倒计时

首先在AppDelegate.h里定义几个属性

//时间

@property (assign,nonatomic) NSInteger time;

//显示时间变化的label

@property (strong,nonatomic) UILabel *label;

@property (retain,nonatomic)NSDate *backDate;

然后在AppDelegate.m中

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    

    self.window = [[UIWindowalloc] initWithFrame:[UIScreenmainScreen].bounds];

    self.window.backgroundColor = [UIColorwhiteColor];

    [self.windowmakeKeyAndVisible];

    

    //创建一个label用来显示倒计时开始

    _label = [[UILabelalloc] initWithFrame:CGRectMake(50,50, 200, 200)];

    _label.backgroundColor = [UIColororangeColor];

    _label.textAlignment =NSTextAlignmentCenter;

    _label.text =@"倒计时开始";

    [self.windowaddSubview:_label];

    

    //从100慢慢减少

    _time = 100;

    //开启定时器

    [NSTimerscheduledTimerWithTimeInterval:1target:selfselector:@selector(timerAction:)userInfo:nilrepeats:YES];

    

    return YES;

}

//定时器调用的方法

- (void)timerAction:(NSTimer *)timer{

    

    _label.text = [NSStringstringWithFormat:@"%ld",_time];

    if (_time ==0) {

        [timer invalidate];

    }

    _time--;

}

- (void)applicationWillResignActive:(UIApplication *)application {

   

    //取得当前的时间点

    _backDate = [[NSDatedate] retain];

    

}

就可以实现一个倒计时的小功能了！