的NSDate倒计时与NSInterval

Question

这里是我的代码：

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]) { 

} 

问题是， '如果（[currentTime的isEqualToString：nextTrigger]）' 从来都不是平等的。因为nextTrigger在它们相等之前更改为下一个时间段。这里是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 

我的代码的nextTrigger基本上是当前时间的最近一个分钟的四舍五入。此外，整个代码段每隔1秒钟处于一个重复的NSTimer中。

我该如何解决这个问题？

Answer 1

我有一个类似的问题。我所做的就是创建一个副本，并通过检查。（有一件事是同时拥有oldTrigger和newTrigger已申报）检查这个代码

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

如果你有代码想在下一整分钟过后触发，那么重复检查以确定是否已经过去了，效率很低。将该代码放在自己的方法中，并创建一个NSTimer以在适当的时候触发它。

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 ] ;