NSDateFormatter的dateFromString從stringFromDate返回null和日期

Question

我試圖在NSDictionary中添加一個nil日期的崩潰。

我的代碼如下所示：

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 } 

出於某種原因，有時，dateFromString:回報nil和崩潰。

崩潰報告：

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99％肯定這發生在巴西，在哪裏Daylight Saving Time occured 10月18日。

Answer 1

This answer和@ DarkDust的comment指出我正確的方向。

這確實是巴西午夜時分發生的夏令時問題。因此，10月17日至18日，沒有午夜。因爲我的日期格式設置爲y-M-d，所以dateFromString:正試圖在當地午夜返回一個不存在的日期，因此它返回nil。

重現步驟：

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

我還是要找出將返回我喜歡2015-10-18 01:00:00日期爲這個時區的解決方案。