我有一个UITableViewCell，有2个UIButton个实例。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。没什么。
在单元格类中，这两个按钮被声明为具有IBOutlet关键字的属性：
@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的连接。
因此，当加载.xib时，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];
}
当视图控制器出现时，它会成功通过(UITableViewCell*)tableView:cellForRowAtIndexPath:所需的次数。然后应用程序崩溃了以下堆栈：
0 kill
...
[UIButton imageRectForContentRect:]
[UIButton(UIButtonInternal) _setupImageView]
[UIButton layoutSubviews]
...
start
我删除了按钮的图像并开始崩溃堆栈：
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，并且崩溃停止。但按钮不起作用。
知道导致崩溃的原因是什么？
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
例外是：
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。但是，例外是完全相同的。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
答案 0 :(得分：1)
从异常中看，您认为您正在将NSString传递给按钮的标题，并且您实际上正在传递NSNull的实例。如果要从JSON源或类似源派生表视图数据，这是很常见的 - 如果源字段不存在，则使用NSNull。
你得到的例外是长度不是NSNull的公认选择器，这是真的，并且当按钮布局其子视图时它似乎出现，当你分配新标题时它会这样做。所以我会把你的调查集中在那个领域。检查您实际发送的按钮标题。
答案 1 :(得分：0)
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;
[cell.buttonGPS addTarget:self action:@selector(actionGPS:) forControlEvents:UIControlEventTouchUpInside];
[cell.buttonCall addTarget:self action:@selector(actionCall:) forControlEvents:UIControlEventTouchUpInside];
}
// gps button
[cell.buttonGPS setTitle:[NSString stringWithFormat:@"%d", indexPath.row] forState:UIControlStateNormal];
if (...condition...)
{
cell.buttonCall.enabled = NO;
}
else
{
cell.buttonCall.enabled = YES;
[cell.buttonCall setTitle:[...TheTitleString...] forState:UIControlStateNormal];
}
在你的代码中进行这些更改＆amp;校验。我认为某些条件可能是错误的，所以b4添加目标它已被删除，并在尝试时它崩溃。