NSRangeException - 无法移除观察者

Posted 2023-02-23

【中文标题】NSRangeException - 无法移除观察者

【英文标题】：NSRangeException - cannot remove observer

【发布时间】：2015-07-31 10:32:55

【问题描述】：

我正在尝试从相机捕获图像并录制视频，但每当我用相机关闭视图时，我都会收到此错误：

由于未捕获的异常“NSRangeException”而终止应用程序，原因： '无法删除观察者 App.CameraViewController 0x16ea7f70 for 关键路径“movieFileOutput.recording”来自 App.CameraViewController 0x16ea7f70 因为它没有注册为 观察者。 *** 第一次抛出调用堆栈：（0x2a9e6fef 0x3908ac8b 0x2a9e6f35 0x2b6850f5 0x2b684b07 0x2b6849ab 0xbeb40 0xbca88 0x85c173 0x864d67 0x85ea61 0x866b09 0x867e19 0x39782dc1 0x39782b14) libc++abi.dylib: 以 NSException 类型的未捕获异常终止

我的代码：

class CameraViewController: UIViewController, CameraDelegate, AVCaptureFileOutputRecordingDelegate 

    // MARK:
    // MARK: - Property
    @IBOutlet weak var captureButton: UIButton!
    @IBOutlet var previewView: CameraPreviewView!

    weak var cameraDelegate: CameraDelegate?

    var sessionQueue: dispatch_queue_t?
    var captureSession: AVCaptureSession?
    var stillImageOutput: AVCaptureStillImageOutput?
    var videoDeviceInput: AVCaptureDeviceInput?
    var movieFileOutput: AVCaptureMovieFileOutput?

    var previewLayer: AVCaptureVideoPreviewLayer?

    var deviceAuthorized: Bool  = false
    var backgroundRecordId: UIBackgroundTaskIdentifier = UIBackgroundTaskInvalid
    var sessionRuningAndDeviceAuthorized: Bool 
        get 
            return (self.captureSession?.running != nil && self.deviceAuthorized )
        
    
    var runtimeErrorHandlingObserver: AnyObject?
...

添加观察者：

    override func viewWillAppear(animated: Bool) 
        super.viewWillAppear(animated)

        dispatch_async(self.sessionQueue!, 
            // TODO: Make constants
            self.addObserver(self, forKeyPath: "sessionRunningAndDeviceAuthorized", options: NSKeyValueObservingOptions.Old | NSKeyValueObservingOptions.New, context: &SessionRunningAndDeviceAuthorizedContext)
            self.addObserver(self, forKeyPath: "stillImageOutput.capturingStillImage", options: NSKeyValueObservingOptions.Old | NSKeyValueObservingOptions.New, context: &CapturingStillImageContext)
            self.addObserver(self, forKeyPath: "movieFileOutput.recording", options: NSKeyValueObservingOptions.Old | NSKeyValueObservingOptions.New, context: &RecordingContext)


            NSNotificationCenter.defaultCenter().addObserver(self, selector: "subjectAreaDidChange:", name: AVCaptureDeviceSubjectAreaDidChangeNotification, object: self.videoDeviceInput?.device)

            weak var weakSelf = self

            self.runtimeErrorHandlingObserver = NSNotificationCenter.defaultCenter().addObserverForName(AVCaptureSessionRuntimeErrorNotification, object: self.captureSession, queue: nil, usingBlock: 
                (note: NSNotification?) in
                var stronSelf: CameraViewController = weakSelf!
                dispatch_async(stronSelf.sessionQueue!, 
                    if let sess = stronSelf.captureSession 
                        sess.startRunning()
                    
                )

            )

            self.captureSession?.startRunning()
        )                                    
    

以及移除观察者的代码：

override func viewWillDisappear(animated: Bool) 
        super.viewWillDisappear(animated)

        dispatch_async(self.sessionQueue!, 

            if let sess = self.captureSession 
                sess.stopRunning()

                NSNotificationCenter.defaultCenter().removeObserver(self, name: AVCaptureDeviceSubjectAreaDidChangeNotification, object: self.videoDeviceInput?.device)
                NSNotificationCenter.defaultCenter().removeObserver(self.runtimeErrorHandlingObserver!)

                // TODO: Make constants

                self.removeObserver(self, forKeyPath: "sessionRunningAndDeviceAuthorized", context: &SessionRunningAndDeviceAuthorizedContext)
                self.removeObserver(self, forKeyPath: "stillImageOutput.capturingStillImage", context: &CapturingStillImageContext)
                self.removeObserver(self, forKeyPath: "movieFileOutput.recording", context: &SessionRunningAndDeviceAuthorizedContext)

            
        )
    

【参考方案1】：

你在removeObserver(...)中使用了错误的上下文

另外，你为什么要在异步块中删除观察者？