Question

I’m building a segmented control within my viewDidLoad method, like so:

NSArray *tabitems = [NSArray arrayWithObjects:@"ONE", @"TWO", nil];
UISegmentedControl *tabs = [[UISegmentedControl alloc] initWithItems:tabitems];
tabs.segmentedControlStyle = UISegmentedControlStyleBar;
tabs.frame = CGRectMake(185.0, 7.0, 130.0, 30.0);
tabs.selectedSegmentIndex = 0;
[self.navigationController.navigationBar addSubview:tabs];
[tabs release];

But when the user goes Back in the uinavigationcontroller hierarchy, the segmented controller stays on the navigation bar. How would I get rid of it? Or am I doing something fundamentally wrong?

---

EDIT

Following Alex’s suggestions, I propertized tabs and tried:

  NSArray *tabItems = [NSArray arrayWithObjects:@"FAQs", @"Terms", nil];
  self.tabs = [[UISegmentedControl alloc] initWithItems:tabItems];

but I’m not sure it’s a good idea to alloc a property;

And I’m using

  [self.tabs removeFromSuperview];

in my viewWillDisappear. Is that enough?

Answer 1

Retain a reference to the segmented control in your view controller (i.e define tabs as a property in the view controller’s header file).

Override the view controller’s -viewWillDisappear: method, and remove the segmented control from the navigation bar there, using the control’s -removeFromSuperview method.

EDIT

You would still alloc-init your segmented control tabs in -viewDidLoad. You just need to set up a retain property for tabs in your view controller’s header, and move the control’s release statement to the view controller’s dealloc method.

Read the “Properties” section of this Objective-C tutorial for an introduction to properties and how to set them up.

The way to override a method is as follows:

- (ReturnClass) methodNameToOverride:args {
    [super methodNameToOverride:args];
    // your code goes here...
}

In the case of -viewWillDisappear:, this method gets called when your view controller is about to disappear, such as when it gets popped off the navigation stack. This is a great place to put code that manages clean-up of view-controller-specific items, like your segmented control:

- (void) viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [tabs removeFromSuperview];
}

EDIT 2

If your property is set as follows:

@property (nonatomic, retain) UISegmentedControl *tabs;

then you are going to retain anything you set self.tabs equal to.

Your code here:

self.tabs = [[UISegmentedControl alloc] initWithItems:...];

will create a memory leak, because you are retaining this object: [[UISegmentedControl alloc] init] — but you never release [[UISegmentedControl alloc] init] itself. This is bad.

Instead, use autorelease on the right side, i.e.:

self.tabs = [[[UISegmentedControl alloc] initWithItems:...] autorelease];

The tabs property retains its own reference to the initialized segmented control. That initialized segmented control is itself released properly at some later point. So no more memory leak.