Delegation in ios

Hi Kennedy,

The issue could be due the circulare reference that you have on MainViewController you are importing MusicViewController.h and in MusicViewController you are importing MainViewController.h. Try using @class instead #import, @class helps to circular reference.

Let me know if that works.

Also I let me suggest you, in your protocol method in musicViewControllerDelegate instead passing 3 parameters you could pass a object lest say "PlayingSong" as properties it will have music, artist and title in that way if you need to add more data you only add it to the model instead to stack more parameter to your delegate method.

Hi. Thanks for taking time to go through my problem.. However I have tried to use @class instead and I keep on getting the same error.. I have to include @class MainViewController; In the MusicViewController class so that I can be able to implement MainViewController's delegate but I keeps on throwing an error saying MainViewControllerDelegate can not be found.

@protocol musicViewControllerDelegate;

@protocol musicViewControllerDelegate <NSObject>

-(void)playSelectedMusic:(NSString *)music andArtist:(NSString *)artist andTitle:(NSString *)title;

@end

The first @protocol line can you remove from both viewControllers. There is no need for that

Also, It is customary for the delegate methods to have a reference to their owner as the first (or only) parameter, so call it:

-(void) musicViewController:(MusicViewController *)controller playSelectedMusic:(NSString *)music andArtist:(NSString *)artist andTitle:(NSString *)title;

When you write it like this, also remember to put

@class <yourViewController>

Before you declare the protocol

I shouldn't make any difference wether you have both or just one. But when you "I can not implement the MainViewControllerDelegate in my MusicViewController class.. ". What exactly is going wrong?

Here is a detailed description between class and import of .h file

• The line @class <you class> simply says to the compiler: if you see the name <you class> then that’s an object we’re going to be using. It doesn’t tell the compiler exactly what that object does, just that it’s an object. You’ll use @class mostly in .h files because at that point the compiler doesn’t need to know what the object’s properties and methods are, just that it exists. This is also known as a forward declaration.

  • #import "some class.h" literally adds the contents of the class file into the current file when it is being compiled. It means that when you use #import, the compiler knows everything about that object. If you want to access the properties of an object or call any of its methods, you need to use #import.

I'm pretty bad when it comes to explaining, so I'll tag Amit Bijlani here

I made a simple delegate example on my own and that is working fine, So I'm having a bit of difficulty seeing where your problem is to be honest. The annoying thing is that it's probably the tiniest mistake

This discussion on Stack Overflow might help: http://stackoverflow.com/questions/13712943/forward-class-and-protocols-in-objective-c/13713973#13713973

aaaah WAIT.

In your musicViewController where you do this:

@interface MusicViewController : UIViewController <UITableViewDataSource, UITableViewDelegate,MainViewControllerDelegate>
    @property (nonatomic,weak) id<MusicViewControllerDelegate> delegate;
@end

You DO need use the import statement at the top, NOT the @ class. Because like I wrote earlier, the class only tells the viewController an object is there. But when you want to implement it's methods, you need the import statement instead.

Same logic applies to the MainViewController when you implements the MusicViewController's delegate-methods.