Calling methods in parent's object Works with warnings

[encryption]

Hello,

I am writing an application for the Apple iPhone / Touch. Everything is going pretty well though one thing I am doing is generating warnings. Not errors but warnings, the applications still builds, installs, and runs. Though these warnings are making me think there must be a more proper way to code the functionality that I am developing.

This is an example of what I am doing and the warnings it generates:

I have a subclassed UIViewController that adds several subviews. In some of these subviews I need the ability to have the subview call methods that are located in the UIViewController object that loaded it.

This is how I am currently doing it:

In the UIViewController's .h file I have something like this:

#import <UIKit/UIKit.h>
#import "TimedBarView.h"

@interface SomeViewController : UIViewController
{

	IBOutlet TimedBarView *timedBarSubView;
	
}

@property (nonatomic,retain) IBOutlet TimedBarView *timedBarSubView;

- (void)timedBarDone;

In the subclassed UIViewController's .m file I have something like this:

#import "SomeViewController.h"

@implementation SomeViewController

@synthesize timedBarSubView;

In this same file I have some code like this in the - (void)viewDidLoad method:

self.timedBarSubView.parent = self;

This code sets a UIViewController pointer called parent that is defined in TimedBarView.h as:

@interface TimedBarView : UIViewController
{
	UIViewController *parent;
}

@property (nonatomic, retain)	UIViewController		*parent;

- (void)updateTimerBar;

In this same file I have code in the updateTimerBar method that does this:

if (progress >= 0)
{
	[timer invalidate];		
	[self.view removeFromSuperview];

	[parent timedBarDone];
}

The line [parent timedBarDone]; in the above code is what generates the following warning:

'UIViewController' may not respond to '-timedBarDone' (Messages without a matching method signature will be assumed to return 'id' and accept '...' as arguments.)

Though, there is a matching method and it does get called and functions as expected. Does anyone have any idea of what is causing this warning and how I can have a subview call its parents methods without generating such a warning?

One example of why it's so critical that the child be able to call methods in the parent object is that this timedBarView object has a button on it that enables the user to have this subview slide off screen (except for a small button that allows it to return into full view). A subview, as far as I can tell, is oblivious as to its geometry within its parent's UIView. Secondly, it is my hope that I can write such a class so that I can create several of these objects to be used throughout my application and possibly make it part of a static library that I could link against to build other applications with. So, with this in mind the object will not know who it's parent is until the code is executed.

I know the parent pointer is not included in the the default variables like self is. I thought the way I approached this made sense and it does work, but this warning has me concerned.

Thanks in advance for reading this post and any advice you can offer.

Nick Powers

[david_david]

I think you need to learn how to use @protocol in Obj C

[encryption]

Originally Posted by david_david

I think you need to learn how to use @protocol in Obj C

OK...

If it is @protocol functionality that I need to learn then does anyone know of a good online source for learning @protocol? I've looked at it on Apple's site and the way it is described there just confuses me more each time I read about it.

Also, what is it that I am trying to do that would require @protocol? I've looked at it a bit and it seems to be quite bit more than what I need. It seems funny that such overhead would be required to do such a simple task.

Is there any downside, other than an annoyance to me when building, if I just ignore the warnings and keep doing it the way I have described?

If anyone is reading this and is fluent in using @protocol then could you please give me an example on how I would use it to allow my subview the ability to call a single method from its parent's object?

Thanks again!

Nick Powers

[david_david]

protocol in objective C is similar to java interfaces

haven't check/execute the following code.. just a skeleton


//self.timedBarSubView.parent = self;
self.timedBarSubView.delegate = self;


in TimedBarView.h

@protocol MyTestDelegate;


@interface TimedBarView : UIViewController
{
	id <MyTestDelegate> delegate;
}

@property (nonatomic, assign) id <MyTestDelegate> delegate;

@end

@protocol MyTestDelegate <NSObject>

- (void)timedBarDone;

@end

in TimedBarView.m

@synthesize delegate;


if (progress >= 0)
{
	[timer invalidate];		
	[self.view removeFromSuperview];

	[self.delegate timedBarDone];
}

-(void)dealloc{

delegate = nil;
...
}

[Mehuge]

You could fix your warning as follows:

Either make parent a SomeViewController *

SomeViewController *parent;

or in updateTimerBar as long as you know the type of parent at that point, you can cast it to the appropriate type, e.g. SomeViewController * or whatever it's type is at that time.

[(SomeViewController *)parent timedBarDone];

HOWEVER, using @protocol and a delegate would be the normal way to achieve what your doing.

@protocol TimedBarDelegate
- (void) timedBarDone:(id)sender;
@end

@interface TimedBarView : UIViewController {
      id <TimedBarDelegate> delegate;
}
@end

in SomeViewControler make it implement the TimedBarDelegate protocol

@implementation SomeViewController : UIViewController <TimedBarDelegate>

then during init after a TimedBarView is created, do

timedBarView.delegate = self;

and in dealloc (important)

timedBarView.delegate = null;
[timedBarView release];

and also add the delegate method

- (void)timedBarDone:(id)sender {
     // do whatever you need to do
}

then back in TimedBarView when you want to tell the parent (or now its delegate) something

if (progress >= 0)
{
	[timer invalidate];		
	[self.view removeFromSuperview];
	if (delegate) [delegate timedBarDone:self];
}

[encryption]

Much thanks David!

That's the clearest example I have seen to date. You should write a tutorial, if your into that kind of thing.

Anyways, just wanted to show my appreciation. Now, I'm off to give it a try. Thank goodness for snapshots in XCode!

Nick Powers

Originally Posted by david_david

haven't check/execute the following code.. just a skeleton


//self.timedBarSubView.parent = self;
self.timedBarSubView.delegate = self;


in TimedBarView.h

@protocol MyTestDelegate;


@interface TimedBarView : UIViewController
{
	id <MyTestDelegate> delegate;
}

@property (nonatomic, assign) id <MyTestDelegate> delegate;

@end

@protocol MyTestDelegate <NSObject>

- (void)timedBarDone;

@end

in TimedBarView.m

@synthesize delegate;


if (progress >= 0)
{
	[timer invalidate];		
	[self.view removeFromSuperview];

	[self.delegate timedBarDone];
}

-(void)dealloc{

delegate = nil;
...
}

[david_david]

oh.. I just forgot to say about implementing this protocol in needed class otherwise this "self.timedBarSubView.delegate = self;" won't work (thanks to Mehuge to point this...)

@implementation SomeViewController : UIViewController <MyTestDelegate>

[encryption]

Originally Posted by david_david

oh.. I just forgot to say about implementing this protocol in needed class otherwise this "self.timedBarSubView.delegate = self;" won't work (thanks to Mehuge to point this...)

@implementation SomeViewController : UIViewController <MyTestDelegate>

David,

Thanks to you and Mehuge I'm golden now. Works 100% with no warnings!

The only thing I had to change, just so others might learn from this wonderful thread, was to make SomeViewController implement the TimedBarDelegate protocol I needed this line of code:

@interface SomeViewController : UIViewController <TimedBarDelegate>

in SomeViewController.h

and kept:

@implementation SomeViewController

in SomeViewController.m

Thanks again,

Nick Powers