我尝试在nil中添加NSDictionary日期时遇到了崩溃。
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:会返回nil并且崩溃。
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，我确信这种情况发生在10月18日的巴西，Daylight Saving Time occured。
答案 0 :(得分：1)
This answer和@DarkDust的comment指出了我正确的方向。
这确实是巴西午夜发生的夏令时问题。因此，10月17日至18日，没有午夜。因为我将日期格式设置为y-M-d，dateFromString:试图在当地午夜返回一个不存在的日期，因此返回nil。
重现的步骤：
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，它会为此时区返回2015-10-18 01:00:00之类的日期。