objective c - Change NSTimer interval after a certain number of fires -

in following code, nstimer interval set @ 1 second between each picture. goal change interval after first 2 pictures, hello.png , bye.png, 4 seconds.

- (void)viewdidload {     [super viewdidload];      nsarray *imagenames = @[@"hello.png",@"bye.png",@"helloagain.png",@"bye again"];      self.images = [[nsmutablearray alloc] init];     (int = 0; < 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;        [nstimer scheduledtimerwithtimeinterval:1 target:self selector:@selector(changeimage:) userinfo:nil repeats:yes]; }   -(void)changeimage:(nstimer *) timer {     if (counter == self.images.count - 1 ) {         counter = 0;     }else {         counter ++;     }     self.animationimageview.image = self.images[counter]; } 

make timer object member variable. set animation time 1 second. in callback invalidate timer , create new 1 one or 4 seconds depending on 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];     (int = 0; < 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]; }