How to deal with leaks in iOS when memory consumpt

Question

I am working on an iOS ARC app (more code available on request), and earlier I was producing and discarding large numbers of images. I thought that I somewhere still had a reference to images, even if I called removeFromSuperview and tried to remove all references to no-longer-used images. I tried Leaks, and Leaks reported roughly linear increase in memory usage over time, starting around 17M.

I went through and replaced all references to images to be instance variables, so they would take a small, finite, and fixed amount of memory, and transformed, instead of getting rid of, the images used for clock hands. This, unfortunately, resulted in slowly increasing memory usage over time, starting at 5M rather than 17M, but otherwise the same problem, simply translated to a better starting point.

A trimmed version of my code is below. Could you tell me what is leaky (or "pseudo-leaky" as Leaks did not indicate a leak) about this and how I can stay close to the memory bounds the code uses when it starts up?

Thanks,

- (void) renderScreen
{
int height = floor([[UIScreen mainScreen] bounds].size.height + .4);
int width = floor([[UIScreen mainScreen] bounds].size.width + .4);

if (height == 2048 || height == 2008 || height == 1024 || height == 1004 || height == 984)
{
    if (UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-Portrait.png"];
    }
    else
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-Landscape.png"];
    }
}
else if (height == 1536 || height == 768 || height == 748 || height == 728)
{
    _backgroundImage = [UIImage imageNamed:@"Background-Default-Landscape.png"];
}
else if (height == 1136 || height == 1116 || height == 1096)
{
    if (UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-568.png"];
    }
    else
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-Rotated-568.png"];
    }
}
else if (height == 960 || height == 940 || height == 920 || height == 480 || height == 460 || height == 440)
{
    if (UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default.png"];
    }
    else
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-Rotated.png"];
    }
}
else if ((height == 640 || height == 620 || height == 600) && (width == 1136 || width == 1116 || width == 1096))
{
    _backgroundImage = [UIImage imageNamed:@"Background-Rotated-568.png"];
}
else if ((height == 640 || height == 620 || height == 600 || height == 320 || height == 300 || height == 280) && (width == 960 || width == 940 || width == 920 || width == 480 || width == 470 || width == 410))
{
    if (UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-Portrait.png"];
    }
    else
    {
        _backgroundImage = [UIImage imageNamed:@"Background-Default-Rotated.png"];
    }
}
else
{
    _backgroundImage = [UIImage imageNamed:@"Background-Default-Portrait.png"];

}
if (!UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
{
    int juggle = height;
    height = width;
    width = juggle;
}
NSUInteger centerX = width * .5;
NSUInteger centerY = height * .5;

_containerRect = CGRectZero;
_containerRect.size = [[UIScreen mainScreen] bounds].size;

self.view.backgroundColor = [UIColor colorWithPatternImage:_backgroundImage];
_backgroundView = [[UIImageView alloc] initWithImage:_backgroundImage];
[self.view addSubview:_backgroundView];
if (_changed)
{
    _containerView = [[UIView alloc] initWithFrame:_containerRect];
}

double timeStampSeconds = [[NSDate date] timeIntervalSince1970];
double hours   = fmod(timeStampSeconds / 86400, 24);
double minutes = fmod(timeStampSeconds /  3600, 60);
double seconds = fmod(timeStampSeconds,     60);
NSLog(@"Milliseconds: %lf, Hours: %.0f, minutes: %.0f, seconds: %.0f", timeStampSeconds * 1000.0, hours, minutes, seconds);
[_containerView removeFromSuperview];
_containerView = [[UIView alloc] initWithFrame:_containerRect];
_hourHandImage = [UIImage imageNamed:@"hour-hand.png"];
_hourHandView = [[UIImageView alloc] initWithImage:_hourHandImage];
_hourHandImage = [UIImage imageNamed:@"hour-hand.png"];
_hourHandView = [[UIImageView alloc] initWithImage:_hourHandImage];
[self.view addSubview:_hourHandView];

_hourHandView.layer.anchorPoint = CGPointMake(0.5f, 0.5f);
_hourTransform = CGAffineTransformMakeTranslation(centerX, centerY);
_hourTransform = CGAffineTransformTranslate(_hourTransform, -17, -127);
_hourTransform = CGAffineTransformRotate(_hourTransform, hours / 12.0 * M_PI * 2.0);
_minuteTransform = CGAffineTransformMakeTranslation(centerX, centerY);
_minuteTransform = CGAffineTransformTranslate(_minuteTransform, -10, -182);
_minuteTransform = CGAffineTransformRotate(_minuteTransform, minutes / 60.0 * M_PI * 2.0);
_hourHandView.transform = _hourTransform;
_minuteHandImage = [UIImage imageNamed:@"minute-hand.png"];
_minuteHandView = [[UIImageView alloc] initWithImage:_minuteHandImage];
_minuteHandView.transform = _minuteTransform;
[self.view addSubview:_minuteHandView];
_minuteTransform = CGAffineTransformRotate(_minuteTransform, minutes / 60.0 * M_PI * 2.0);
_secondHandImage = [UIImage imageNamed:@"second-hand.png"];
_secondTransform = CGAffineTransformMakeTranslation(centerX, centerY);
_secondTransform = CGAffineTransformTranslate(_secondTransform, -10, -189);
_secondTransform = CGAffineTransformRotate(_secondTransform, seconds / 60.0 * M_PI * 2.0);
_secondHandView = [[UIImageView alloc] initWithImage:_secondHandImage];
_secondHandView.transform = _secondTransform;
[self.view addSubview:_secondHandView];
}

--EDIT--

I have refactored the one method into two methods, one for initial display, and one for incremental updates. It appears that the incremental update method is only called once, as the clock is frozen and the signature logging statement is called exactly once.

