當項目中要用到倒計時的時候，直接把代碼拷過去

int secondsCountDown; //倒計時總時長  
NSTimer *countDownTimer;  
UILabel *labelText;

然后具體實現(xiàn)

//創(chuàng)建UILabel 添加到當前view  
labelText=[[UILabel alloc]initWithFrame:CGRectMake(10, 120, 120, 36)];  
[self.view addSubview:labelText];  

//設置倒計時總時長  
secondsCountDown = 60;//60秒倒計時  
//開始倒計時  
countDownTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timeFireMethod) userInfo:nil repeats:YES]; 

//啟動倒計時后會每秒鐘調用一次方法 timeFireMethod  

//設置倒計時顯示的時間  
labelText.text=[NSString stringWithFormat:@"%d",secondsCountDown]; 

實現(xiàn)每秒鐘執(zhí)行的方法

-(void)timeFireMethod{  
//倒計時-1  
secondsCountDown--;  
//修改倒計時標簽現(xiàn)實內容  
labelText.text=[NSString stringWithFormat:@"%d",secondsCountDown];  
//當?shù)褂嫊r到0時，做需要的操作，比如驗證碼過期不能提交  
if(secondsCountDown==0){  
    [countDownTimer invalidate];  
    [labelText removeFromSuperview];  
}  
}