Calling protocol method with multiple subview hierarchy - iphone

Question

I am fairly new to Obj-C and learning about using protocols and delegates.
I have no trouble following examples to implement a protocol/passing data when there are only two views, however, I am getting an "unrecognized selector" error when I try to call a method when I have several subviews.
For example, in a scenario where I have
FirstViewController
SecondViewController
ThirdViewController
I would like ThirdViewController to call back to the FirstViewController.
Generic code would be something like:
in FirstViewController.h
#interface FirstViewController : UIViewController <MyProtocol>
in firstViewController.m
//present a second controller which will control settings for the app
SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:#"secondViewController" bundle:nil];
secondViewController.delegate= self;
secondViewController.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController: secondViewController animated: YES];
and later
-(void) aMethod{
//carry out some action here
}
in secondViewController.m
//present a third controller...maybe a table view for selecting music
ThirdViewController *thirdViewController = [[ThirdViewController alloc] initWithNibName:#"thirdViewController" bundle:nil];
thirdViewController.delegate= self;
thirdViewController.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController: thirdViewController animated: YES];
in ThirdViewContoller.h
//Create a protocol to implement options back on the firstViewController
#protocol MyProtocol;
#interface thirdViewController
{
IBOutlet UIButton *aButton;
}
#property (nonatomic, weak) id<MyProtocol> delegate;
-(IBAction) callMethod:(id)sender;
#end
#protocol MyProtocol <NSObject>
- (void) aMethod;
#end
in ThirdViewController.m
#synthesize delegate;
-(IBAction) callMethod:(id)sender{
[self.delegate aMethod];
}
When running it appears that the message is only sent back to secondViewController and not to the firstViewController because the error is:
-[SecondViewController aMethod:]: unrecognized selector sent to instance 0x19d620
I think there is something fundamental concept with setting delegate outlets that haven't learned yet, or the structure of the program is wrong.
There are numerous examples of code using only two view that work well here, but i haven't found much info on a multiple views. I apologize in advance if my program design is really incorrect.

Answer 1

You need SecondViewController to conform to your protocol:
#interface SecondViewController : UIViewController <MyProtocol>
You're trying to call a method on the second view controller that only exists in the first. If you want to communicate back to the first view controller, then you'll have to define a second protocol to do that.
This is a really good academic exercise to learn about the capabilities and limitations of protocols, but you should also notice the conflict in naming. Try to be as descriptive as possible when naming your protocols. Ideally, you'd have a set of header files that looked like this:
#interface FirstViewController : UIViewController <SecondViewControllerDelegate>
#end
And the second view controller:
#protocol SecondViewControllerDelegate <NSObject>
-(void)someSecondViewControllerDelegateMethod;
#end
#interface SecondViewController : UIViewController <ThirdViewControllerDelegate>
#protocol (nonatomic, weak) id <SecondViewControllerDelegate> delegate;
#end
And finally, the third view controller:
#protocol ThirdViewControllerDelegate <NSObject>
-(void)someThirdViewControllerDelegateMethod;
#end
#interface ThirdViewController : UIViewController
#protocol (nonatomic, weak) id <ThirdViewControllerDelegate> delegate;
#end
So the second view controller could implement -(void)someThirdViewControllerDelegateMethod and it could look like:
-(void)someThirdViewControllerDelegateMethod
{
[self.delegate someFirstViewControllerDelegateMethod];
}
And that's how the third view controller could call back to the first; it sort of cascades and passes on the message.