I now have, for the update portion:

- (void)render
{
    [self renderScreenInitial];
    [NSTimer scheduledTimerWithTimeInterval:0.002
                                     target:self
                                   selector:@selector(renderingTimer:)
                                   userInfo:nil
                                    repeats:YES];
}

- (void) renderScreenIncremental
{
    int height = floor([[UIScreen mainScreen] bounds].size.height + .4);
    int width = floor([[UIScreen mainScreen] bounds].size.width + .4);
    if (!UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
    {
        int juggle = height;
        height = width;
        width = juggle;
    }
    double decibelAngle = M_PI / 4 + (_decibel / 60) * M_PI / 2;
    double decibelAngleDifference = decibelAngle - _previousDecibelAngle;
    _previousDecibelAngle = decibelAngle;
    NSLog(@"%lf %lf", _decibel, decibelAngle);
    _decibelNeedleView = [[UIImageView alloc] initWithImage:_decibelNeedle];
    // CGAffineTransform decibelTransform = CGAffineTransformMakeTranslation(centerX, centerY);
    CGAffineTransform decibelTransform = CGAffineTransformMakeRotation(decibelAngleDifference);
    decibelTransform = CGAffineTransformTranslate(decibelTransform, sin(decibelAngle - .06) * -298, -cos(decibelAngle - .06) * 298);
    _decibelNeedleView.transform = decibelTransform;
    [self.view addSubview:_decibelNeedleView];
    double timestampSeconds = [[NSDate date] timeIntervalSince1970];
    double timestampSecondsDifference = timestampSeconds - _previousTimestampSeconds;
    _previousTimestampSeconds = timestampSeconds;
    double hoursDifference   = fmod(timestampSecondsDifference / 86400, 24);
    double minutesDifference = fmod(timestampSecondsDifference /  3600, 60);
    double secondsDifference = fmod(timestampSecondsDifference,     60);
    NSLog(@"Milliseconds: %lf, Hours: %.0f, minutes: %.0f, seconds: %.0f", timestampSecondsDifference * 1000.0, hoursDifference, minutesDifference, secondsDifference);
    _hourHandView.transform = CGAffineTransformMakeRotation(hoursDifference);
    _minuteHandView.transform = CGAffineTransformMakeRotation(minutesDifference);
    _secondHandView.transform = CGAffineTransformMakeRotation(secondsDifference);
}

-(void)renderingTimer:(NSTimer *)timer {
    [self renderScreenIncremental];
}

I appreciate the help. Do you see why it should update the display once and then not continue to keep it updated?

Thanks,

Answer 1

The gradual increase in memory using the APIs you are using is expected behavior. [UIImage imageNamed:] will cache the image. If you're wanting to test whether these get released when the cache is flushed, cause a memory warning to occur. You can do this in the simulator by going to Hardware menu and select Simulate Memory Warning.

You can also do this on-device programatically with the following code:

[[NSNotificationCenter defaultCenter] postNotificationName:UIApplicationDidReceiveMemoryWarningNotification 
                                                    object:[UIApplication sharedApplication]];

YOU SHOULD NOT SHIP A PRODUCTION APP WITH THIS CODE

Answer 2

First and foremost, you should use Allocations tool in Instruments to identify what's being allocated and not being released. I'd suggest you want WWDC 2012 video iOS App Performance: Memory, which demonstrates this, amongst other things.

Using Instrument's Allocations tool, you won't be guessing what's being allocated and not being released, but rather you can use heapshots/generations to identify the actual objects that are being allocated and not being released within some time range of your picking. You can even drill in and see where the offending objects were originally allocated.

With that aside, glancing at your code, it appears that you're removing and re-adding the container, but nothing is going into the container. And you're adding the hour/minute/second hands, but never removing them. Perhaps you meant to add those to the container?

Also, your code doesn't describe what _changed does, but if that's YES, then you're effectively creating a _containerView, removing it from its superview (even though it was never added to a superview), and then discarding it and creating another _containerView. Very strange.

I'm also inferring from this code that you'll be calling renderScreen many times. If that's true, then I might suggest separating the "creation" of the view stuff (adding background, the various images, etc.) from the "change" of the view (the adjustment of the transform values). If possible, you should add your views once, and then do the bare minimum (changing the transforms) upon updates.