数据未持久存在于同一对象的多个实例中（iOS）

Question

I'm having issues with data persisting inside of multiple instances of objects I'm creating.

I have a class "IconViewController" that extends UIViewController that I pass information to, such as the name of the image it should be using:

//IconViewController.h

@interface AppIconViewController : UIViewController
{
    NSString *imageName;
}

@property (nonatomic, retain) NSString *imageName;

- (void) doSomething;


//IconViewController.m

@implementation AppIconViewController

@synthesize imageName;

NSNumber *iconWidth;

- (void)loadView
{
    [super loadView];

    UIImageView *iconImage = [[UIImageView alloc] initWithImage:[UIImage imageNamed:imageName]];
    iconWidth = [NSNumber numberWithFloat:iconImage.bounds.size.width];
    [iconImage release];

    NSLog(@"iconWidth: %f", [iconWidth floatValue]);
}

- (void) doSomething
{
    NSLog(@"iconWidth: %f", [iconWidth floatValue]);
}

In another view controller, I'm instantiating several instances of these IconViewControllers and passing different sized images to them:

AppIconViewController *appIcon1 = [[AppIconViewController alloc] initWithNibName:nil bundle:nil];
appIcon1.imageName = @"Image65PXWide.png";
[self.view addSubview:appIcon1.view];

AppIconViewController *appIcon2 = [[AppIconViewController alloc] initWithNibName:nil bundle:nil];
appIcon2.imageName = @"Image105PXWide.png";
[self.view addSubview:appIcon2.view];

Okay, the weirdness is that when I'm creating these, I'm getting logs back that are accurate...appIcon1 logs "iconWidth: 65.0" and appIcon2 logs "iconWidth: 105.0". But when I call:

[appIcon1 doSomething];

...my log is "iconWidth:105.0".

Why is the data in the first instance reflecting the data in the second instance? What am I missing?

EDIT:
I know that if I declare iconWidth in the header and synthesize it as a property, that it will work. So what I'm wondering is how to make a private version of it persist. Because I tried retaining the NSNumber with:

iconWidth = [[NSNumber numberWithFloat:iconImage.bounds.size.width] retain];

...and it still doesn't work. Does it have to be synthesized and public?

EDIT #2:
Okay, so I figured out that once I declare iconWidth in my header, it works just fine, and I don't have to synthesize it so it keeps it private. Not sure why exactly it won't work if declared in the implementation file - does anyone have any insight into why and if there's any purpose in declaring variables at the top of an implementation but not in the header? Just curious now more than anything.

Answer 1

In your method doSomething, you are assuming iconWidth is set up properly.

However, iconWidth is created as an autorelease object in loadView method, so when loadView finishes, the main loop will release iconWidth and you are getting random values.

To fix this you have to retain iconWidth so you can use it in other methods

iconWidth = [[NSNumber numberWithFloat:iconImage.bounds.size.width] retain];

As a general rule, method that doesn't start with init will return autorelease object, so you have to be careful how you instantiate an object and whether you need to call retain on it.

Answer 2

Synthesizing doesn't make anything private. It just generates getter/setter methods according to declared properties.

By placing iconWidth in the implementation, outside of any methods, it's essentially a class-level variable. So it gets overwritten by the last thing that writes to it. You already have imageName declared in the interface, so why not just put iconWidth there as well (instance variables are private by default)?