- (void)viewDidLoad{    [super viewDidLoad];    // Do any additional setup after loading the view.        //label    label=[[UILabel alloc]initWithFrame:CGRectMake(50, 100, 200, 200)];    label.backgroundColor=[UIColor redColor];    [self.view addSubview:label];        //定时器    [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateTime) userInfo:nil repeats:YES];        dateFormatter = [[NSDateFormatter alloc] init];    [dateFormatter setDateFormat:@"HH:mm:ss"];    }- (void)updateTime{    label.text = [dateFormatter stringFromDate:[NSDate date]];}