NSTimer as a self-targeting ivar.
- by Matt Wilding
I have come across an awkward situation where I would like to have a class with an NSTimer instance variable that repeatedly calls a method of the class as long as the class is alive. For illustration purposes, it might look like this:
// .h
@interface MyClock : NSObject {
NSTimer* _myTimer;
}
- (void)timerTick;
@end
-
// .m
@implementation MyClock
- (id)init {
self = [super init];
if (self) {
_myTimer = [[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(timerTick) userInfo:nil repeats:NO] retain];
}
return self;
}
- (void)dealloc {
[_myTimer invalidate];
[_myTImer release];
[super dealloc];
}
- (void)timerTick {
// Do something fantastic.
}
@end
That's what I want. I don't want to to have to expose an interface on my class to start and stop the internal timer, I just want it to run while the class exists. Seems simple enough.
But the problem is that NSTimer retains its target. That means that as long as that timer is active, it is keeping the class from being dealloc'd by normal memory management methods because the timer has retained it. Manually adjusting the retain count is out of the question. This behavior of NSTimer seems like it would make it difficult to ever have a repeating timer as an ivar, because I can't think of a time when an ivar should retain its owning class.
This leaves me with the unpleasant duty of coming up with some method of providing an interface on MyClock that allows users of the class to control when the timer is started and stopped. Besides adding unneeded complexity, this is annoying because having one owner of an instance of the class invalidate the timer could step on the toes of another owner who is counting on it to keep running. I could implement my own pseudo-retain-count-system for keeping the timer running but, ...seriously? This is way to much work for such a simple concept.
Any solution I can think of feels hacky. I ended up writing a wrapper for NSTimer that behaves exactly like a normal NSTimer, but doesn't retain its target. I don't like it, and I would appreciate any insight.
