objective-c - 由于时区，NSDate 转换混乱

Question

我正在尝试在时间选择器上设置时间值，问题是由于时区问题导致时间混乱。这是我使用的代码片段：

 int targetmillisondsFromMidnight = [self.schedule.targetHour intValue]; // 59580000
    NSDate* todayMidnight = [NSCalendar.currentCalendar startOfDayForDate:[NSDate new]]; //2019-12-23 00:00:00 UTC
    NSTimeZone* timezone = [NSTimeZone defaultTimeZone];
    NSInteger seconds = [timezone secondsFromGMT];
    todayMidnight = [todayMidnight dateByAddingTimeInterval:seconds];
    NSDate* scheduleDate = [NSDate dateWithTimeInterval:targetmillisondsFromMidnight/1000 sinceDate:todayMidnight]; //2019-12-23 16:33:00 UTC

    NSCalendar *calendar = [NSCalendar currentCalendar];
    [calendar setTimeZone:[NSTimeZone defaultTimeZone]];
    NSDateComponents *components = [calendar components:(NSCalendarUnitHour | NSCalendarUnitMinute) fromDate:scheduleDate];

    [self.datePicker setTimeZone:[NSTimeZone defaultTimeZone]];
    [self.datePicker setDate:[calendar dateFromComponents:components] animated:YES];

当我这样做po [components hour]而不是得到 16 时，scheduleDate我得到 18。我该如何解决这个问题？我试图将时区更改为localTimeZone，timeZoneWithAbbreviation:@"GMT"但似乎没有任何效果。

Answer 1

It looks like you do superfluous conversion

Let's consider the following code

NSDate *date = [NSDate new]; // << in UTC always

NSCalendar *calendar = [NSCalendar currentCalendar];
[calendar setTimeZone:[NSTimeZone defaultTimeZone]]; // << in local 

NSDateComponents *components = [calendar components:
   (NSCalendarUnitHour | NSCalendarUnitMinute) fromDate:date]; // << converted to local

debug output:

  (lldb) po date
  2019-12-24 09:53:12 +0000

  (lldb) po components
  <NSDateComponents: 0x600003c78710> {
    Hour: 10
    Minute: 53