How to know when to invalidate an `NSTimer`

Question

Here\'s my issue:

I have a model class that has an NSTimer in it that I want the Timer to run for the entire lifespan of the model object. Initiliazati

Answer 1

Based on @Martin R idea, I create custom class which easier to use, and add some checking to avoid crash.

@interface EATimerTarget : NSObject

// Initialize with block to avoid missing call back
- (instancetype)initWithRealTarget:(id)realTarget timerBlock:(void(^)(NSTimer *))block;

// For NSTimer @selector() parameter
- (void)timerFired:(NSTimer *)timer;

@end

@interface EATimerTarget ()
@property (weak, nonatomic) id realTarget;
@property (nonatomic, copy) void (^timerBlock)(NSTimer *); // use 'copy' to avoid retain counting
@end

@implementation EATimerTarget

- (instancetype)initWithRealTarget:(id)realTarget timerBlock:(void (^)(NSTimer *))block {
    self = [super init];
    if (self) {
        self.realTarget = realTarget;
        self.timerBlock = block;
    }
    return self;
}

- (void)timerFired:(NSTimer *)timer {
    // Avoid memory leak, timer still run while our real target is dealloc
    if (self.realTarget) {
        self.timerBlock(timer);
    }
    else {
        [timer invalidate];
    }
}

@end

Here is my sample class

@interface MyClass
@property (nonatomic, strong) NSTimer *timer;
@end

@implementation MyClass

- (id)init
{
    self = [super init];
    if (self) {
         // Using __weak for avoiding retain cycles
         __weak typeof(self) wSelf = self;
    EATimerTarget *timerTarget = [[EATimerTarget alloc] initWithRealTarget:self timerBlock: ^(NSTimer *timer) {
        [wSelf onTimerTick:timer];
    }];
         self.timer = [NSTimer timerWithTimeInterval:1 target:timerTarget selector:@selector(timerFired:) userInfo:nil repeats:YES];
         [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
    }
    return self;
}

- (void)dealloc
{
    [self.timer invalidate]; // This releases the EATimerTarget as well! 
    NSLog(@"### MyClass dealloc");
}

- (void)onTimerTick:(NSTimer *)timer {
     // DO YOUR STUFF!
     NSLog(@"### TIMER TICK");
}

@end