is because respondsToSelector: is a method on the NSObject
   protocol, so you can either have your protocol extend NSObject
   (standard), or you could declare the property as
   NSObject