带有NSTimer的UIGestureRecognizer永不消亡

Question

I'm trying to set up a "FastForward/Next" button in a media player that can be tapped to move to the next song or held to fast forward within the current song. Mostly, it works: you can successfully fastforward and successfully move to the next song, but the thing is, the NSTimer that makes it work never invalidates, so once you start fastforwarding, you never stop.

I set up the gesture recognizers in viewDidLoad :

UITapGestureRecognizer *singleTapFastForward = [[UITapGestureRecognizer alloc] initWithTarget: self action:@selector(nextSong:)];
singleTapFastForward.numberOfTapsRequired = 1;
[_buttonNext addGestureRecognizer:singleTapFastForward];

_holdFastForward = [[UILongPressGestureRecognizer alloc] initWithTarget: self action:@selector(startFastForward:)];
[_buttonNext  addGestureRecognizer:_holdFastForward];
[singleTapFastForward requireGestureRecognizerToFail:_holdFastForward];

and here is the meat of the function:

- (IBAction)startFastForward:(id)sender {
    _timerFastForward = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(executeFastForward) userInfo:nil repeats:YES];
}

- (void)executeFastForward {
    [_avPlayer seekToTime:CMTimeMake(CMTimeGetSeconds([_avPlayer currentTime]) + 10, 1)];
    if(_holdFastForward.state == 0) {
        [self endFastForward:self];
    }
}

- (IBAction)endFastForward:(id)sender {
    [_timerFastForward invalidate];
}

Here's the tricky part: when I set a breakpoint at the if(_holdFastForward.state == 0) line, it starts working as soon as I let go of the button (as it should), and it successfully calls the endFastForward method. By my reckoning, that should kill the timer and end the whole cycle, but then executeFastForward gets called again, and then again and again. The invalidate line just seems to do nothing (and there are no other points in my code that call executeFastForward ).

Any ideas? This seems like a simple thing, and if the invalidate line worked everything would be perfect. I just don't know why executeFastForward continues to be called. Is my NSTimer TRON's answer to the Highlander, or is there something else going on?

Answer 1

NSTimer takes selector that should take one parameter as NSTimer * , here is the cite from Apple's documentation

The selector must correspond to a method that returns void and takes a single argument. The timer passes itself as the argument to this method.

Try to change the signature of your executeFastForward method like this:

-(void) executeFastForward:(NSTimer *)timer

than you can invalidate the timer passed as an argument, which will actually be the fired timer object

Answer 2

Well, after a LOT of experimentation (and being inspired by the if statement in this answer to an unrelated but similar question) I finally found a solution: don't check for the end of the gesture in the executeFastForward method, but rather the startFastForward method. Also, it turns out the startFastForward method was being called over and over, re-creating the timer, so the if statement also stops that by restricting the timer to UIGestureRecognizerStateBegan .

Here's the working code, for anyone who wants it:

- (IBAction)startFastForward:(UIGestureRecognizer *)gestureRecognizer {
    if(gestureRecognizer.state == UIGestureRecognizerStateBegan) {
        _timerFastForward = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(executeFastForward) userInfo:nil repeats:YES];
    } else if(gestureRecognizer.state == UIGestureRecognizerStateEnded) {
        [self endFastForward:self];
    }
}

- (void)executeFastForward {
    [_avPlayer seekToTime:CMTimeMake(CMTimeGetSeconds([_avPlayer currentTime]) + 10, 1)];
}

- (IBAction)endFastForward:(id)sender {
    [_timerFastForward invalidate];
    _timerFastForward = nil;
}