#import "MyViewController.h"

@interface MyViewController ()
{
    NSTimer *_timer;
}
@end

@implementation MyViewController

- (void)dealloc
{
    [_timer invalidate];
}


- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    _timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(changeCountdownTime) userInfo:nil repeats:YES];
    [[NSRunLoop currentRunLoop] addTimer:_timer forMode:NSRunLoopCommonModes];
}

- (void)changeCountdownTime
{
    // do something
}

- (void)back
{
    [self.navigationController popViewControllerAnimated:YES];
}