Question

I have a couple UIViewControllers that I am trying to access an array inside my AppDelegate. When I use an IBAction UIButton and in that method I access my AppDelegate my program dies silently. Nothing in output or the debugger, it just stops. If I run it several times I can see that it is failing to access the array properly.

To investigate this problem I created a very basic app.

In my AppDelegate.h I declared and set properties for the array

#import <UIKit/UIKit.h>
@class MyViewController;
@interface MyAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
    MyViewController *viewController;
    NSArray *images;
}
@property (nonatomic, retain) NSArray *images;
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet MyViewController *viewController;`

In the AppDelegate.m I synthesised and initialized the NSArray (Also made sure the images were added to the Resources folder).

@synthesize images;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    
    images = [NSArray arrayWithObjects:
        [[NSBundle mainBundle] pathForResource:@"bamboo_nw" ofType:@"jpg"],
        .....
        nil];
    NSLog(@"init images size:%i",[images count]); 
    [window addSubview:viewController.view];
    [window makeKeyAndVisible];
    return YES;
}

In my UIViewController.h I added class, imported header file, declared, and set properties for my AppDelegate pointer.

#import <UIKit/UIKit.h>
#import "MyAppDelegate.h"
@class MyAppDelegate;
@interface MyViewController : UIViewController {

MyAppDelegate *mainDelegate;
IBOutlet UIButton mybutton;
}
@property (nonatomic, retain) MyAppDelegate mainDelegate;
@property (nonatomic, retain) UIButton *mybutton;
-(IBAction) doSomething;`

In my UIViewController.m I synthesize and assign my AppDelegate. I set up an IBAction that will log the same count of the NSArray from the AppDelegate.

#import "MyViewController.h"
#import "MyAppDelegate.h"
@implementation MyViewController
@synthesize mybutton;
- (void)viewDidLoad {
    mainDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSLog(@"vdl images size:%i",[mainDelegate.images count]);
    [super viewDidLoad];
}
-(IBAction) doSomething {

NSLog(@”ds images size:%i”,[mainDelegate.images count]);
}

I print the size of the NSArray in the AppDelegate when I create it, in the ViewController when I first assign my AppDelegate pointer, and then as a result of my IBAction.

I find that everytime I hit the button the program dies. On the third time I hit the button, I saw that it ran my IBAction but printed my array size as 1 instead of 8. Am I missing something? Also, why don’t I get stack traces or anything, the debugger just dies silently?

Thanks in advance for any help!

Debugger Console output for 3 runs:

[Session started at 2010-05-10 06:21:32 -0700.]
2010-05-10 06:21:44.865 My[59695:207] init images size:8
2010-05-10 06:21:47.246 My[59695:207] vdl images size:8

[Session started at 2010-05-10 06:22:15 -0700.]
2010-05-10 06:22:18.920 My[59704:207] init images size:8
2010-05-10 06:22:19.043 My[59704:207] vdl images size:8

[Session started at 2010-05-10 06:22:23 -0700.]
2010-05-10 06:22:25.966 My[59707:207] init images size:8
2010-05-10 06:22:26.017 My[59707:207] vdl images size:8
2010-05-10 06:22:27.814 My[59707:207] ds images size:1

Answer 1

You need to use self.images as your lvalue in application:DidFinishLaunchingWithOptions:, to wit:

@synthesize images;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions(NSDictionary *)launchOptions {    
    self.images = [NSArray arrayWithObjects:
        [[NSBundle mainBundle] pathForResource:@"bamboo_nw" ofType:@"jpg"],
        .....
        nil];
    NSLog(@"init images size:%i",[images count]); 
    [window addSubview:viewController.view];
    [window makeKeyAndVisible];
    return YES;
}

When you use the ivar images without the self, you are giving up the goodness of the automatic retention that you set up when you created the @property.