Fatal error when camera is initializing and back button is pressed or page navigating - windows-phone-7

Question

I'm working on WP7/8 application with barcode scanning. And have a problem with disposing camera. Camera initialize too long, and when camera is still initializing and I press back button, I've got a fatal error:
A first chance exception of type 'System.ObjectDisposedException'
occurred in Microsoft.Devices.Camera.ni.dll WinRT information: Fatal
error. Disposing capture device.
Could anybody helps me how to avoid this error?
my code:
protected override void OnNavigatedTo(NavigationEventArgs e)
{
InitializeAndGo();
base.OnNavigatedTo(e);
}
protected override void OnNavigatingFrom(System.Windows.Navigation.NavigatingCancelEventArgs e)
{
disposeCamera();
}
private void PhotoCameraOnInitialized(object sender, CameraOperationCompletedEventArgs cameraOperationCompletedEventArgs)
{
_width = Convert.ToInt32(_photoCamera.PreviewResolution.Width);
_height = Convert.ToInt32(_photoCamera.PreviewResolution.Height);
_luminance = new PhotoCameraLuminanceSource(_width, _height);
if (_photoCamera.IsFlashModeSupported(FlashMode.Auto))
{
_photoCamera.FlashMode = FlashMode.Off;
}
cameraInitialized = true;
Dispatcher.BeginInvoke(() =>
{
FlashCheckbox.IsEnabled = true;
if (_photoCamera.IsFlashModeSupported(FlashMode.Auto))
{
_photoCamera.FlashMode = FlashMode.Off;
}
});
_photoCamera.Focus();
}
private void InitializeAndGo()
{
stopScan = false;
_photoCamera = new PhotoCamera();
_photoCamera.Initialized += PhotoCameraOnInitialized;
_photoCamera.AutoFocusCompleted += PhotoCameraOnAutoFocusCompleted;
viewfinderBrush.SetSource(_photoCamera);
_previewTransform.Rotation = _photoCamera.Orientation;
_results = new ObservableCollection<Result>();
_barcodeReader = new BarcodeReader();
_barcodeReader.TryHarder = true;
_barcodeReader.AutoRotate = true;
_service = new MyMoviesDataService(ErrorDataService);
}
private void disposeCamera()
{
try
{
cameraInitialized = false;
StopScan();
_photoCamera.Initialized -= PhotoCameraOnInitialized;
_photoCamera.AutoFocusCompleted -= PhotoCameraOnAutoFocusCompleted;
_photoCamera.Dispose();
_photoCamera = null;
}
catch (Exception ex)
{
App.ShowErrorToast(ex.Message);
}
}

Answer 1

Don't use the camera until it's been successfully initialized (You can check this in the camera's Initialized event).
Also, wrap any usages of the camera in a
try
{
// camera code here
}
catch (ObjectDisposedException)
{
// re-initialize the camera?
}
to handle situations like suspension, which will dispose of the camera automatically.
As for the
An exception of type 'System.ObjectDisposedException' occurred in
Microsoft.Devices.Camera.ni.dll and wasn't handled before a
managed/native boundary WinRT information: Fatal error. Disposing
capture device.
This is something Microsoft needs to fix; I mean, how are you supposed to handle a native code exception if it isn't allowed to propagate to managed code?

Answer 2

Where is the exception coming from (which code line / block)?
I would for starter put a try...catch around InitializeAndGo() in the OnNavigatedTo event handler. And on the whole PhotoCameraOnInitialized event handler also.
Cheers,