Question

Currently I have a navigation based application and obviously the RootViewController is a UITableView. However, I deemed it necessary to create a UIToolbar that floats above the UITableView. Currently I do this like this.

- (void)viewWillAppear:(BOOL)animated {

 [super viewWillAppear:animated];


 //Initialize the toolbar 
 toolbar = [[UIToolbar alloc] init]; 
 toolbar.barStyle = UIBarStyleDefault;

 //Set the toolbar to fit the width of the app. 
 [toolbar sizeToFit];

 //Caclulate the height of the toolbar 
 CGFloat toolbarHeight = [toolbar frame].size.height;

 //Get the bounds of the parent view 
 CGRect rootViewBounds = self.parentViewController.view.bounds;

 //Get the height of the parent view. 
 CGFloat rootViewHeight = CGRectGetHeight(rootViewBounds);

 //Get the width of the parent view, 
 CGFloat rootViewWidth = CGRectGetWidth(rootViewBounds);

 //Create a rectangle for the toolbar 
 CGRect rectArea = CGRectMake(0, rootViewHeight - toolbarHeight, rootViewWidth, toolbarHeight);

 //Reposition and resize the receiver 
 [toolbar setFrame:rectArea];

 //Create a button 
 UIBarButtonItem *infoButton = [[UIBarButtonItem alloc] initWithTitle:@"Settings" style:UIBarButtonItemStyleBordered target:self action:@selector(account_details)];

 [toolbar setItems:[NSArray arrayWithObjects:infoButton,nil]];

 //Add the toolbar as a subview to the navigation controller. 
 [self.navigationController.view addSubview:toolbar];
 [infoButton release];

 [self.tableView reloadData];

}

However, after using the Leaks instrument tool, I was able to determine that this was the cause for a few memory leaks, only small, but memory leaks nonetheless. I then drilled down even further and was able to pin point the exact lines that are causing the memory leaks. They are the following.

UIBarButtonItem *infoButton = [[UIBarButtonItem alloc] initWithTitle:@"Settings" style:UIBarButtonItemStyleBordered target:self action:@selector(account_details)];

 [toolbar setItems:[NSArray arrayWithObjects:infoButton,nil]];

 [self.navigationController.view addSubview:toolbar];

I am struggling to figure out how to remove these memory leaks and thus causing my application to run smoother. Any help would be appreciated as to why the above lines are causing leaks!

Answer 1

A new toolbar is created every time the view appears, added to the view and never released. This means that both that tool bar and its bar button item will last forever. You can fix this by simply releasing the toolbar after you add it to the view, or sending it the autorelease message when you create it. So, a decent way to do this would be to replace:

toolbar = [[UIToolbar alloc] init];

with:

toolbar = [[[UIToolbar alloc] init] autorelease];

Also, the way you’re doing this, every time your view appears you end up adding another toolbar to the navigation controller’s view. So you almost certainly have quite a few of these objects sitting on top of each other (so you will still see leaks until the navigation view finally goes away). What you might want to do is keep this toolbar as an ivar. When your view disappears, remove the toolbar from the nav controller’s view. When it appears, add it. Create the toolbar itself in your viewDidLoad method and clean it up in viewDidUnload then release it in dealloc. So your new class might look like this (let’s assume you create a synthesized property named toolbar that’s retain):

- (void)viewDidLoad
{
  [super viewDidLoad];
  UIToolbar* toolbar = [[[UIToolbar alloc] init] autorelease];
  // set up toolbar
  [self setToolbar:toolbar];
  // other load code
}

- (void)viewWillAppear:(BOOL)animated
{
  [super viewWillAppear:animated];
  [[[self navigationController] view] addSubview:[self toolbar]];
  // other vwa code
}

- (void)viewDidDisappear:(BOOL)animated
{
  [super viewDidDisappear:animated];
  [[self toolbar] removeFromSuperview];
}

- (void)viewDidUnload
{
  [self setToolbar:nil];
  [super viewDidUnload];
}

- (void)dealloc
{
  UIToolbar* toolbar = [self toolbar];
  [toolbar removeFromSuperview]; // shouldn't ever need this, but be safe
  [toolbar release];
  // other dealloc
  [super dealloc];
}