IOS根据date计算时间差

IOS根据date计算时间差

NSDate *oldDate = [NSDate date];
NSDate *currentDate = [NSDate date];
NSLog(@"lastDate == %@",currentDate);

NSCalendar *cal = [NSCalendar currentCalendar];
unsigned int unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *dateComponents = [cal components:unitFlags fromDate:oldDate toDate:currentDate options:0];

float sec = [dateComponents hour]*3600 + [dateComponents minute]*60  + [dateComponents second];
NSLog(@"sec ==== %f",sec);