的NSDate倒計時與NSInterval

Question

這裏是我的代碼：

NSDate *currDate = [NSDate date]; 
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init]; 
[dateFormatter setDateFormat:@"HH:mm:ss"]; 
NSString *currentTime = [dateFormatter stringFromDate:currDate]; 

NSDate *now = [NSDate date]; 
int interval = 1*60; // one minute (minutes*60) 
long int nowSeconds = (long int) [now timeIntervalSince1970]; 
int secondsLeft = interval - (nowSeconds % interval); 

NSDate *nextIntervalDate = [NSDate dateWithTimeIntervalSince1970:nowSeconds+secondsLeft]; 

NSString *nextTrigger = [dateFormatter stringFromDate:nextIntervalDate]; 

timeRemaining.text = [NSString stringWithFormat:@"%02d:%02d", secondsLeft/60, secondsLeft%60]; 

NSLog([NSString stringWithFormat:@"%@:%@", currentTime, nextTrigger]); 

if ([currentTime isEqualToString:nextTrigger]) { 

} 

問題是， '如果（[currentTime的isEqualToString：nextTrigger]）' 從來都不是平等的。因爲nextTrigger在它們相等之前更改爲下一個時間段。這裏是NSLog：

2013-01-17 15:54:59.987 app[35987:c07] 15:54:59:15:55:00 
2013-01-17 15:54:59.997 app[35987:c07] 15:54:59:15:55:00  
2013-01-17 15:55:00.007 app[35987:c07] 15:55:00:15:56:00 <----RIGHT HERE 
2013-01-17 15:55:00.016 app[35987:c07] 15:55:00:15:56:00 

我的代碼的nextTrigger基本上是當前時間的最近一個分鐘的四捨五入。此外，整個代碼段每隔1秒鐘處於一個重複的NSTimer中。

我該如何解決這個問題？

Answer 1

我有一個類似的問題。我所做的就是創建一個副本，並通過檢查。（有一件事是同時擁有oldTrigger和newTrigger已申報）檢查這個代碼

NSDate *currDate = [NSDate date]; 
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init]; 
[dateFormatter setDateFormat:@"HH:mm:ss"]; 
NSString *currentTime = [dateFormatter stringFromDate:currDate]; 

NSDate *now = [NSDate date]; 
int interval = 1*60; // one minute (minutes*60) 
long int nowSeconds = (long int) [now timeIntervalSince1970]; 
int secondsLeft = interval - (nowSeconds % interval); 

NSDate *nextIntervalDate = [NSDate dateWithTimeIntervalSince1970:nowSeconds+secondsLeft]; 
oldTrigger = nextTrigger; 
nextTrigger = [dateFormatter stringFromDate:nextIntervalDate]; 

timeRemaining.text = [NSString stringWithFormat:@"%02d:%02d", secondsLeft/60, secondsLeft%60]; 

NSLog([NSString stringWithFormat:@"%@:%@", currentTime, nextTrigger]); 

if ([currentTime isEqualToString:oldTrigger]) { 

} 

Answer 2

如果你有代碼想在下一整分鐘過後觸發，那麼重複檢查以確定是否已經過去了，效率很低。將該代碼放在自己的方法中，並創建一個NSTimer以在適當的時候觸發它。

NSDate* date = [NSDate date] ; 
NSCalendar* calendar = [NSCalendar currentCalendar] ; 

NSDateComponents* secondsComponents = [calendar components:NSSecondCalendarUnit fromDate:date] ; 
NSTimeInterval secondsUntilNextWholeMinute = 60 - secondsComponents.second ; 
[NSTimer scheduledTimerWithTimeInterval:secondsUntilNextWholeMinute target:self selector:@selector(yourMethod) userInfo:nil repeats:NO ] ;