Question

I have a UIViewController thats presented modally. When I watch the memory allocations Instrument, the memory usage increases when the view is presented, but when it’s exited the memory isn’t released.
If I keep opening and closing the view, the memory just keeps getting higher.
Instruments doesn’t report a memory leak!
What could be causing this? The View Controller code is below (I’ve skipped the didSelectRow code).
Dealloc is always called.

EDIT – I am using ARC

.h

#import <UIKit/UIKit.h>
@class OutlineTextUILabel;

@interface StoreViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> {

    int starCount;
    NSMutableArray *_singleUseArray;
    NSMutableArray *_fullUseArray;

}

@property (weak, nonatomic) IBOutlet UITableView *tableView;
@property (weak, nonatomic) IBOutlet OutlineTextUILabel *starCountLbl;
- (IBAction)exitBtnPressed:(id)sender;

.m

#import "StoreViewController.h"
#import "NSUserDefaults+MPSecureUserDefaults.h"
#import "PowerUpCell.h"
#import "OutlineTextUILabel.h"
#import "PowerUpSingleton.h"
#import "PowerUp.h"

#define kPrefsNumberOfStars             @"numberOfStars"

@interface StoreViewController ()

@end

@implementation StoreViewController
@synthesize tableView = _tableView;
@synthesize starCountLbl;

#pragma mark View Methods

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Display star count
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    BOOL valid = NO;
    starCount = [prefs secureIntegerForKey:kPrefsNumberOfStars valid:&valid];
    if (!valid) {
        NSLog(@"Stars Tampered With!");
        self.starCountLbl.text = @"Err";
    } else {
        self.starCountLbl.text = [NSString stringWithFormat:@"%d",starCount];
    }

    // Tableview setup
    CGRect frame2 = CGRectMake(0, 0, 320, 40);
    UIView *footer = [[UIView alloc] initWithFrame:frame2];
    footer.backgroundColor = [UIColor clearColor];
    self.tableView.tableFooterView = footer;
    self.tableView.opaque = NO;
    self.tableView.backgroundView = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:YES];

    if (![[PowerUpSingleton sharedList] refreshArray]) {
        NSLog(@"Error, %s",__FUNCTION__);
    } else {
        [self performSelectorOnMainThread:@selector(workOutSingleUseToDisplay) withObject:nil waitUntilDone:YES];
        [self performSelectorOnMainThread:@selector(workOutFullUseToDisplay) withObject:nil waitUntilDone:YES];
        [self.tableView reloadData];
    }
}

- (void)workOutSingleUseToDisplay
{
    _singleUseArray = [[NSMutableArray alloc] init];
    for (PowerUp *pu in [[PowerUpSingleton sharedList] sharedArray]) {
        if (!pu.fullUnlock) {
            [_singleUseArray addObject:pu];
        }
    }
}

- (void)workOutFullUseToDisplay
{
    _fullUseArray = [[NSMutableArray alloc] init];
    for (PowerUp *pu in [[PowerUpSingleton sharedList] sharedArray]) {
        if (pu.prefFullName != nil) {
            [_fullUseArray addObject:pu];
        }
    }

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

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

- (void)viewDidUnload {
    [self setTableView:nil];
    [self setStarCountLbl:nil];
    [super viewDidUnload];
}

#pragma mark TableView Setup Methods

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 2;
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    if (section == 0) {
        return @"Single Use";
    } else if (section == 1) {
        return @"Use forever";
    }

    return nil;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if (section == 0) {
        return [_singleUseArray count];
    } else if (section == 1) {
        return [_fullUseArray count];
    }

    return 0;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *cellIdentifier;
    if (indexPath.section == 0) {
        cellIdentifier = @"powerUpCellSingleUse";
    } else if (indexPath.section == 1) {
        cellIdentifier = @"powerUpCell";
    }

    PowerUpCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (cell == nil) {
        cell = [[PowerUpCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
    }

    if (indexPath.section == 0) {
        PowerUp *tmpPU = [_singleUseArray objectAtIndex:indexPath.row];
        cell.descriptionLbl.text = tmpPU.displayName;
        int cost = tmpPU.costSingle;
        cell.costLbl.text = [NSString stringWithFormat:@"%d",cost];
        if (cost > starCount) {
            cell.costLbl.textColor = [UIColor redColor];
        } else {
            cell.costLbl.textColor = [UIColor blueColor];
        }
        int howMany = tmpPU.numberOwned;
        cell.howManyLbl.text = [NSString stringWithFormat:@"%d",howMany];

    } else if (indexPath.section == 1) {
        PowerUp *tmpPU = [_fullUseArray objectAtIndex:indexPath.row];
        cell.descriptionLbl.text = tmpPU.displayName;
        int cost = tmpPU.costFull;
        cell.costLbl.text = [NSString stringWithFormat:@"%d",cost];
        if (cost > starCount) {
            cell.costLbl.textColor = [UIColor redColor];
        } else {
            cell.costLbl.textColor = [UIColor blueColor];
        }
        if (tmpPU.fullUnlock) {
            cell.costLbl.textColor = [UIColor greenColor];
            cell.costLbl.text = @"---";
        }
    }

    return cell;
}

#pragma mark -

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

- (void)dealloc
{
    NSLog(@"%s",__FUNCTION__);
    self.tableView = nil;
    self.starCountLbl = nil;
}

@end

EDIT ————-
Something seems not to be right. I’ve added an NSLog to the cell alloc, and it’s never called, even though the cells are created!

PowerUpCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (cell == nil) {
        NSLog(@"new cell");
        cell = [[PowerUpCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
    }

EDIT July 1st ——
I’ve added a Navigation controller and now use push instead of modal and this problem is still here.
I’ve taken heap shots with Instruments by moving back and forward between views a few times and it seems maybe the cells are still hanging around, as this screenshot shows gesture recogniser still around from a previous load of the view.

Answer 1

It is because you used your IBOutlets as weak, instead of using strong.

I actually believe this is a flaw in the XCode environment, as it should warn you of this kind of behavior.

As a best practice, I would suggest letting XCode generate the IBOutlets by dragging the views to the code in the Interface Builder, to avoid such annoying pitfalls.