Question

我对KVO比较陌生，所以我很有可能违反了一些基本规则。我正在使用Core Data。

我的应用程序崩溃时出现以下消息：而我无法理解的是CGImage参与观察MeasurementPointer对象上设置的值的原因。

        *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '<CGImage 0x276fc0>: An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: measurementDescriptor
Observed object: <MeasurementPointer: 0x8201640> (entity: MeasurementPointer; id: 0x8200410 <x-coredata://EBEE0687-D67D-4B03-8C95-F4C60CFDC20F/MeasurementPointer/p75> ; data: {
    measurementDescriptor = "0x260fd0 <x-coredata://EBEE0687-D67D-4B03-8C95-F4C60CFDC20F/MeasurementDescriptor/p22>";
})
Change: {
    kind = 1;
    new = "<MeasurementDescriptor: 0x262530> (entity: MeasurementDescriptor; id: 0x260fd0 <x-coredata://EBEE0687-D67D-4B03-8C95-F4C60CFDC20F/MeasurementDescriptor/p22> ; data: {\n    measurementName = Temperature;\n    measurementUnits = \"\\U00b0C\";\n    sortString = nil;\n})";
}
Context: 0x0'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x30897ed3 __exceptionPreprocess + 114
    1   libobjc.A.dylib                     0x3002f811 objc_exception_throw + 24
    2   CoreFoundation                      0x30897d15 +[NSException raise:format:arguments:] + 68
    3   CoreFoundation                      0x30897d4f +[NSException raise:format:] + 34
    4   Foundation                          0x34a13779 -[NSObject(NSKeyValueObserving) observeValueForKeyPath:ofObject:change:context:] + 60
    5   Foundation                          0x349b6acd NSKeyValueNotifyObserver + 216
    6   Foundation                          0x349b6775 NSKeyValueDidChange + 236
    7   Foundation                          0x349ae489 -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 76
    8   CoreData                            0x3165b577 _PF_ManagedObject_DidChangeValueForKeyIndex + 102
    9   CoreData                            0x3165ac51 _sharedIMPL_setvfk_core + 184
    10  CoreData                            0x3165dc83 _svfk_0 + 10
    11  SPARKvue                            0x000479f1 -[MeasurementViewController doneAction:] + 152
    12  CoreFoundation                      0x3083f719 -[NSObject(NSObject) performSelector:withObject:withObject:] + 24
    13  UIKit                               0x31eb1141 -[UIApplication sendAction:to:from:forEvent:] + 84
    14  UIKit                               0x31f08315 -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 92
    15  CoreFoundation                      0x3083f719 -[NSObject(NSObject) performSelector:withObject:withObject:] + 24
    16  UIKit                               0x31eb1141 -[UIApplication sendAction:to:from:forEvent:] + 84
    17  UIKit                               0x31eb10e1 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 32
    18  UIKit                               0x31eb10b3 -[UIControl sendAction:to:forEvent:] + 38
    19  UIKit                               0x31eb0e05 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 356
    20  UIKit                               0x31eb1453 -[UIControl touchesEnded:withEvent:] + 342
    21  UIKit                               0x31eafddd -[UIWindow _sendTouchesForEvent:] + 368
    22  UIKit                               0x31eaf757 -[UIWindow sendEvent:] + 262
    23  UIKit                               0x31eaa9ff -[UIApplication sendEvent:] + 298
    24  UIKit                               0x31eaa337 _UIApplicationHandleEvent + 5110
    25  GraphicsServices                    0x31e4504b PurpleEventCallback + 666
    26  CoreFoundation                      0x3082cce3 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 26
    27  CoreFoundation                      0x3082cca7 __CFRunLoopDoSource1 + 166
    28  CoreFoundation                      0x3081f56d __CFRunLoopRun + 520
    29  CoreFoundation                      0x3081f277 CFRunLoopRunSpecific + 230
    30  CoreFoundation                      0x3081f17f CFRunLoopRunInMode + 58
    31  GraphicsServices                    0x31e445f3 GSEventRunModal + 114
    32  GraphicsServices                    0x31e4469f GSEventRun + 62
    33  UIKit                               0x31e51123 -[UIApplication _run] + 402
    34  UIKit                               0x31e4f12f UIApplicationMain + 670
    35  SPARKvue                            0x000031ff main + 70
    36  SPARKvue                            0x000031b4 start + 40
)
terminate called after throwing an instance of 'NSException'
Program received signal:  “SIGABRT”.

