autorelease pool - iphone

Question

I was hoping someone could help me with a memory issue on the iPhone.
I have a scrollview that is part of a nav controller.
Whenever I first push the nav controller and scroll through the scrollview (adding images as I go), memory is allocated in huge chunks (say 1mb each).
If I rotate the display a couple of times, the memory is freed, and everything is fine: The scrollview works correctly and the memory returns to where it should be (around 1mb, looking at the Net alloc in Instruments).
How can I keep the memory from going wild, or free it up during use of the scrollview, just as the device rotation does?
Here is the code snippet that is called to load the scrollview page:
- (void)loadPage:(int)page isCurrent:(BOOL)isCurrent {
if (page < 0) return;
if (page >= totalRows) return;
picViewController *controller = [[picViewController alloc] init];
if ((NSNull *)[viewControllers objectAtIndex:page] == [NSNull null]) {
NSString *fullPath = [self fullPath];
if([fileManager fileExistsAtPath:fullPath]) {
currentImage=[UIImage imageWithContentsOfFile:fullPath];
[controller setImg:currentImage];
[viewControllers replaceObjectAtIndex:page withObject:controller];
}
else {
AsyncImageView* asyncImage = [[AsyncImageView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]];
asyncImage.tag = 8;
[asyncImage loadImageFromName:imageName withURL:url];
[controller.view addSubview:asyncImage];
[asyncImage release];
[viewControllers replaceObjectAtIndex:page withObject:controller];
}
if (nil == controller.view.superview) {
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
controller.view.frame = frame;
[scrollView addSubview:controller.view];
}
[controller release];
}
}

Answer 1

I don't see where in your code you're actually purging off-screen pages.
Your code is somewhat like Apple's PageControl example, right?
What I do is loop through the pages each time a page is "activated" and purge pages more than 1 or 2 screens away. (1 for without bounce scrolling, 2 for with.)
- (void)updateCachedPages {
int active = pageControl.currentPage;
int count = pageControl.numberOfPages;
for ( int i = 0; i < count; i++ ) {
if ( abs( active - i ) <= 2 ) {
[self loadPage:i];
}
else {
[self purgePage:i];
}
}
}
- (void)purgePage:(int)page {
if ((page < 0) || (page >= [_myObjects count])) return;
MyControllerClass *controller = [_viewControllers objectAtIndex:page];
if ((NSNull *)controller != [NSNull null]) {
[_viewControllers replaceObjectAtIndex:page withObject:[NSNull null]];
//NSLog( #"Purged page %d", page );
}
}
Call updateCachedPages in scrollViewDidEndDecelerating, your PageControl's page change action, and viewWillAppear.

Answer 2

does your controller pay attention to memory low notifications? You could flush any images which aren't visible when that's received, or do any other releasing you think relevant.

Answer 3

OK, I wasn't freeing all the memory after all.
Once I found a class instance not being freed properly, and made sure tewha's purge code was working, everything is golden.
Thanks for the quick help. This forum is awesome BTW.