Change NSTimer interval after a certain number of fires

Question

In the following code, the NSTimer interval is set at 1 second between each picture. My goal is to change the interval after the first two pictures, hello.png and b

Answer 1

Make the timer object a member variable. Initially set animation time as 1 second. In the callback invalidate the timer and create a new one with 1 or 4 seconds depending on the counter.

@interface ViewController ()
@property (strong,nonatomic) NSMutableArray *images;
@property (strong,nonatomic) UIImageView *animationImageView;
{
    NSTimer *_timer;
}
@end

@implementation ViewController {
    NSInteger counter;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    NSArray *imageNames = @[@"hello.png",@"bye.png",@"helloagain.png",@"bye again"];

    self.images = [[NSMutableArray alloc] init];
    for (int i = 0; i < imageNames.count; i++) {
        [self.images addObject:[UIImage imageNamed:[imageNames objectAtIndex:i]]];
    }

    self.animationImageView = [[UIImageView alloc] initWithFrame:CGRectMake(60, 95, 86, 90)];
    self.animationImageView.image = self.images[0];
    [self.view addSubview:self.animationImageView];
    self.animationImageView.userInteractionEnabled = TRUE;

    UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(bannerTapped:)];
    singleTap.numberOfTapsRequired = 1;
    singleTap.numberOfTouchesRequired = 1;
    [self.animationImageView addGestureRecognizer:singleTap];
    _timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(changeImage:) userInfo:nil repeats:YES];
}


-(void)changeImage:(NSTimer *) timer {
     [_timer invalidate];
    if (counter == self.images.count - 1 ) {
        counter = 0;
    }else {
        counter ++;
    }
    if(counter == 0 || counter == 1)
    {
        _timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(changeImage:) userInfo:nil repeats:YES];
    }
    else if(counter == 2 || counter == 3)
    {
        _timer = [NSTimer scheduledTimerWithTimeInterval:4 target:self selector:@selector(changeImage:) userInfo:nil repeats:YES];
    }
    self.animationImageView.image = self.images[counter];
}