确定当前本地时间是否在两次之间（忽略日期部分）

Question

考虑到Cocoa-Touch（iPhone上的Objective-C）没有NSTime，并且NSStrings和NSZtring的时区分别是两次，你如何计算当前LOCAL时间是否在这两次之间。请记住，时间字符串中的日期并不重要，并且填充了虚拟日期。

例如：

 TimeZone: Pacific Time (US & Canada)
 Start Time: 2000-01-01T10:00:00Z
 End Time: 2000-01-01T17:00:00Z

 Local Time: now

如何确认当地时间是否在指定的时间范围之间（确保首先将开始/结束时间转换为正确的时区）？

Answer 1

这个问题的最大问题似乎来自于时间可能跨越两天（原来他们可能没有，但是当你进行时区转换时，他们可能会这样做）。因此，如果我们完全忽略给定的日期信息，则必须对如何处理这些日期跨度做出一些假设。你的问题并不完全是关于如何处理这个问题（即我不知道你想要实现的目标）所以这里只是一种方法，这可能不是你想要的，但是希望它能引导你朝着正确的方向前进：

• 将给定的字符串解析为NSDate个对象，忽略日期信息（结果：处理时间使得它们被假定为同一天）并执行时区转换
• 获取从早期NSDate到后期NSDate
的时间间隔
• 今天早些时候为“创建”NSDate对象和“昨天在给定时间”
• 比较从这两个NSDate到当前日期/时间的时间间隔到两个给定日期/时间之间的时间间隔

另请注意，"Pacific Time (US & Canada)"无法理解您提供的格式（NSTimeZone）的时区字符串，因此您需要在那里进行一些转换。

这是一个代码示例（我在OS X上写了这个，因为我没有iPhone SDK所以希望所有使用过的API也可以在iPhone上使用）：

- (BOOL)checkTimes
{
    // won't work:
    //NSString *tzs = @"Pacific Time (US & Canada)";
    // 
    // will work (need to translate given timezone information
    // to abbreviations accepted by NSTimeZone -- won't cover
    // that here):
    NSString *tzs = @"PST";

    NSString *ds1 = @"2000-01-01T10:00:00Z";
    NSString *ds2 = @"2000-01-01T17:00:00Z";

    // remove dates from given strings (requirement was to ignore
    // the dates completely)
    ds1 = [ds1 substringFromIndex:11];
    ds2 = [ds2 substringFromIndex:11];

    // remove the UTC time zone designator from the end (don't know
    // what it's doing there since the time zone is given as a
    // separate field but I'll assume for the sake of this example
    // that the time zone designator for the given dates will
    // always be 'Z' and we'll always ignore it)
    ds1 = [ds1 substringToIndex:8];
    ds2 = [ds2 substringToIndex:8];

    // parse given dates into NSDate objects
    NSDateFormatter *df = [[[NSDateFormatter alloc] init] autorelease];
    [df setDateFormat:@"HH:mm:ss"];
    [df setTimeZone:[NSTimeZone timeZoneWithAbbreviation:tzs]];
    NSDate *date1 = [df dateFromString:ds1];
    NSDate *date2 = [df dateFromString:ds2];

    // get time interval from earlier to later given date
    NSDate *earlierDate = date1;
    NSTimeInterval ti = [date2 timeIntervalSinceDate:date1];
    if (ti < 0)
    {
        earlierDate = date2;
        ti = [date1 timeIntervalSinceDate:date2];
    }

    // get current date/time
    NSDate *now = [NSDate date];

    // create an NSDate for today at the earlier given time
    NSDateComponents *todayDateComps = [[NSCalendar currentCalendar]
                                        components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit
                                        fromDate:now];
    NSDateComponents *earlierTimeComps = [[NSCalendar currentCalendar]
                                          components:NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit
                                          fromDate:earlierDate];
    NSDateComponents *todayEarlierTimeComps = [[[NSDateComponents alloc] init] autorelease];
    [todayEarlierTimeComps setYear:[todayDateComps year]];
    [todayEarlierTimeComps setMonth:[todayDateComps month]];
    [todayEarlierTimeComps setDay:[todayDateComps day]];
    [todayEarlierTimeComps setHour:[earlierTimeComps hour]];
    [todayEarlierTimeComps setMinute:[earlierTimeComps minute]];
    [todayEarlierTimeComps setSecond:[earlierTimeComps second]];
    NSDate *todayEarlierTime = [[NSCalendar currentCalendar]
                                dateFromComponents:todayEarlierTimeComps];

    // create an NSDate for yesterday at the earlier given time
    NSDateComponents *minusOneDayComps = [[[NSDateComponents alloc] init] autorelease];
    [minusOneDayComps setDay:-1];
    NSDate *yesterday = [[NSCalendar currentCalendar]
                         dateByAddingComponents:minusOneDayComps
                         toDate:now
                         options:0];
    NSDateComponents *yesterdayDateComps = [[NSCalendar currentCalendar]
                                            components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit
                                            fromDate:yesterday];
    NSDateComponents *yesterdayEarlierTimeComps = [[[NSDateComponents alloc] init] autorelease];
    [yesterdayEarlierTimeComps setYear:[yesterdayDateComps year]];
    [yesterdayEarlierTimeComps setMonth:[yesterdayDateComps month]];
    [yesterdayEarlierTimeComps setDay:[yesterdayDateComps day]];
    [yesterdayEarlierTimeComps setHour:[earlierTimeComps hour]];
    [yesterdayEarlierTimeComps setMinute:[earlierTimeComps minute]];
    [yesterdayEarlierTimeComps setSecond:[earlierTimeComps second]];
    NSDate *yesterdayEarlierTime = [[NSCalendar currentCalendar]
                                dateFromComponents:yesterdayEarlierTimeComps];

    // check time interval from [today at the earlier given time] to [now]
    NSTimeInterval ti_todayEarlierTimeTillNow = [now timeIntervalSinceDate:todayEarlierTime];
    if (0 <= ti_todayEarlierTimeTillNow && ti_todayEarlierTimeTillNow <= ti)
        return YES;

    // check time interval from [yesterday at the earlier given time] to [now]
    NSTimeInterval ti_yesterdayEarlierTimeTillNow = [now timeIntervalSinceDate:yesterdayEarlierTime];
    if (0 <= ti_yesterdayEarlierTimeTillNow && ti_yesterdayEarlierTimeTillNow <= ti)
        return YES;

    return NO;
}

Answer 2

您应该查看NSCalendar和NSDateComponents。我正在使用它们为iPhone应用程序做一些日期数学运算。我没有看到内置方法直接做你想要的东西，但是你可以把它分成我期望的碎片来解决它？

Answer 3

您应该能够使用NSDate和NSDateFormatter的组合来完成您想要做的事情。

NSDateFormatter有dateFromString:方法可让您将字符串转换为NSDate个对象，然后您可以使用compare: NSDate方法进行比较两个针对[NSDate date]的当前时间。

（NSDate包含日期和时间）