How to manage memory effectivily in ios - ios

Question

I have created a view in which background is changing randomly.A total of 10 images .that i am using for displaying .
Below is the code for Background images.
- (void)viewWillAppear:(BOOL)animated
{
myTimer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:#selector(changeImage) userInfo:nil repeats:YES];
}
-(void)changeImage
{
self.imgView.image=nil;
int randNum = rand() % (9 - 1) + 1;.
NSString *num = [NSString stringWithFormat:#"%d", randNum];
self.imgView.image=[UIImage imageNamed:[NSString stringWithFormat:#"%#.png",num]];
}
Code is working fine .
My question is;its showing over 34mb memory usage ,when i push other view it's still over 34 mb.although i have make the myTimer variable nil;
- (void)viewWillDisappear:(BOOL)animated
{
[myTimer invalidate];
self.imgView.image=nil;
myTimer = Nil;
}
How can i manage memory usage here?

Answer 1

You have to invalidate your timer, setting it to nil will not prevent it from firing:
Once scheduled on a run loop, the timer fires at the specified interval until it is invalidated. A non-repeating timer invalidates itself immediately after it fires. However, for a repeating timer, you must invalidate the timer object yourself by calling its invalidate method. Calling this method requests the removal of the timer from the current run loop; as a result, you should always call the invalidate method from the same thread on which the timer was installed. Invalidating the timer immediately disables it so that it no longer affects the run loop. The run loop then removes the timer (and the strong reference it had to the timer), either just before the invalidate method returns or at some later point. Once invalidated, timer objects cannot be reused.
So you need
[myTimer invalidate];
myTimer = nil;
To stop it running.
In terms of the memory use; what are you expecting to happen? If you've just pushed a new view on the navigation stack the old view is still around and its contents will be in memory. The layer cache won't be removed until the app comes under memory pressure, and 34MB probably isn't going to cause that.
As pointed out in comments, imageNamed caches images in memory (again, until you come under memory pressure) and you also need to call the super implementations of viewXXappear to make sure UIKit is handling things properly.
Try simulating a memory warning and seeing what happens. I don't think you've got anything to worry about, now you're invalidating the timer.

Answer 2

Also try adding to viewdiddisappear,
self.imgView=nil;

Answer 3

The method imageNamed: caches the image it only evict it during memory pressure situations, try to use imageWithContentsOfFile: and when you want to force a release set the image property of the image view to nil.