Question

I’m a fledgling iPhone developer, so be easy on me.

I’m trying to develop a simple app that will show the time and then tick every second. I feel like I’m missing something here with memory management, but my skills are too fresh to really know what I’m missing.

I’m creating a label straight to the main window (really simple app) and trying to update the label through and NSTimer. Here is my bit of code, it’s still a little messy.

@synthesize label, theDate;
@synthesize window;

- (void)tick 
{
    theDate = [[NSDateFormatter alloc] init];
    [theDate setDateFormat:@"hh:mm:ss"];
    NSString* currentTime = [theDate stringFromDate:[NSDate date]];
    label.text = [[NSString alloc] initWithFormat:@"%d",currentTime];
    [currentTime release];
}

- (BOOL)application:(UIApplication *)application 
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions     
{
    CGRect rect = CGRectMake(10, 200, 300, 20);
    label = [[UILabel alloc] initWithFrame:rect];
    label.textAlignment = UITextAlignmentCenter;
    [self.window addSubview:label];
    [NSTimer scheduledTimerWithTimeInterval:1.0f 
                                     target:self 
                                   selector:@selector(tick) 
                                   userInfo:nil 
                                    repeats:YES];
    [self.window makeKeyAndVisible];

    return YES;
}

The @synthesize‘d ivars are @propertys in the .h file and the ivars get released in dealloc.
Thanks!

Answer 1

You have a number of memory problems here:

• You are alloc’ing theDate but not releasing it, so it’s leaking.
• You are releasing currentTime despite not having an owning reference, so you’ll likely see crashes in the autorelease pool.
• You are alloc’ing the value assigned to label.text but not releasing it; either label.text is a retaining property, in which case you are leaking that string by double-retaining it, or label.text is not retaining, in which case you are leaking the string by never releasing it (except for the very last one, in dealloc)

I’d strongly suggest you read Apple’s memory management guide.

Also, unrelated to the memory issues, you are using %d to try to show a string instead of %@, so you’ll get the numeric value of the pointer address rather than the contents of the string.