Question

I have successfully created a UITableView/UITableViewCell that is able to slide up and down and adjusting the height to show options. To see what this means, I have created a video here. The code is as follows:

- (void)swipe:(UISwipeGestureRecognizer *)recognizer direction:(UISwipeGestureRecognizerDirection)direction
{
    if (recognizer && recognizer.state == UIGestureRecognizerStateEnded)
    {
        // Get the table view cell where the swipe occured
        CGPoint location = [recognizer locationInView:self.tableView];
        NSIndexPath* indexPath = [self.tableView indexPathForRowAtPoint:location];
        MyCell* cell = (MyCell *) [self.tableView cellForRowAtIndexPath:indexPath];

        [self.tableView beginUpdates];

        //removing the options view at the other cell before adding a new one

        if (global != nil && global.row != indexPath.row){
            [sideSwipeView removeFromSuperview];
            sideSwipeView = nil;
        }

        //options already exist, we need to remove it
        if (sideSwipeView != nil){
            [sideSwipeView removeFromSuperview];
            sideSwipeView = nil;
            slide = NO;
        } else {
            //options do not exist and therefore we need to add it
            NSArray * buttonData = [[NSArray arrayWithObjects:
                                     [NSDictionary dictionaryWithObjectsAndKeys:@"Mark Read", @"title", @"mark.png", @"image", nil],
                                     [NSDictionary dictionaryWithObjectsAndKeys:@"Track", @"title", @"play.png", @"image", nil],
                                     nil] retain];

            NSMutableArray * buttons = [[NSMutableArray alloc] initWithCapacity:buttonData.count];
            sideSwipeView = [[UIView alloc] initWithFrame:CGRectMake(0, cell.frame.size.height-25, 320, 25)];
            [sideSwipeView setAutoresizingMask:UIViewAutoresizingFlexibleTopMargin];
            [sideSwipeView setBackgroundColor:[UIColor colorWithPatternImage: [UIImage imageNamed:@"dotted-pattern.png"]]];
            [sideSwipeView setTag:-10];

            CGFloat leftEdge = BUTTON_LEFT_MARGIN;
            for (NSDictionary* buttonInfo in buttonData)
            {
                if (!([[buttonInfo objectForKey:@"title"] isEqualToString:@"Mark Read"] && [[[topics objectAtIndex:indexPath.row] unread] intValue] == 0))
                {

                    UIButton* button = [UIButton buttonWithType:UIButtonTypeCustom];

                    button.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleTopMargin;

                    UIImage* buttonImage = [UIImage imageNamed:[buttonInfo objectForKey:@"image"]];
                    if ([[topics objectAtIndex:indexPath.row] tracked] && [[buttonInfo objectForKey:@"title"] isEqualToString:@"Track"]){
                        buttonImage = [UIImage imageNamed:@"pause.png"];
                        [button setSelected:YES];
                    } else {
                        [button setSelected:NO];
                    }
                    button.frame = CGRectMake(leftEdge, 0, buttonImage.size.width, buttonImage.size.height);

                    UIImage* grayImage = [self imageFilledWith:[UIColor colorWithWhite:0.9 alpha:1.0] using:buttonImage];
                    [button setImage:grayImage forState:UIControlStateNormal];

                    if ([[buttonInfo objectForKey:@"title"] isEqualToString:@"Mark Read"]){
                        [button addTarget:self action:@selector(markRead:) forControlEvents:UIControlEventTouchUpInside];
                    } else if ([[buttonInfo objectForKey:@"title"] isEqualToString:@"Track"]){
                        [button addTarget:self action:@selector(track:) forControlEvents:UIControlEventTouchUpInside];
                    }
                    [button setTag:indexPath.row];
                    [buttons addObject:button];

                    [sideSwipeView addSubview:button];

                    leftEdge = leftEdge + buttonImage.size.width + BUTTON_SPACING;
                }
            }

            [cell.contentView addSubview:sideSwipeView];
            [sideSwipeView release];
            global = indexPath;
            slide = YES;

        }
        [self.tableView endUpdates]; 
        [self.tableView deselectRowAtIndexPath:indexPath animated:YES];        

    }
}

However, I am not confident that the code is memory correct (i.e: ther’s no memory leak and I am not misusing anything). I am mostly not confident in the sideSwipeView alloc, dealloc, and setting it up to nil. I think the others are fine. Can someone give me any pointers?

Profiler result:

Answer 1

The rule of thumb when dealing with memory management in Objective-C is that you should explicitly release objects that you are: (1) allocating (alloc), (2) cloning (copy), or newing up (new, which is a combination of alloc/init).

With that knowledge, go over your code, look for places where you’re doing the above, and make sure you’re releasing them once you’re done with them. One example of an object that you’re not releasing is buttons.

You should also read up on how objects are retained. For example, when you remove a view from a superview, if it is not retained anywhere else, it’ll be released. You don’t need to explicitly set the value to nil.