我有以下崩溃报告，无法导致崩溃。因为我在任何地方使用过长度字 你对这次事故的原因有任何了解吗？
Thread : Fatal Exception: NSInvalidArgumentException
0 CoreFoundation 0x0000000182b78f5c __exceptionPreprocess
1 libobjc.A.dylib 0x000000019776bf80 objc_exception_throw
2 CoreFoundation 0x0000000182b7fc6c __methodDescriptionForSelector
3 CoreFoundation 0x0000000182b7cc14 ___forwarding___
4 CoreFoundation 0x0000000182a80dcc _CF_forwarding_prep_0
5 UIKit 0x00000001880da13c -[UILabel _textRectForBounds:limitedToNumberOfLines:includingShadow:]
6 UIKit 0x00000001880da030 -[UILabel _intrinsicSizeWithinSize:]
7 UIKit 0x00000001881d5328 -[UILabel intrinsicContentSize]
8 UIKit 0x00000001881d5188 -[UIView(UIConstraintBasedLayout) _generateContentSizeConstraints]
9 UIKit 0x00000001881d4b9c -[UIView(UIConstraintBasedLayout) _updateContentSizeConstraints]
10 UIKit 0x00000001881d0c3c -[UIView(AdditionalLayoutSupport) updateConstraints]
11 UIKit 0x00000001881d4940 -[UILabel updateConstraints]
12 UIKit 0x00000001888f9e8c -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
13 UIKit 0x00000001888fa0f4 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
14 UIKit 0x00000001888f9dbc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
15 UIKit 0x00000001888fa0f4 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
16 UIKit 0x00000001888f9dbc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
17 UIKit 0x00000001888fa0f4 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
18 UIKit 0x00000001888f9dbc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
19 Foundation 0x0000000183a14aa0 -[NSISEngine withBehaviors:performModifications:]
20 UIKit 0x00000001881d3958 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:]
21 UIKit 0x00000001888fa0c8 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
22 UIKit 0x00000001888f9dbc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
23 UIKit 0x00000001888fa0f4 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
24 UIKit 0x00000001888f9dbc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
25 UIKit 0x00000001888fa0f4 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
26 UIKit 0x00000001888f9dbc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
27 UIKit 0x00000001888fa0f4 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:]
28 UIKit 0x00000001881d483c __60-[UIView(AdditionalLayoutSupport) updateConstraintsIfNeeded]_block_invoke
29 UIKit 0x00000001881d3968 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:]
30 UIKit 0x00000001881d4470 -[UIView(AdditionalLayoutSupport) updateConstraintsIfNeeded]
31 UIKit 0x00000001888fa798 -[UIView(AdditionalLayoutSupport) _updateConstraintsAtEngineLevelIfNeeded]
32 UIKit 0x00000001883d1fcc -[UIView(Hierarchy) _updateConstraintsAsNecessaryAndApplyLayoutFromEngine]
33 UIKit 0x00000001880cb038 -[UIView(CALayerDelegate) layoutSublayersOfLayer:]
34 QuartzCore 0x00000001878d1f14 -[CALayer layoutSublayers]
35 QuartzCore 0x00000001878ccb20 CA::Layer::layout_if_needed(CA::Transaction*)
36 QuartzCore 0x00000001878cc9e0 CA::Layer::layout_and_display_if_needed(CA::Transaction*)
37 QuartzCore 0x00000001878cc07c CA::Context::commit_transaction(CA::Transaction*)
38 QuartzCore 0x00000001878cbdd0 CA::Transaction::commit()
39 UIKit 0x00000001880ce0dc _UIApplicationHandleEventQueue
40 CoreFoundation 0x0000000182b305a4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
41 CoreFoundation 0x0000000182b30038 __CFRunLoopDoSources0
42 CoreFoundation 0x0000000182b2dd38 __CFRunLoopRun
43 CoreFoundation 0x0000000182a5cdc0 CFRunLoopRunSpecific
44 GraphicsServices 0x000000018dbb0088 GSEventRunModal
45 UIKit 0x0000000188136f60 UIApplicationMain
46 Olgera 0x000000010016c938 main (main.m:15)
47 libdyld.dylib 0x0000000197f968b8 start
另外我有疑问UILabel的长度属性是否导致这个或者NSNull对象是另一个类型的对象？
答案 0 :(得分：3)
[NSNull null]是一个特殊的单例值，用于表示不允许null的集合类型中的nil值，例如NSArray和NSDictionary 。
如果您知道来自服务器的特定值可以是null，那么在尝试将其视为其他值之前需要检查该值
NSDictionary *data = ...
NSString *name = [data objectForKey:@"name"];
// This will cause a crash if the value of the
// `name` key was `null` since objectForKey:
// will return [NSNull null]
if ([name length] > 0) {
// Do something
}
您要做的是在以任何方式使用之前检查该值是否为null
if (name != [NSNull null]) {
if ([name length] > 0) {
// Do something
}
}