Objective c 如何从NSDateFormatter计算时间差

我使用以下代码将2个标签设置为当前时间：

NSDateFormatter *dateformatter = [[NSDateFormatter alloc] init];
        [dateformatter setDateFormat:@"hh:mma"];
        time2.text = [dateformatter stringFromDate:[NSDate date]];
        [dateformatter release];
        labelCount++;

---

单击按钮时，标签1将更改为当前时间，再次单击按钮时，标签2将更改为当前时间，但我希望能够更改第三个标签以显示这些时间之间的差异。任何帮助/指导都将不胜感激。

[date2 TimeIntervalsInceetDate:date1]将提供以秒为单位的时间间隔，但如果您希望将差值显示为小时：分钟，则此方法也适用

NSTimeInterval secondsBetween = [date2 timeIntervalSinceDate:date1];

- (IBAction)updateTime:(id)sender {
static NSUInteger labelCount = 0;

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"hh:mma"];
NSDate *date1 = nil;
NSDate *date2 = nil;
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *dateComponents;

switch (labelCount) {
    case 0:
        self.time1.text = [dateFormatter stringFromDate:[NSDate date]];
        labelCount++;
        break;
    case 1:
        self.time2.text = [dateFormatter stringFromDate:[NSDate date]];
        labelCount++;
        break;
    case 2:
        date1 = [dateFormatter dateFromString:self.time1.text];
        date2 = [dateFormatter dateFromString:self.time2.text];
        NSUInteger calendarUnits = NSHourCalendarUnit | NSMinuteCalendarUnit;
        dateComponents = [calendar components:calendarUnits fromDate:date1 toDate:date2 options:0];
        self.time3.text = [NSString stringWithFormat:@"%i:%i", [dateComponents hour], [dateComponents minute]];
        labelCount = 0;
        break;
    default:
        break;
}

}

注意：如果您没有使用arc，那么您需要将适当的版本添加到此代码中