ios - 神秘的 UIButton 崩溃

Question

我有一个 UITableViewCell，它有 2 个 UIButton 实例。两个按钮都有一个默认图像。只有“坏”按钮具有禁用状态的图像。仅此而已。

在单元类中，这两个按钮使用 IBOutlet 关键字声明为属性:

@property (nonatomic, readonly) IBOutlet UIButton* buttonCall;
@property (nonatomic, readonly) IBOutlet UIButton* buttonGPS;

.xib 中的 2 个按钮与类中的属性之间已建立连接。

因此，当加载 .xib 时，将完成以下操作:

MyCell* cell = (MyCell*)[tableView dequeueReusableCellWithIdentifier:cellID];
if (nil == cell)
{
    NSArray* nibContents = [[NSBundle mainBundle] loadNibNamed:@"MyCell" owner:nil options:nil];
    cell = [nibContents objectAtIndex:0];
    cell.selectionStyle = UITableViewCellSelectionStyleNone;
}

// gps button
[cell.buttonGPS setTitle:[NSString stringWithFormat:@"%d", indexPath.row] forState:UIControlStateNormal];
[cell.buttonGPS addTarget:self action:@selector(actionGPS:) forControlEvents:UIControlEventTouchUpInside];

if (...condition...)
{
    cell.buttonCall.enabled = NO;
    [cell.buttonCall removeTarget:self action:@selector(actionCall:) forControlEvents:UIControlEventTouchUpInside];
}
else
{
    cell.buttonCall.enabled = YES;
    [cell.buttonCall setTitle:[...TheTitleString...] forState:UIControlStateNormal];
    [cell.buttonCall addTarget:self action:@selector(actionCall:) forControlEvents:UIControlEventTouchUpInside];
}

当 View Controller 出现时，它会成功地通过 (UITableViewCell*)tableView:cellForRowAtIndexPath: 必要的次数。然后应用程序崩溃并显示以下堆栈:

0 kill
...
[UIButton imageRectForContentRect:]
[UIButton(UIButtonInternal) _setupImageView]
[UIButton layoutSubviews]
...
start

我删除了按钮的图像并开始与堆栈崩溃:

0 kill
...
[UIButton layoutSubviews]
...
start

我为按钮添加了一些标识符标签 - 仍然崩溃。

删除了“坏”按钮的 XCode-InterfaceBuilder 连接，崩溃停止了。但该按钮不起作用。

知道导致崩溃的原因吗？

调用堆栈是:

0   CoreFoundation                      0x013d406e __exceptionPreprocess + 206
1   libobjc.A.dylib                     0x019f0d0a objc_exception_throw + 44
2   CoreFoundation                      0x013d5ced -[NSObject doesNotRecognizeSelector:] + 253
3   CoreFoundation                      0x0133af00 ___forwarding___ + 432
4   CoreFoundation                      0x0133ace2 _CF_forwarding_prep_0 + 50
5   UIKit                               0x0086de3a -[UIButton imageRectForContentRect:] + 350
6   UIKit                               0x0086ed5b -[UIButton(UIButtonInternal) _setupImageView] + 158
7   UIKit                               0x0086e5f8 -[UIButton layoutSubviews] + 693
8   UIKit                               0x0069f322 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 178
9   CoreFoundation                      0x013d5e72 -[NSObject performSelector:withObject:] + 66
10  QuartzCore                          0x0042092d -[CALayer layoutSublayers] + 266
11  QuartzCore                          0x0042a827 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 231
12  QuartzCore                          0x003b0fa7 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 377
13  QuartzCore                          0x003b2ea6 _ZN2CA11Transaction6commitEv + 374
14  QuartzCore                          0x003b2580 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 80
15  CoreFoundation                      0x013a89ce __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
16  CoreFoundation                      0x0133f670 __CFRunLoopDoObservers + 384
17  CoreFoundation                      0x0130b4f6 __CFRunLoopRun + 1174
18  CoreFoundation                      0x0130adb4 CFRunLoopRunSpecific + 212
19  CoreFoundation                      0x0130accb CFRunLoopRunInMode + 123
20  GraphicsServices                    0x03258879 GSEventRunModal + 207
21  GraphicsServices                    0x0325893e GSEventRun + 114
22  UIKit                               0x00660a9b UIApplicationMain + 1175
23  MyApp                               0x000023f9 main + 169
24  MyApp                               0x00002345 start + 53

异常(exception)是:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance 0x146acd8'

info symbol 0x146acd8
__kCFNull in section LC_SEGMENT.__DATA.__data of /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.0.sdk/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation

第二种情况类似。然而，异常(exception)情况是完全相同的。这是调用堆栈:

0   CoreFoundation                      0x013d406e __exceptionPreprocess + 206
1   libobjc.A.dylib                     0x019f0d0a objc_exception_throw + 44
2   CoreFoundation                      0x013d5ced -[NSObject doesNotRecognizeSelector:] + 253
3   CoreFoundation                      0x0133af00 ___forwarding___ + 432
4   CoreFoundation                      0x0133ace2 _CF_forwarding_prep_0 + 50
5   UIKit                               0x0086e851 -[UIButton layoutSubviews] + 1294
6   UIKit                               0x0069f322 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 178
7   CoreFoundation                      0x013d5e72 -[NSObject performSelector:withObject:] + 66
8   QuartzCore                          0x0042092d -[CALayer layoutSublayers] + 266
9   QuartzCore                          0x0042a827 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 231
10  QuartzCore                          0x003b0fa7 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 377
11  QuartzCore                          0x003b2ea6 _ZN2CA11Transaction6commitEv + 374
12  QuartzCore                          0x003b2580 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 80
13  CoreFoundation                      0x013a89ce __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
14  CoreFoundation                      0x0133f670 __CFRunLoopDoObservers + 384
15  CoreFoundation                      0x0130b4f6 __CFRunLoopRun + 1174
16  CoreFoundation                      0x0130adb4 CFRunLoopRunSpecific + 212
17  CoreFoundation                      0x0130accb CFRunLoopRunInMode + 123
18  GraphicsServices                    0x03258879 GSEventRunModal + 207
19  GraphicsServices                    0x0325893e GSEventRun + 114
20  UIKit                               0x00660a9b UIApplicationMain + 1175
21  MyApp                               0x000023f9 main + 169
22  MyApp                               0x00002345 start + 53

Answer 1

从异常来看，您似乎认为您正在将 NSString 传递给按钮的标题，而实际上您正在传递 NSNull 的实例。如果您从 JSON 源或类似源派生 TableView 数据，则这种情况很常见 - 如果源字段不存在，则使用 NSNull。

您得到的异常(exception)是 length 不是 NSNull 的可识别选择器，这是事实，并且当按钮布局其 subview 时(当您分配新标题时它会这样做)，它似乎会出现。因此，我会将您的调查重点放在该领域。检查您实际发送的按钮标题的内容。