How to update view from custom Timer object - ios

Question

I'm building an app with a timer in it, and I've created a custom class, Timer, which is a wrapper around the NSTimer class. It has a property called remainingTime which is periodically updated as the timer is running.
My view controller, TimerVC, instantiates a Timer object, and needs to update its view based on timer.remainingTime. How do I achieve this?
I believe I should be using a delegate here, but I don't know how it would work. Which class should implement the delegate method?
Or maybe my approach is all wrong?
Edit: The reason I'm not using NSTimer inside of TimerVC is because I want to abstract it for re-use, and also decouple it from the view.
Here is my code for my Timer class:
#import "Timer.h"
#define SECONDS_INTERVAL 1
#interface Timer()
#property (strong, nonatomic) NSTimer *timer;
#property NSInteger seconds;
#property NSInteger secondsRemaining;
#end
#implementation Timer
- (Timer *)initWithSeconds:(NSInteger)seconds {
self = [super init];
if (self) {
self.seconds = seconds;
self.secondsRemaining = self.seconds;
}
return self;
}
- (void)start {
self.timer = [NSTimer timerWithTimeInterval:SECONDS_INTERVAL target:self selector:#selector(updateSecondsRemaining) userInfo:nil repeats:YES];
}
- (void)pause {
}
- (void)stop {
[self.timer invalidate];
self.timer = nil;
}
- (void)reset {
[self stop];
self.secondsRemaining = self.seconds;
}
- (void)updateSecondsRemaining {
self.secondsRemaining = self.secondsRemaining - SECONDS_INTERVAL;
if (self.secondsRemaining == 0) {
[self timerFinished];
}
}
- (void)timerFinished {
[self reset];
}

Answer 1

Typically your view's view controller would implment that delegate.
Define the protocol in a .h file. Let's say its name is CustomTimerDelegate. Add an id <CustomTimerDelegate> timerDelegate; property to your custom timer. Set the delegate when the custom timer was created. The protocol contains one method at least that is invoked by the timer every time when the view controller should update its view. The view conroller implements the protocol. In its .h file you add <CustomTimerDelegate> to the #interface statement. In its .m file you implement the method that is called though the protocol.
Does that answer your question?

Answer 2

I don't see why you would need to write a custom timer for that.
In your TimerVC use this to create a new timer:
[NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(timerCallback:)
userInfo:nil
repeats:YES];
This will call the timerCallback: method every second. In this method you can update your remaining time property and you can also update your view.

Answer 3

Just completing Hermann Klecker answer.. please don't forget that on your timer class the property should be
#property(nonatomic, weak) id <CustomTimerDelegate> delegate
This is.. a weak property to avoid memory leaks when having your VC holding the timer strongly and your timer holding the delegate (in this case the VC) strongly... they would be retained in memory even if VC gets dumped (because timer would have a strong pointer to it) causing VC to not deallocate, thus not making the Timer deallocate thus not making the VC deallocate... and so forth...
with weak you avoid this...