IOS application - define protocol in separate file - objective-c

Question

I have defined a protocol in a separate file (myProtocol.h). Here is the code for it:
#import <Foundation/Foundation.h>
#protocol myProtocol <NSObject>
-(void) loadDataComplete;
#end
Now I want to call this method so I have done the following code:
firstViewController.h:
#import "myProtocol.h"
#interface firstViewController : UIViewController{
id <myProtocol> delegate;
}
#property (retain) id delegate;
-(void) mymethod;
firstViewController.m
#implementation firstViewController
#synthesize delegate;
- (void)viewDidLoad {
[self mymethod];
}
-(void) mymethod {
//some code here...
[delegate loadDataComplete];
}
I have another file where the protocol is also utilized:
secondViewController.h:
#import "myProtocol.h"
#interface secondViewController : UIViewController<myProtocol>{
}
secondViewController.m:
-(void) loadDataComplete{
NSLog(#"loadDataComplete called");
}
but my secondViewController is not calling the protocol methad. Why is it so? Any suggestion will be appreciated.

Answer 1

First, as #Abizern suggested, try to reformat your code a little bit. Use capital letter for classes. Said this here the solution for your answer.
This is the protocol. I would name it like FirstViewControllerDelegate since the class that implements the object is a delegate for FirstViewController.
#import <Foundation/Foundation.h>
#protocol MyProtocol <NSObject>
- (void)doSomething;
#end
This is SecondViewController.
#import <UIKit/UIKit.h>
#import "MyProtocol.h"
#interface SecondViewController : UIViewController <MyProtocol>
#end
#implementation SecondViewController
// other code here...
- (void)doSomething
{
NSLog(#"Hello FirstViewController");
}
#end
This is FirstViewController.
#import <UIKit/UIKit.h>
#interface FirstViewController : UIViewController
// it coud be better to declare these properties within a class extension but for the sake of simplicity you could leave here
// the important thing is to not declare the delegate prop with a strong/retain property but with a weak/assign one, otherwise you can create cycle
#property (nonatomic, strong) SecondViewController* childController;
#property (nonatomic, weak) id<MyProtocol> delegate;
#end
#implementation FirstViewController
// other code here...
- (void)viewDidLoad
{
[super viewDidLoad];
self.childController = [[SecondViewController alloc] init];
self.delegate = self.childController; // here the central point
// be sure your delegate (SecondViewController) responds to doSomething method
if(![self.delegate respondsToSelector:#selector(doSomething)]) {
NSLog(#"delegate cannot respond");
} else {
NSLog(#"delegate can respond");
[self.delegate doSomething];
}
}
#end
For the sake of completeness, be sure to understand the delegate pattern means. Apple doc is your friend. You could take a look at the-basics-of-protocols-and-delegates to have a basic intro on the argument. Furthermore, SO search allows you to find a lot of answers on the topic.
Hope that helps.