Question

I’m programming my first iOS application and I’m trying to asynchronously load images into my UITableViewCells. I’m loading the images in the background into a NSMutableArray, which is then retrieved at the cellForRowAtIndexPath method. The cells are able to load the images, but crashes on the ~5th cell and gives me one of two different errors:

SIGABRT at the @synthesize line in ApplicationCell.m with malloc: * error for object 0x6c30e60: double free

or just enters gdb and points at iconView.image = newIcon; (Thread 1).

I’ve declared the NSMutableArray *imageArray in the @interface of the table view controller and set it as a @property, then @synthesize’d it:

@synthesize searchArray;
...
- (void)viewDidLoad {
    [super viewDidLoad];
    ...
    self.imageArray = [[NSMutableArray alloc] initWithCapacity:8]; //<-- Am I doing this correctly?
    for (int i=0; i < 8; i++) {
        [self.imageArray addObject:[UIImage imageNamed:@"empty.png"]];
    }
    ...
}

There will be a maximum of 8 images loaded in the background, which will be placed inside imageArray:

- (void)requestFinishedImage:(ASIFormDataRequest*)request {
    //image request
    NSData *responseData = [request responseData];
    NSIndexPath *index = [NSIndexPath indexPathForRow:request.tag inSection:0];
    UIImage *image = [[UIImage alloc] initWithData:responseData];
    NSLog(@"requested Image with tag: %d",request.tag);
    [imageArray replaceObjectAtIndex:request.tag withObject:image];
    ApplicationCell *cell = (ApplicationCell *)[self.tableView cellForRowAtIndexPath:index];
    [cell setIcon2:image];
    cell.icon = image;
    [image release];
}

Here is the cellForRowAtIndexPath:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    ApplicationCell *cell = (ApplicationCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        [self.cellNib instantiateWithOwner:self options:nil];
        cell = tmpCell;
        self.tmpCell = nil;
    }
    UIImage *image;
    NSUInteger row = [indexPath row];

    [cell setItem2: [[searchArray objectAtIndex:row] objectForKey:@"item"]];
    [cell setPrice2: cell.price];
    image = [imageArray objectAtIndex:row];
    NSLog(@"num elements in imageArray = %d, loading: %d",[imageArray count], row);
    [cell setIcon2: image];
[image release];
    return cell;
}

And here are my ApplicationCell.h and ApplicationCell.m

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface ApplicationCell : UITableViewCell
{

    UIImage *icon;
    NSString *item;
    NSString *price;
    IBOutlet UIImageView *iconView;
    IBOutlet UILabel *itemLabel;
    IBOutlet UILabel *priceLabel;
}
- (void)setIcon2:(UIImage *)newIcon;
- (void)setItem2:(NSString *)newItem;
- (void)setPrice2:(NSString *)newPrice;

@property(retain) UIImage *icon;
@property(retain) NSString *item;
@property(retain) NSString *price;

@end

ApplicationCell.m

#import "ApplicationCell.h"

@implementation ApplicationCell

@synthesize icon, item, price;

- (void)setIcon2:(UIImage *)newIcon
{
    [self setIcon:newIcon];
    iconView.opaque = YES;
    iconView.image = newIcon;
}
- (void)setItem2:(NSString *)newItem
{
    [self setItem:newItem];
    itemLabel.text = newItem;
}

- (void)setPrice2:(NSString *)newPrice
{
    [self setPrice:newPrice];
    priceLabel.text = newPrice;
}


- (void)dealloc
{
    [icon release];
    [item release];
    [price release];

    [iconView release];
    [itemLabel release];
    [priceLabel release];

    [super dealloc];
}

@end

There are probably some mistakes in the code since this is my first time trying an iOS application, but please let me know so I can learn! I’ve been stuck on this async loading issue for too long.. Any help is appreciated!

Answer 1

Take out the [image release] call in -tableView:cellForRowAtIndexPath:. You didn’t retain it there,so you don’t need to release it. If you use Xcode’s static analyzer, it should find memory errors like this.