ios - Countdown and dismiss modal view -

i have modal view in countdown starts when user had performed action. @ end of countdown, modal view close. following procedure have written towards goal unfortunately, causing thread problems. there way rewrite in way not have potential thread issues?

- (void)countdown {     static int = 3;     if (i == 3) {         i--;         uiimage *three = [uiimage imagenamed:@"three"];         countdownflag = [[uiimageview alloc] initwithimage:three];         countdownflag.frame = cgrectmake(0, 370, countdownflag.frame.size.width, countdownflag.frame.size.height);         countdownflag.center = cgpointmake(width / 2, countdownflag.center.y);         [self.view addsubview:countdownflag];         [self performselector:@selector(countdown) withobject:nil afterdelay:0.5];     } else if (i == 2) {         i--;         uiimage *two = [uiimage imagenamed:@"two"];         [countdownflag setimage:two];         [self performselector:@selector(countdown) withobject:nil afterdelay:0.5];     } else if (i == 1) {         i--;         uiimage *one = [uiimage imagenamed:@"one"];         [countdownflag setimage:one];         [self performselector:@selector(countdown) withobject:nil afterdelay:0.5];     } else {         [self dismissviewcontrolleranimated:yes completion:nil];     } } 

edit: picture shows xcode tells me problem

more edit:

my code has changed reflect vadian's answer. here update

- (void)startcountdown {     nslog(@"starting count down");     counter = 3;     [nstimer scheduledtimerwithtimeinterval:0.5 target:self selector:@selector(countdown:) userinfo:nil repeats:yes]; }  - (void)countdown:(nstimer *)timer {      if (counter == 3) {         countdownflag = [[uiimageview alloc] init];         countdownflag.frame = cgrectmake(0, 370, countdownflag.frame.size.width, countdownflag.frame.size.height);         countdownflag.center = cgpointmake(width / 2, countdownflag.center.y);         dispatch_async(dispatch_get_main_queue(), ^{             [self.view addsubview:countdownflag];         });     } else if (counter == 0) {         [timer invalidate];         [self dismissviewcontrolleranimated:yes completion:nil];         return;     }     nsarray *imagenamearray = @[@"", @"one", @"two", @"three"];     uiimage *image = [uiimage imagenamed:imagenamearray[counter]];     dispatch_async(dispatch_get_main_queue(), ^{         [self.countdownflag setimage:image];     });     counter--; } 

i new guess problem lies in code calls countdown. here code this.

- (void)changelanguage:(bool) ismyanmar {     if (hasrun == yes) {         return;     }     hasrun = yes;      nsuserdefaults * userdefaults = [nsuserdefaults standarduserdefaults];     [userdefaults setbool:ismyanmar forkey:@"myanmar"];     [userdefaults synchronize];      [self updatecurrentlanguagetext];     if ([self ismyanmar]) {         [self changelanguageflag:@"myanmarflagbig"];     } else {         [self changelanguageflag:@"unitedkingdomflagbig"];     }      //>>>>>>>>>>>>>>>>>>>> problem here      [self startcountdown]; } 

any code runs after changing language code fails. problem there.

edit: the thread problem gone countdown isn't happening anymore.

after have moved code in changelanguage methods call it, problem mysteriously gone. (repetitive works.)

- (void)changelanguagetoenglish {     [thelock lock];     if (hasrun == yes) {         [thelock unlock];         return;     }     hasrun = yes;      [userdefaults setbool:false forkey:@"myanmar"];     [userdefaults synchronize];      [self updatecurrentlanguagetext];     if ([self ismyanmar]) {         [self changelanguageflag:@"myanmarflagbig"];     } else {         [self changelanguageflag:@"unitedkingdomflagbig"];     }      [self startcountdown];      [thelock unlock];  }  - (void)changelanguagetomyanmar {     [thelock lock];     if (hasrun == yes) {         [thelock unlock];         return;     }     hasrun = yes;      [userdefaults setbool:true forkey:@"myanmar"];     [userdefaults synchronize];      [self updatecurrentlanguagetext];     if ([self ismyanmar]) {         [self changelanguageflag:@"myanmarflagbig"];     } else {         [self changelanguageflag:@"unitedkingdomflagbig"];     }      [self startcountdown];      [thelock unlock];  } 

but problem countdown isn't happening anymore.

you use nstimer perform countdown , static variable counter.

the method startcountdown starts timer.

the method countdown:(nstimer *)timer called every 0.5 seconds. passed nstimer argument timer has been started. performs action according value , decrements counter. if counter 0, timer invalidated , controller dismissed.

static uint8 counter = 0;  - (void)startcountdown {   countdownflag = [[uiimageview alloc] init];   countdownflag.frame = cgrectmake(0, 370, countdownflag.frame.size.width, countdownflag.frame.size.height);   countdownflag.center = cgpointmake(width / 2, countdownflag.center.y);   [self.view addsubview:countdownflag];   counter = 3;   [nstimer scheduledtimerwithtimeinterval:0.5 target:self selector:@selector(countdown:) userinfo:nil repeats:yes]; }  - (void)countdown:(nstimer *)timer {   if (counter == 0) {     [timer invalidate];     [self dismissviewcontrolleranimated:yes completion:nil];     return;   }   nsarray *imagenamearray = @[@"", @"one", @"two", @"three"];   uiimage *image = [uiimage imagenamed:imagenamearray[counter]];   dispatch_async(dispatch_get_main_queue(), ^{     [self.countdownflag setimage:image];   });   counter--; 

}