TL&DR;
使用 UIAppearance 代理设置 UIBarButtonItem 子类的自定义属性会导致“无法识别的选择器”异常，因为 setter 可能由 UIAppearance 转发到 UINavigationButton，而不是栏按钮本身。
SDK 概述
我正在使用带有 Xcode 5 DP5 的 iOS 7 Beta 5 SDK。但是请不要告诉我它在 NDA 下，因为我不会在这个问题中讨论任何新特性或新类。我通知你我的SDK，因为可以发现它只是beta软件中的一个错误。
我做了什么
我将 a 子类UIBarButtonItem化并在头文件中创建了一个自定义属性：
@property (nonatomic, strong) NSString *mySubclassedProperty UI_APPEARANCE_SELECTOR;
我的 setter 和 getter 如下所示：
- (void)setMySubclassedProperty:(NSString *)mySubclassedProperty {
_mySubclassedProperty = mySubclassedProperty;
NSLog(@"%p %s %@", self, __PRETTY_FUNCTION__, mySubclassedProperty);
}
没什么特别的吧？但它根本不起作用UIAppearance。当我尝试在我的应用程序的委托中设置默认外观时，它不会给我任何错误，也不会发出警告。
[[AKBarButtonItem appearance] setMySubclassedProperty:@"GLOBALLY ASSIGNED"];
迷恋;撞车;崩溃
它似乎像一个魅力，除了当我尝试设置一个实例时它崩溃的AKBarButtonItem事实self.navigationItem.rightBarButtonItem：
self.navigationItem.rightBarButtonItem = [[AKBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAction target:nil action:nil];
回溯看起来像这样：
2013-08-13 14:30:08.551 UIBarButtonItem Subclass Demo[1512:a0b] -[UINavigationButton setMySubclassedProperty:]: unrecognized selector sent to instance 0x8c42710
2013-08-13 14:30:08.556 UIBarButtonItem Subclass Demo[1512:a0b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UINavigationButton setMySubclassedProperty:]: unrecognized selector sent to instance 0x8c42710'
*** First throw call stack:
(
0 CoreFoundation 0x0173b6f4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x014bb8b6 objc_exception_throw + 44
2 CoreFoundation 0x017d8983 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
3 CoreFoundation 0x0172ba1b ___forwarding___ + 1019
4 CoreFoundation 0x0172b5fe _CF_forwarding_prep_0 + 14
5 CoreFoundation 0x0172fe2d __invoking___ + 29
6 CoreFoundation 0x0172fd3a -[NSInvocation invoke] + 362
7 CoreFoundation 0x0172feba -[NSInvocation invokeWithTarget:] + 74
8 UIKit 0x00763255 workaround10030904InvokeWithTarget + 824
9 UIKit 0x0075dea8 +[_UIAppearance _applyInvocationsTo:window:matchingSelector:] + 4497
10 UIKit 0x0075e299 +[_UIAppearance _applyInvocationsTo:window:] + 55
11 UIKit 0x0029ddcb -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 183
12 libobjc.A.dylib 0x014cd81f -[NSObject performSelector:withObject:] + 70
13 QuartzCore 0x03ac172a -[CALayer layoutSublayers] + 148
14 QuartzCore 0x03ab5514 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
15 QuartzCore 0x03ac3b55 -[CALayer(CALayerPrivate) layoutBelowIfNeeded] + 43
16 UIKit 0x00290886 -[UIView(Hierarchy) layoutBelowIfNeeded] + 595
17 UIKit 0x0029062d -[UIView(Hierarchy) layoutIfNeeded] + 74
18 UIKit 0x0050841e -[UIBarButtonItem(UIStatic) _leftRightImagePaddingForEdgeMarginInNavBarIsMini:] + 574
19 UIKit 0x002ea325 -[UINavigationBar _getTitleViewFrame:leftViewFrames:rightViewFrames:forItemAtIndex:returnedIdealWidthOfTextContent:availableLayoutWidthForTextContent:idealBackButtonWidth:] + 3522
20 UIKit 0x002ef2da -[UINavigationBar _getTitleViewFrame:leftViewFrames:rightViewFrames:forItemAtIndex:] + 591
21 UIKit 0x002ef59a -[UINavigationBar _getTitleViewFrame:leftViewFrames:rightViewFrames:] + 151
22 UIKit 0x002dc515 -[UINavigationBar _setLeftViews:rightViews:] + 1894
23 UIKit 0x002ca6c5 -[UINavigationItem updateNavigationBarButtonsAnimated:] + 188
24 UIKit 0x002cab63 -[UINavigationItem setObject:forLeftRightKeyPath:animated:] + 547
25 UIKit 0x002cb1ae -[UINavigationItem setRightBarButtonItem:animated:] + 171
26 UIKit 0x002cb0fe -[UINavigationItem setRightBarButtonItem:] + 48
27 UIBarButtonItem Subclass Demo 0x0000665e -[AKViewController viewDidLoad] + 222
28 UIKit 0x00345c18 -[UIViewController loadViewIfRequired] + 696
29 UIKit 0x00345eb4 -[UIViewController view] + 35
30 UIKit 0x00370369 -[UINavigationController rotatingSnapshotViewForWindow:] + 52
31 UIKit 0x00698e10 -[UIClientRotationContext initWithClient:toOrientation:duration:andWindow:] + 420
32 UIKit 0x00276ff2 -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:isRotating:] + 1495
33 UIKit 0x00276a16 -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:] + 82
34 UIKit 0x002768e8 -[UIWindow _setRotatableViewOrientation:updateStatusBar:duration:force:] + 117
