Persistent allocation of Heap Memory NSTimer - ios

Question

I discovered an issue with my sample project. I simply create a scheduledTimer that "animate" a label and then, when I reached the result I want, I invalidate the timer and I set an another one, this time as a "clock".
This is the code I use
//
// ViewController.m
//
//
//
//
//
#import "ViewController.h"
#define ANIMATION_INTERVAL 0.07 // in secondi
#define ANIMATION_DURATION 1 // in secondi
#interface ViewController ()
{
int contatore;
NSString *hour;
NSString *minute;
NSString *second;
}
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
contatore = 0;
[self startTimeAnimation];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(void)startTimeAnimation
{
NSTimer * animationTimer = [NSTimer scheduledTimerWithTimeInterval:ANIMATION_INTERVAL target:self selector:#selector(timeout:) userInfo:nil repeats:YES];
}
-(void)timeout: (NSTimer *)timer
{
// Simulate of the Timer Duration with a counter
if (contatore < ceilf(ANIMATION_DURATION/ANIMATION_INTERVAL))
{
// Proceed with animation
contatore++;
int tempHour = arc4random_uniform(24);
int tempMinute = arc4random_uniform(60);
int tempSecond = arc4random_uniform(60);
if (tempHour < 10)
{
hour = [NSString stringWithFormat:#"0%d", tempHour];
}
else
{
hour = [NSString stringWithFormat:#"%d", tempHour];
}
if (tempMinute < 10)
{
minute = [NSString stringWithFormat:#"0%d", tempMinute];
}
else
{
minute = [NSString stringWithFormat:#"%d", tempMinute];
}
if (tempSecond < 10)
{
second = [NSString stringWithFormat:#"0%d", tempSecond];
}
else
{
second = [NSString stringWithFormat:#"%d", tempSecond];
}
_orarioLbl.text = [NSString stringWithFormat:#"%#:%#:%#", hour, minute, second];
}
else
{
// Stops animation
[timer invalidate];
[timer release];
contatore = 0;
[self setActualTime];
// Starts clock
NSTimer *clockTimer = [NSTimer timerWithTimeInterval:.5f target:self selector:#selector(updateClock) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:clockTimer forMode:NSRunLoopCommonModes];
}
}
-(void)updateClock
{
[self setActualTime];
}
-(void)setActualTime
{
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"HH"];
hour = [dateFormatter stringFromDate:[NSDate date]];
[dateFormatter setDateFormat:#"mm"];
minute = [dateFormatter stringFromDate:[NSDate date]];
[dateFormatter setDateFormat:#"ss"];
second = [dateFormatter stringFromDate:[NSDate date]];
_orarioLbl.text = [NSString stringWithFormat:#"%#:%#:%#", hour, minute, second];
[dateFormatter release];
}
#end
Since I start the "clock", memory still stays on 19/20 MB with constant persistent allocation. When the timer updates the minute value, persistent allocations increase as you can see in the gif! How is it possible? However, also 19MB of memory is too much for a simple clock, isn't it?
Profiling on Instruments, the new allocations are all about CoreGraphics!
EDIT I tested it on another device and the persistent allocations decreased. I don't know why, but I solved in this way. Thanks

Answer 1

NSTimer retains its target and that may lead to a retain cycle. Grab a weak reference to self and set that as the target:
__weak typeof(self) weakSelf = self;
NSTimer * animationTimer = [NSTimer scheduledTimerWithTimeInterval:ANIMATION_INTERVAL target:weakSelf selector:#selector(timeout:) userInfo:nil repeats:YES];
and
__weak typeof(self) weakSelf = self;
NSTimer *clockTimer = [NSTimer timerWithTimeInterval:.5f target:weakSelf selector:#selector(updateClock) userInfo:nil repeats:YES];
May I also recommend you create a property for the dateFormatter, as NSDateFormatters are expensive to create. And why are you releasing the dateFormatter? Are you not using ARC?