[Solved] how delegates works and delegates work flow in objective-c

Question

First of all let me point out that you do not need to create a separate instance variable with an underscore prefix when you use @property to declare a property. You can access this property using self.delegate and it also automatically creates _delegate for you. Because _delegate is already created using @property you can take out the duplicate declaration.

Secondly, you can move <SampleProtocolDelegate> to the property declaration, you should also set it to weak to avoid a retain cycle. See: Why use weak pointer for delegation?. So your interface would end up looking like this:

@interface SampleProtocol : NSObject

@property (nonatomic, weak) id <SampleProtocolDelegate> delegate;

-(void)startSampleProcess;

@end

By putting <SampleProtocolDelegate> between ‘id’ and ‘delegate’,
only objects that conform to the SampleProtocolDelegate can set themselves as the delegate of the object (it means: any object that conforms to this protocol). And the SampleProtocol object can safely assume that it can call the protocol methods on its delegate.

Accepted Answer

First of all let me point out that you do not need to create a separate instance variable with an underscore prefix when you use @property to declare a property. You can access this property using self.delegate and it also automatically creates _delegate for you. Because _delegate is already created using @property you can take out the duplicate declaration.

Secondly, you can move <SampleProtocolDelegate> to the property declaration, you should also set it to weak to avoid a retain cycle. See: Why use weak pointer for delegation?. So your interface would end up looking like this:

@interface SampleProtocol : NSObject

@property (nonatomic, weak) id <SampleProtocolDelegate> delegate;

-(void)startSampleProcess;

@end

By putting <SampleProtocolDelegate> between ‘id’ and ‘delegate’,
only objects that conform to the SampleProtocolDelegate can set themselves as the delegate of the object (it means: any object that conforms to this protocol). And the SampleProtocol object can safely assume that it can call the protocol methods on its delegate.