Question

So I’m having problems releasing some view controllers.
In essence the dealloc for the PhotoPostViewController never seems to get called, so I can’t clear down the images contained within that are munching all the memory.

This is my UIViewController subclass, I can have up to 100 of these at any one time added as subviews to the main scroll view, the iPad gets tight for memory after that.

@interface PhotoPostViewController : UIViewController {
    IBOutlet UIImageView *backgroundImage;
    IBOutlet UIImageView *serviceImage;
}

Then in my main view class I have a method to create these views and add them to a scrollView. This method is typically called from a loop to create all the subviews I need.

- (void) addPost {
    PhotoPostViewController *postView = [[PhotoPostViewController alloc] initWithNibName:@"PhotoPostViewController" bundle:nil];
    [scrollView addSubview:[postView view]];
    [viewControllers addObject:postView];
} 

viewControllers is an NSMutableArray created in the main class init.
scrollView is a UIScrollView on my main view.

This all works fine, I know the limit of the memory usage on the iPad and keep within that at any given time, opening Popovers to give preview images and videos etc…
Doesn’t run out of memory until I try to refresh the screen.
The code to do this is:

- (IBAction)didPressRefresh:(id)sender {
    for(UIView *subview in [scrollView subviews]) {
        [subview removeFromSuperview];
    }
    for(UIViewController *c in viewControllers) {
        [c release];
    }
    [viewControllers removeAllObjects];
}

For the sake of simplicity I clear off all the subviews and try to release them before recreating the next set of subviews using the function above.
It removes them from the view, but runs out of memory adding the new set of view controllers. In my test cases the sets of view controllers are identical in content, so if it loads from clean first time, then it should load the second time and every other time after that if I release everything properly.

What actually happens is it crashes due to low memory when creating the second set of view controllers.

While debugging I’ve put breakpoints on the ‘viewDidUnload’ and ‘dealloc’ methods, but they never get hit.

It looks like the UIViewController itself is getting released, yet the UIImageViews within are not, clearly they’d usually get released by my code in the dealloc (or viewDidUnload) method.

So I’m confused.
Counting things it looks to me like the reference counts are fine. so how come the dealloc is not getting hit ?

Andi

Answer 1

You need to send the postView object the -release message after adding it to the viewControllers collection:

- (void) addPost {
   PhotoPostViewController *postView = [[PhotoPostViewController alloc] initWithNibName:@"PhotoPostViewController" bundle:nil];
   [scrollView addSubview:[postView view]];
   [viewControllers addObject:postView];
   [postView release];
} 

The reason why you need to do this is because the collection sends the -retain message to all objects that are added to it, hence the memory leak and -dealloc not being hit.

EDIT:

Your -didPressRefresh: method should look like this:

- (IBAction)didPressRefresh:(id)sender {
    [[scrollView subviews] makeObjectsPerformSelector:@selector(removeFromSuperview)];     
    [viewControllers removeAllObjects];
}