nstimeinterval
想在程序开始或者进入某个界面 ，到结束程序或退出某个界面，获取到这个持续时间. 获取到这个时间还需要转化一个取得时分秒.
-(NSString *)getCurrentTime
{
NSDateformatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSString *dateTime = [formatter stringFromDate:[NSDate date]];
self.startTime = dateTime;
return startTime;
}
date1代表开始时间，在开始计时的地方调用 [self getCurrentTime]; 在结束时的方法里写如下代码：NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *date1 = [formatter dateFromString:startTime];
NSDate *date2 = [NSDate date];
NSTimeInterval aTimer = [date2 timeIntervalSinceDate:date1];
int hour = (int)(aTimer/3600);
int minute = (int)(aTimer - hour*3600)/60;
int second = aTimer - hour*3600 - minute*60;
NSString *dural = [NSString stringWithFormat:@"%d时%d分%d秒", hour, minute,second];