UITableView crashes on scroll (memory warnings)

Question

I have made my first UITableView, but when the number of cells is higher than what can be shown on the screen, and I scroll, it then crashes because of lack of memory.

I implemented the SDWEBIMAGE library to load the pictures async. and cache the images afterwards.

If more code is needed, please let me know !

I am a complete newbie at this, so please be gentle :)

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *myIdentifier = @"defaultcell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:myIdentifier forIndexPath:indexPath];

    if(cell == nil){
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:myIdentifier];

    }

    UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle: UIActivityIndicatorViewStyleWhiteLarge];
    spinner.center = CGPointMake(160, 47);
    [spinner startAnimating];
    [cell.contentView addSubview:spinner];

    //hide labels until done loading
    cell.textLabel.hidden = YES;
    cell.detailTextLabel.hidden = YES;
    cell.imageView.hidden = YES;

    UIImageView *iv = [[UIImageView alloc] initWithFrame:(CGRect){.size={80, 60}}];
    iv.contentMode = UIViewContentModeScaleAspectFill;
    iv.clipsToBounds = YES;
    iv.frame = CGRectMake(15, 17, 80, 60);

    NSString *profilePicName = [NSString stringWithFormat:@"%@%@", [self.dbhandler getPicturesPath], [[gallery objectAtIndex:indexPath.row] valueForKey: @"filename"]];

    [iv setImageWithURL:[NSURL URLWithString:profilePicName]  placeholderImage:[UIImage imageNamed:@"placeholder.png"] completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType){
            [spinner stopAnimating];
            cell.textLabel.hidden = NO;
            cell.detailTextLabel.hidden = NO;
            cell.imageView.hidden = NO;

            [cell.contentView addSubview:iv];
        }];

    NSString *subtitle = [NSString stringWithFormat:@"Comments:  %@ \nPosted:        %@", [[gallery objectAtIndex:indexPath.row] valueForKey:@"comments"], [[gallery objectAtIndex:indexPath.row] valueForKey:@"created_at"]];

    cell.detailTextLabel.numberOfLines = 0;
    cell.textLabel.text = [NSString stringWithFormat:@"Votes:    %@",[[gallery objectAtIndex:indexPath.row] valueForKey:@"votes"]];
    cell.detailTextLabel.text = subtitle;

    return cell;
}

UPDATED FUNCTION:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *myIdentifier = @"defaultcell";
    UIActivityIndicatorView *spinner;
    UIImageView *iv;

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:myIdentifier forIndexPath:indexPath];

    if(cell == nil){
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:myIdentifier];
        //build spinner
        spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle: UIActivityIndicatorViewStyleWhiteLarge];
        spinner.center = CGPointMake(160, 47);
        spinner.tag = 101;
        [cell.contentView addSubview:spinner];

        //build ImageView
        iv = [[UIImageView alloc] initWithFrame:(CGRect){.size={80, 60}}];
        iv.contentMode = UIViewContentModeScaleAspectFill;
        iv.clipsToBounds = YES;
        iv.tag = 102;
        iv.frame = CGRectMake(15, 17, 80, 60);
        [cell.contentView addSubview:iv];
    } else {
        spinner = (UIActivityIndicatorView*)[cell viewWithTag:101];
        iv = (UIImageView*)[cell viewWithTag:102];
    }



    [spinner startAnimating];
    //the rest goes here


    cell.textLabel.hidden = YES;
    cell.detailTextLabel.hidden = YES;
    cell.imageView.hidden = YES;

    NSString *profilePicName = [NSString stringWithFormat:@"%@%@", [self.dbhandler getPicturesPath], [[gallery objectAtIndex:indexPath.row] valueForKey: @"filename"]];
    NSLog(@"%@", profilePicName);

    [iv setImageWithURL:[NSURL URLWithString:profilePicName]  placeholderImage:[UIImage imageNamed:@"placeholder.png"] completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType){
        [spinner stopAnimating];
        cell.textLabel.hidden = NO;
        cell.detailTextLabel.hidden = NO;
        cell.imageView.hidden = NO;

        NSLog(@"done");
        [cell.contentView addSubview:(UIImageView *)[cell viewWithTag:102]];
    }];


    NSString *subtitle = [NSString stringWithFormat:@"Comments:  %@ \nPosted:        %@", [[gallery objectAtIndex:indexPath.row] valueForKey:@"comments"], [[gallery objectAtIndex:indexPath.row] valueForKey:@"created_at"]];

    cell.detailTextLabel.numberOfLines = 0;
    cell.textLabel.text = [NSString stringWithFormat:@"Votes:    %@",[[gallery objectAtIndex:indexPath.row] valueForKey:@"votes"]];
    cell.detailTextLabel.text = subtitle;

    return cell;
}

Answer 1

Every-time you reuse a cell you are adding the UIActivityIndicatorView/spinner and UIImageView/iv as subviews. Better approach is to use a custom Prototype cell in the storyboard or reuse existing views by setting a Tag.

UIActivityIndicatorView *spinner;
UIImageView *iv;

if(cell == nil){
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:myIdentifier];
    //build spinner
    spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle: UIActivityIndicatorViewStyleWhiteLarge];
    spinner.center = CGPointMake(160, 47);
    spinner.tag = 101;
    [cell.contentView addSubview:spinner];

    //build ImageView
    iv = [[UIImageView alloc] initWithFrame:(CGRect){.size={80, 60}}];
    iv.contentMode = UIViewContentModeScaleAspectFill;
    iv.clipsToBounds = YES;
    iv.tag = 102;
    iv.frame = CGRectMake(15, 17, 80, 60);
    [cell.contentView addSubview:iv];
} else {
    spinner = (UIActivityIndicatorView*)[cell.contentView viewWithTag:101];
    iv = (UIImageView*)[cell.contentView viewWithTag:102];
}

[spinner startAnimating];
//the rest goes here

You need to remove other addSubView calls(specifically in the callback block).

This should help you to get started.