Simple UITableView memory leak

Question

I have a problem with a memory leak in a simple app. The code is taken from a book iPhone iOS Development Essentials. The code is as follows:

The h file

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController
<UITableViewDelegate, UITableViewDataSource>

@property (strong, nonatomic) NSArray *colorNames;
@end

and the m file

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

@synthesize colorNames;

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.colorNames = [[NSArray alloc] initWithObjects:@"blue", @"red",@"green",@"yellow", nil];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    self.colorNames = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
    } else {
        return YES;
    }
}
- (NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [self.colorNames count];
}

-(UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if(cell==nil)
    {
        cell = [[UITableViewCell alloc] 
                initWithStyle:UITableViewCellStyleDefault
                reuseIdentifier:CellIdentifier];
    }
    cell.textLabel.text = [self.colorNames objectAtIndex:[indexPath row]];
    return cell;
}

@end

Every time when I try to scroll the table using the iPhone simulator I have a memory leak of 48k. Do you have any idea where the leak is?

Answer 1

Assuming that you don't use ARC

only if @property colorNames is a retain one you need to do for example

NSArray* cArray = [[NSArray alloc] initWithObjects:@"blue", @"red",@"green",@"yellow", nil];
self.colorNames = cArray;
[cArray release];

in addition autorelease your cell once created.

if(cell==nil)
{
     cell = [[[UITableViewCell alloc] 
                initWithStyle:UITableViewCellStyleDefault
                reuseIdentifier:CellIdentifier] autorelease];
}

Edit If you click on that memory leak, instruments can bring you to the specific line of code that creates a leak.

Hope it helps.

Answer 2

I have the same problem, already posted a bug report. Support answered me that they are aware of the problem, the Bug is still in open state and the ID is #10703036.

Still waiting even after the 4.3.2 update for Xcode...

Answer 3

Instead of @synthesize colorNames you should use:

@synthesize colorNames = _colorNames;

This creates an ivar names _colorNames .

Now use:

_colorNames = [[NSArray alloc] initWithObjects:@"blue", @"red",@"green",@"yellow", nil];

The problem with using self.colorNames = [[NSArray ... is that your property colorNames gets double retained. Once by the attribute (strong) of you property and once by calling 'alloc'.

In viewDidUnload you should use:

[_colorNames release];
_colorNames = nil;

Answer 4

Browsing different forums I've found the answer (I hope). Since the leak is from lib system_c.dlib and responsible frame strdup, people claim it's a bag in Apple library. The same problem was found with UIPickerView, UIDatePicker and UIScrollView controllers. The same size (48 Bytes), the same library and the same frame.