35 UIKit 0x00276970 -[UIWindow _setRotatableViewOrientation:duration:force:] + 67
36 UIKit 0x00275a0a __57-[UIWindow _updateToInterfaceOrientation:duration:force:]_block_invoke + 120
37 UIKit 0x0027596c -[UIWindow _updateToInterfaceOrientation:duration:force:] + 400
38 UIKit 0x002766c3 -[UIWindow setAutorotates:forceUpdateInterfaceOrientation:] + 870
39 UIKit 0x00279c7e -[UIWindow setDelegate:] + 449
40 UIKit 0x0034a037 -[UIViewController _tryBecomeRootViewControllerInWindow:] + 180
41 UIKit 0x0026f91c -[UIWindow addRootViewControllerViewIfPossible] + 609
42 UIKit 0x00270146 -[UIWindow setRootViewController:] + 960
43 UIBarButtonItem Subclass Demo 0x00006a07 -[AKAppDelegate application:didFinishLaunchingWithOptions:] + 823
44 UIKit 0x0022d525 -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 309
45 UIKit 0x0022dd65 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1536
46 UIKit 0x00232578 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
47 UIKit 0x0024657c -[UIApplication handleEvent:withNewEvent:] + 3447
48 UIKit 0x00246ae9 -[UIApplication sendEvent:] + 85
49 UIKit 0x002341f5 _UIApplicationHandleEvent + 736
50 GraphicsServices 0x0365a33b _PurpleEventCallback + 776
51 GraphicsServices 0x03659e46 PurpleEventCallback + 46
52 CoreFoundation 0x016b6e95 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
53 CoreFoundation 0x016b6bcb __CFRunLoopDoSource1 + 523
54 CoreFoundation 0x016e18ac __CFRunLoopRun + 2156
55 CoreFoundation 0x016e0bf3 CFRunLoopRunSpecific + 467
56 CoreFoundation 0x016e0a0b CFRunLoopRunInMode + 123
57 UIKit 0x00231cad -[UIApplication _run] + 840
58 UIKit 0x00233f0b UIApplicationMain + 1225
59 UIBarButtonItem Subclass Demo 0x00006e9d main + 141
60 libdyld.dylib 0x01d77725 start + 0
)
libc++abi.dylib: terminating with uncaught exception of type NSException
经过一番检查，我奇怪地意识到setMySubclassedProperty:消息是发送到的UINavigationButton（这是UIButton用于导航栏、工具栏和搜索栏的私有子类）。我在 frame 中设置了按钮，26魔术UIAppearance在 frame 中执行10。
在 iOS 6 中，问题存在，但不同的消息被发送到UINavigationButton：
2013-08-13 14:35:58.316 UIBarButtonItem Subclass Demo[1591:c07] -[UINavigationButton _UIAppearance_setMySubclassedProperty:]: unrecognized selector sent to instance 0x810d600
2013-08-13 14:35:58.359 UIBarButtonItem Subclass Demo[1591:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UINavigationButton _UIAppearance_setMySubclassedProperty:]: unrecognized selector sent to instance 0x810d600'
*** First throw call stack:
(0x12b2012 0x10d7e7e 0x133d4bd 0x12a1bbc 0x12a194e 0x12a61bd 0x12a60d6 0x12a624a 0x68b9e8 0x68769c 0x687a95 0x291884 0x3088ca 0x28cf96 0x2934a4 0x28b89d 0x2cc646 0x2bc076 0x2bc517 0x2bcb66 0x2bcab6 0x665e 0x3261c7 0x326232 0x3264da 0x33d8e5 0x33d9cb 0x33dc76 0x33dd71 0x33e89b 0x33e9b9 0x33ea45 0x44420b 0x2952dd 0x10eb6b0 0x289dfc0 0x289233c 0x289deaf 0x3342bd 0x27cb56 0x27b66f 0x27b589 0x27a7e4 0x27a61e 0x27b3d9 0x27e2d2 0x32899c 0x275574 0x275cc1 0x6a07 0x242157 0x242747 0x24394b 0x254cb5 0x255beb 0x247698 0x24b8df9 0x24b8ad0 0x1227bf5 0x1227962 0x1258bb6 0x1257f44 0x1257e1b 0x24317a 0x244ffc 0x6e9d 0x1ab0725)
libc++abi.dylib: terminate called throwing an exception
扣除
我的第一个想法是：“UIAppearance 将设置器转发给 AKBarButtonItem，然后它就崩溃了”。但真的吗？在Peter Steinberger 的一篇文章中，我发现 Apple 正在使用一个特殊的_UIAppearance用于 bar items 的子类，称为_UIBarItemAppearance. 我想确认并设置一个符号断点，-[_UIBarItemAppearance forwardInvocation:]并且 lldb 在异常发生之前成功停止。
现在在我看来，Apple 正在做一些肮脏的逻辑-[_UIBarItemAppearance forwardInvocation:]来实现应该将哪个选择器发送到哪个实例，例如：
setBackgroundImage:forState:应该发送到UINavigationButtonsetBackButtonBackgroundImage:forState:barMetrics:至UIBarButtonItem- ...
他们的代码如下所示：
if (selector == @selector(setBackButtonBackgroundImage:forState:barMetrics:)) {
// forward to UIBarButtonItem
} else if (selector == @selector(setBackButtonBackgroundVerticalPositionAdjustment:forBarMetrics:)) {
// forward to UIBarButtonItem
} else if (...) {
// more forwarding to UIBarButtonItem
} else {
// forward to UINavigationButton
}
然后，根据我的推论，最后一条else语句导致setNiceBarButtonItemAttributes:选择器被发送到UINavigationButton，而不是UIBarButtonItem。如果是真的，我们就完蛋了。
示例代码
您可以在此处下载示例项目：http: //cl.ly/241I2A3U0a0y。
帮助
我只是做错了什么，还是一个错误？或者，苹果可能是故意的？任何帮助，将不胜感激。