Question about NSTimer and retain

Question

This code works well

@property (nonatomic, retain) NSTimer *timer;
self.timer = [[NSTimer timerWithTimeInterval:kAdsAppearTimeInterval target:self selector:@         


        

Answer 1

Not a lot to go on... but:

@property (nonatomic, retain) NSTimer *timer;
self.timer = [[NSTimer timerWithTimeInterval:kAdsAppearTimeInterval target:self selector:@selector(timerFired:) userInfo:nil repeats:NO] retain];

That'll end up retaining the timer 3 times and self once.

1. Timer +1 for -retain
2. Timer +1 for scheduling it

3. Timer +1 for the property assignment

4. self +1 for being the target of the timer

The timer will be released once when fired (because it'll be unscheduled from the run loop). self will be released when the timer is invalidated or released (you shouldn't have to care).

So, you have two retain counts to account for. The call to retain in the code above is noise; don't bother as the property assignment will retain it.

That leaves the property's retain. The most obvious way is to release the timer in -dealloc.

However, unless you need to potentially invalidate the timer before it fires, there is no reason to have an instance variable referring to the timer at all. Even if you do have an iVar, there is no reason to retain the timer either as long as you set self.timer = nil in your timerFired: method (and set it to nil if you invalidate anywhere).