当我尝试在我的应用程序中以模态方式显示视图控制器时，这是我得到的错误：
*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<KVPasscodeViewController 0x8b815a0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key instructionLabel.'
*** Call stack at first throw:
(
0 CoreFoundation 0x011185a9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x0126c313 objc_exception_throw + 44
2 CoreFoundation 0x011184e1 -[NSException raise] + 17
3 Foundation 0x00aea677 _NSSetUsingKeyValueSetter + 135
4 Foundation 0x00aea5e5 -[NSObject(NSKeyValueCoding) setValue:forKey:] + 285
5 UIKit 0x0056630c -[UIRuntimeOutletConnection connect] + 112
6 CoreFoundation 0x0108e8cf -[NSArray makeObjectsPerformSelector:] + 239
7 UIKit 0x00564d23 -[UINib instantiateWithOwner:options:] + 1041
8 UIKit 0x00566ab7 -[NSBundle(UINSBundleAdditions) loadNibNamed:owner:options:] + 168
9 UIKit 0x0041c628 -[UIViewController _loadViewFromNibNamed:bundle:] + 70
10 UIKit 0x0041a134 -[UIViewController loadView] + 120
11 UIKit 0x0041a00e -[UIViewController view] + 56
12 UIKit 0x00418482 -[UIViewController contentScrollView] + 42
13 UIKit 0x00428f25 -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] + 48
14 UIKit 0x00427555 -[UINavigationController _layoutViewController:] + 43
15 UIKit 0x00428870 -[UINavigationController _startTransition:fromViewController:toViewController:] + 524
16 UIKit 0x0042332a -[UINavigationController _startDeferredTransitionIfNeeded] + 266
17 UIKit 0x0053e2e9 -[UILayoutContainerView layoutSubviews] + 226
18 QuartzCore 0x002a6a5a -[CALayer layoutSublayers] + 181
19 QuartzCore 0x002a8ddc CALayerLayoutIfNeeded + 220
20 QuartzCore 0x002a8ed0 -[CALayer layoutIfNeeded] + 111
21 UIKit 0x0041b58a -[UIViewController window:willAnimateRotationToInterfaceOrientation:duration:] + 587
22 UIKit 0x0039255f -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:] + 4347
23 UIKit 0x00619619 -[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:] + 1381
24 UIKit 0x0041e65d -[UIViewController presentModalViewController:withTransition:] + 3478
25 DearMe 0x00011ca1 -[NotificationViewController addPasscode] + 273
26 UIKit 0x0036a4fd -[UIApplication sendAction:to:from:forEvent:] + 119
27 UIKit 0x003fa799 -[UIControl sendAction:to:forEvent:] + 67
28 UIKit 0x003fcc2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
29 UIKit 0x003fb7d8 -[UIControl touchesEnded:withEvent:] + 458
30 UIKit 0x0038eded -[UIWindow _sendTouchesForEvent:] + 567
31 UIKit 0x0036fc37 -[UIApplication sendEvent:] + 447
32 UIKit 0x00374f2e _UIApplicationHandleEvent + 7576
33 GraphicsServices 0x015f2992 PurpleEventCallback + 1550
34 CoreFoundation 0x010f9944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
35 CoreFoundation 0x01059cf7 __CFRunLoopDoSource1 + 215
36 CoreFoundation 0x01056f83 __CFRunLoopRun + 979
37 CoreFoundation 0x01056840 CFRunLoopRunSpecific + 208
38 CoreFoundation 0x01056761 CFRunLoopRunInMode + 97
39 GraphicsServices 0x015f11c4 GSEventRunModal + 217
40 GraphicsServices 0x015f1289 GSEventRun + 115
41 UIKit 0x00378c93 UIApplicationMain + 1160
42 DearMe 0x000029df main + 127
43 DearMe 0x00002955 start + 53
44 ??? 0x00000001 0x0 + 1
)
terminate called after throwing an instance of 'NSException'
有关为何可能造成这种情况的任何想法？
编辑：给出错误的代码：
KVPasscodeViewController *passcodeController = [[KVPasscodeViewController alloc] init];
passcodeController.delegate = self;
UINavigationController *passcodeNavigationController = [[UINavigationController alloc] initWithRootViewController:passcodeController];
[self.navigationController presentModalViewController:passcodeNavigationController animated:YES];
[passcodeNavigationController release];
[passcodeController release];
答案 0 :(得分：1)
这是因为你有一个插座指向该视图控制器的XIB中的'instructionLabel'。
答案 1 :(得分：1)
您的.xib文件最有可能指向不存在的标签。如果您在Interface Builder中添加UILabel，将其附加到存在instructionLabel的代码中，然后从代码中删除instructionLabel，则会发生这种情况，但忘记更新.xib }。