NSDateFormatter 的 dateFromString 返回 null 与来自 stringFromDate 的日期 [重复]

Question

我在尝试在 NSDictionary 中添加 nil 日期时发生了崩溃。

我的代码如下所示：

625  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
626  NSCalendar *currentCalendar = [NSCalendar autoupdatingCurrentCalendar];
627  NSDate *todayDate = [NSDate date];
628
629  NSDateComponents *dateComponents = [currentCalendar components:NSUIntegerMax fromDate:todayDate];
630
631  NSMutableArray *lastDates = [[NSMutableArray alloc] init];
632
633  dateFormatter.dateFormat = @"y-M-d";
634
635  for (NSInteger i = 0; i < 7; i++) {
636      NSDate *date = [currentCalendar dateFromComponents:dateComponents];
637
638      dateComponents.day--;
639
640      [lastDates addObject:[dateFormatter stringFromDate:date]];
641  }
642
643  NSString *query = @"SELECT date FROM table";
644  NSArray *completedDates = [ZeeSQLiteHelper readQueryFromDB:query];
645
646  NSMutableDictionary *completedLessons = [[NSMutableDictionary alloc] init];
647
648  for (NSString *date in lastDates) {
649      BOOL completed;
650
651      if ([completedDates containsObject:@{ @"date" : date }]) {
652          completed = YES;
653   } else {
654       completed = NO;
655   }
656
657   completedLessons[[dateFormatter dateFromString:date]] = @(YES); // crash
658  }

出于某种原因，有时dateFromString: 返回nil 并崩溃。

崩溃报告：

0     CoreFoundation      0    x231d068b    __exceptionPreprocess + 124
1     libobjc.A.dylib     0    x3458ae17    objc_exception_throw + 36
2     CoreFoundation      0    x230ec8fb    -[__NSDictionaryM setObject:forKey:] + 840
3     MyApp               0    x00148df7    -[MyClass myMethod] (MyClass.m:657)
4     MyApp               0    x001406f3    -[MySecondViewController mySecondVCMethod] (MySecondViewController.m:250)
5     MyApp               0    x0013f8ed    -[MySecondViewController viewDidLoad] (MySecondViewController.m:92)
6     UIKit               0    x2729443d    -[UIViewController loadViewIfRequired] + 1106
7     UIKit               0    x27293fcd    -[UIViewController view] + 22
8     UIKit               0    x27abb559    -[_UIFullscreenPresentationController _setPresentedViewController:] + 70
9     UIKit               0    x275c9339    -[UIPresentationController initWithPresentedViewController:presentingViewController:] + 110
10    UIKit               0    x275ec473    -[UIViewController _presentViewController:withAnimationController:completion:] + 3536
11    UIKit               0    x275eeac5    __62-[UIViewController presentViewController:animated:completion:]_block_invoke + 334
12    UIKit               0    x275eed31    -[UIViewController _performCoordinatedPresentOrDismiss:animated:] + 414
13    UIKit               0    x27388701    -[UIViewController presentViewController:animated:completion:] + 142
14    MyApp               0    x00223429    -[MyFirstViewController myFirstVCSecondMethod] (MyFirstViewController.m:775)
15    MyApp               0    x00221edb    -[MyFirstViewController myFirstVCFirstMethod:] (MyFirstViewController.m:631)
16    UIKit               0    x272ca795    -[UIApplication sendAction:to:from:forEvent:] + 78
17    UIKit               0    x272ca725    -[UIControl sendAction:to:forEvent:] + 62
18    UIKit               0    x272b354b    -[UIControl _sendActionsForEvents:withEvent:] + 444
19    UIKit               0    x272ca085    -[UIControl touchesEnded:withEvent:] + 602
20    UIKit               0    x27286d33    _UIGestureRecognizerUpdate + 10768
21    UIKit               0    x272c36f9    -[UIWindow _sendGesturesForEvent:] + 902
22    UIKit               0    x272c2e43    -[UIWindow sendEvent:] + 620
23    UIKit               0    x272947e5    -[UIApplication sendEvent:] + 202
24    UIKit               0    x27292fdf    _UIApplicationHandleEventQueue + 4932
25    CoreFoundation      0    x23193c3f    __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 12
26    CoreFoundation      0    x2319382d    __CFRunLoopDoSources0 + 450
27    CoreFoundation      0    x23191b9b    __CFRunLoopRun + 792
28    CoreFoundation      0    x230e5249    CFRunLoopRunSpecific + 518
29    CoreFoundation      0    x230e5035    CFRunLoopRunInMode + 106
30    GraphicsServices    0    x2c1c8ad1    GSEventRunModal + 158
31    UIKit               0    x272fa899    UIApplicationMain + 142
32    MyApp               0    x00152f83    main (main.m:16)
33    libdyld.dylib       0    x34cd6873    start + 0

另外，我有 99% 的把握这发生在巴西，10 月 18 日，Daylight Saving Time occured。

Answer 1

This answer 和@DarkDust 的comment 为我指明了正确的方向。

巴西的夏令时确实是在午夜时分出现的问题。因此，在 10 月 17 日至 18 日期间，没有午夜。因此，因为我将日期格式设置为 y-M-d，dateFromString: 试图返回本地午夜的日期，但该日期不存在，因此它返回了 nil。

重现步骤：

dateFormatter.timeZone = [NSTimeZone timeZoneWithName:@"America/Sao_Paulo"];
NSLog([dateFormatter dateFromString:@"2015-10-18"]); // returns nil

我仍然需要找到一个解决方案，让我在这个时区返回像 2015-10-18 01:00:00 这样的日期。