触发这一切的所有事情是：

[[self measurementPointer] setMeasurementDescriptor:descriptor];

鉴于此，

[[meterDisplay measurementPointer] addObserver:self 
            forKeyPath:@"measurementDescriptor"
            options:NSKeyValueObservingOptionNew
            context:nil];

基本上，MeasurementPointer对象指向MeasurementDescriptor对象 - 两者都是NSManagedObject子类。 MeasurementDescriptor对象描述特定的“测量”和“单位”组合（例如，“温度（°C）”或“风速（mph）”）。 MeasurementDescriptors就像单身一样，只有每个独特的测量单元组合只有一个。

MeasurementPointers由其他对象引用 - 包括Model对象和Controller对象。 MeasurementPointer引用MeasurementDescriptor。许多对象都想知道MeasurementPointer何时开始引用新的/不同的MeasurementDescriptor。例如，这种改变可能导致图形显示的轴发生变化。或者，在上面的代码中，可能会导致仪表显示显示不同的样本（来自选定的一组样本）。

我认为基本问题是CGImage正在接收不适合它的消息......不幸的是，这是间歇性的，所以我无法找到触发它的模式。

Answer 1

你有一个被释放的物体，并没有停止观察另一个物体。完成所有-addObserver...次来电，并确保它们至少在-removeObserver...和-dealloc中与-viewDidUnload次来电匹配，具体取决于您的申请结构。

Answer 2

当我将observeValueForKeyPath方法发送到super时，我看到了这个错误，我没有注册为更改的观察者。 Apple docs说“确保调用超类的[observeValueForKeyPath] 实现，如果它实现它。”

我的解决方法是改变：

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
  if ([keyPath isEqualToString:kPropertyThatChanges]) {
    ...
  }
  [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}

为：

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
  if ([keyPath isEqualToString:kPropertyThatChanges]) {
    ...
  }
}

Answer 3

我不小心将目标作为观察者（而不是自己）传递给了这个问题：

[self.someView addObserver:self.someView forKeyPath:@"key" options:0 context:nil];

错误信息对于识别这一点并没有任何帮助，所以我想发布以防其他人做同样的事情。

Answer 4

我遇到了同样的问题，但就我而言，我正在观察不同的背景。然后我将所有内容放在同一个上下文中，崩溃就消失了。我希望这有助于某人。

Answer 5

对我来说，我忘了添加override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?)来对被观察到的keyPath进行实际操作。

这是Swift版本的示例。在viewDidLoad中添加观察者，并在deinit中将其删除：

lazy var firstNameTextField: UITextField = {
    let textField = UITextField()
    // configure your textField
    return textField
}()

lazy var lastNameTextField: UITextField = {
    let textField = UITextField()
    // configure your textField
    return textField
}()

override func viewDidLoad() {
    super.viewDidLoad()

    // 1. add your observers here
    firstNameTextField.addObserver(self, forKeyPath: "text", options: [.old, .new], context: nil)
    lastNameTextField.addObserver(self, forKeyPath: "text", options: [.old, .new], context: nil)
}

// 2. ***IMPORTANT you must add this function or it will crash***
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {

    if keyPath == "text" {
        print("do something when the textField's text your observing changes")
    }
}

 // 3. remove them in deinit
deinit {
    firstNameTextField.removeObserver(self, forKeyPath: "text", context: nil)
    lastNameTextField.removeObserver(self, forKeyPath: "text", context: nil)
    print("DEINIT")
}

-observeValueForKeyPath：ofObject：change：context：收到消息但未处理

5 个答案: