Question

This morning I ran into a crash in an iPhone app I am working on and while I fixed the bug, I’m curious about syntactic reason it was a problem.

Here is my code reduced to simple elements. I am populating items in a TableView using an NSArray for the items. The NSArray is a property:

@interface FooViewController : UITableViewController {
    NSArray *stuff;
}

@property (nonatomic, retain) NSArray *stuff;

And in my implementation file:

@synthesize stuff;

- (void)viewDidLoad {     
    NSArray *arr = [[NSArray alloc] initWithObjects:@"", @"Item 1", @"Item 2",   
                                       @"Lorem", @"Ipsum", nil];
    self.stuff = arr;

    [arr release];
}

Now, when I first wrote the method, I accidentally left off the “self.” and that caused the bomb. Although while testing, it worked at first blush. I’d tried:

stuff = arr;
NSLog(@"%d", [stuff count]);

But using stuff in other methods bombed. Now that I’ve fixed the problem, I can use [stuff count] in other places.

So why can I use stuff in some places but in others I must use self.stuff?

Answer 1

This would have also worked properly:

- (void)viewDidLoad {     
    stuff = [[NSArray alloc] initWithObjects:@"", @"Item 1", @"Item 2",   
                                       @"Lorem", @"Ipsum", nil];
}

Because the array was retained by alloc. But it’s usually better to stick to the dot notation if you have a property and use the autorelease array creation methods, where you get retains “for free” from the property:

- (void)viewDidLoad {     
    NSArray *arr = [NSArray arrayWithObjects:@"", @"Item 1", @"Item 2",   
                                       @"Lorem", @"Ipsum", nil];
    self.stuff = arr;

}

You probably just left it out to keep things simple, but you also need to free this array in dealloc:

- (void)dealloc {     
  [stuff release]; stuff = nil;
}