iphone - 倒数计时器从 4 到 1 开始

Question

当我开始玩测验时，计时器开始倒计时“4…3…2…1…”。我想在测验的第一个问题中添加这个倒计时。倒计时后显示第一个问题。

任何人都可以帮助我吗

我正在尝试这样做，但我没有得到倒计时的格式。

NSTimer *timer_total = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0 target:self selector:@selector(updateTimer) userInfo:nil repeats:YES];

- (void)updateTimer
{
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate_total];
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    self.df_total = [[NSDateFormatter alloc] init];
    [self.df_total  setDateFormat:@"mm:ss"];
    [self.df_total setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString=[self.df_total stringFromDate:timerDate];
    self.lbl_total_Timer.text = timeString;
}

Answer 1

你可以这样做

int currentTime;
- (IBAction)start{

    currentTime = 5;
    lbl=[[UILabel alloc]init];
    //creates and fires timer every second
    myTimer = [[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(showTime) userInfo:nil repeats:YES]retain];
}

-(void)showTime{


    if(currentTime==0)
    {
        [myTimer invalidate];
        myTimer = nil;
    }
    else{


    currentTime--;
    lbl.text = [NSString stringWithFormat:@"%.2d", currentTime];
    }
    NSLog(@"my lable == %@",lbl.text);


}

- (void)viewWillAppear:(BOOL)animated 
{
    [self start];
    [super viewWillAppear:YES];

}