UIScrollView doesn't release images

Question

I have a UIScrollView that shows a gallery of images from a plist file. I also have a function to delete an image from the gallery image list that basically deletes an object in the plist file and then reload the images in the ScrollView. The issue is I am not able to release the images of the UIScrollView before to reload it with the new content when I use the method - (IBAction)deleteimage:(id)sender. The new content is loaded but over the older content and then the images are still behind the new one. What I should do to release images before to reload the scrollview content?

The code I am using is :

#import "ImageScrollViewController.h"

@interface ImageScrollViewController ()

@end

@implementation ImageScrollViewController

@synthesize images,scrollView,pageControl,subview;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
    // Custom initialization
}
return self;
}

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
scrollView.autoresizingMask = ( UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);

[self setupthescroll];
self.pageControl.currentPage = 0;
}

- (void)setupthescroll{

//Get the images of the Array
NSUserDefaults *success = [NSUserDefaults standardUserDefaults];
images = [success mutableArrayValueForKey:@"imagelist"];
NSLog(@"list of images%@",images);

pageControlBeingUsed = NO;

for (int i = 0; i < images.count; i++) {
    CGRect frame;
    frame.origin.x = self.scrollView.frame.size.width * i;
    frame.origin.y = 0;
    frame.size = self.scrollView.frame.size;

    subview = [[UIImageView alloc] initWithFrame:frame];
    NSString *str4 = [images objectAtIndex:i];
    subview.image = [[[UIImage alloc] initWithContentsOfFile:str4] autorelease];
    self.subview.contentMode = UIViewContentModeScaleAspectFit;
    [self.scrollView addSubview:subview];
    [subview release];
}

self.scrollView.contentSize = CGSizeMake(self.scrollView.frame.size.width * images.count, self.scrollView.frame.size.height);

self.pageControl.numberOfPages = images.count;

//Get the number of the images
int page;
page = self.pageControl.currentPage;
printf("Current Page: %d", page);

}

- (void)scrollViewDidScroll:(UIScrollView *)sender {
if (!pageControlBeingUsed) {
    // Switch the indicator when more than 50% of the previous/next page is visible
    CGFloat pageWidth = self.scrollView.frame.size.width;
    int page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
    self.pageControl.currentPage = page;
}
}


- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
pageControlBeingUsed = NO;
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
pageControlBeingUsed = NO;
}

- (IBAction)changePage {
// Update the scroll view to the appropriate page
CGRect frame;
frame.origin.x = self.scrollView.frame.size.width * self.pageControl.currentPage;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}

- (IBAction)deleteimage:(id)sender{
//Get the number of the image
int page;
page = self.pageControl.currentPage;
printf("Current Page: %d", page);

//Remove the images of the Array
NSUserDefaults *success = [NSUserDefaults standardUserDefaults];
images = [success mutableArrayValueForKey:@"imagelist"];
[images removeObjectAtIndex:page];
NSLog(@"list of images%@",images);

//Update the Array
NSUserDefaults *arrayofimages = [NSUserDefaults standardUserDefaults];
[arrayofimages setObject:images forKey:@"imagelist"];

//Refresh the ScrollView
[self setupthescroll];

//post the notification than images have been updated
NSUserDefaults *deleted = [NSUserDefaults standardUserDefaults];
[deleted setObject:@"deleted" forKey:@"deletedimages"];
}

- (IBAction)closepage:(id)sender{
[self dismissModalViewControllerAnimated:YES];
}

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

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

- (void)dealloc {
[pageControl release];
[scrollView release];
//[images release];
[super dealloc];
}

@end

Answer 1

You forgot to remove the previous image views from the scrollView subviews. A brutal method to to this (at least for testing the hypothesis) would be to add the following line at the beginning of setupthescroll:

[self.scrollView.subviews makeObjectsPerfomSelector:@selector(removeFromSuperview)];

The problem with this would be that the scrollview's private subviews ( scrollers, for instance ) would be removed too. So in practice you should keep track of the subviews you created in an ivar array, and perform the above line on this array instead of the subviews array, and clear the array afterwards.

Alternatively, a much cleaner method would be to delete only the subview corresponding to the deleted image, and to update the frames of the remaining image views, instead of deleting and recreating everything. You could use a dictionary or the subviews tag property to keep track of wich view is associated to which image.

Answer 2

If you are reloading the entire scrollview (i.e. adding all the images back), you first need to remove the existing images.

Use UIView's removeFromSuperview method to remove views from the scrollview.

So a code snippet to remove all image views from the scrollview would look something like this

NSArray *imgViews = [scrollView subviews];
for(id aView in imgViews){
    if([aView isKindOfClass:[UIImageView class]]){
      [aView removeFromSuperview]; //remove only if its an imageview
    }
}

If you already have reference to the image views, you can directly call the method on them without iterating through all subviews of the scrollview.

Answer 3

You should remove all the UIImageView within the scrollView.

something like

NSArray* subviews = [[scrollview subviews] copy];
for (UIView* v in subviews) {
    [v removeFromSuperview];
}
[subviews release];