Windows Phone camera App crash when switching to another page

Question

I am creating a Simple Face Detection App for Windows Phone in C#. I turn on my camera , everything works perfect and FaceDetector works too, but when I try to navigate to other page my App always crashes and I do not why. I tried to test my App in Windows
Phone Emulator and here the navigation works. I also tried debug my App in real device, but there the method OnNavigatedFrom is never hit.
FaceDetection.xaml.cs
public partial class FaceDetection : PhoneApplicationPage
#region member variables
const string MODEL_FILE = "models/haarcascade_frontalface_alt.xml";
FaceDetector.Detector _detector;
int _downsampleFactor = 2;
private byte[] _pixelDataGray;
private byte[] _pixelDataDownsampled;
private int[] _pixelDataGrayInt;
private WriteableBitmap _wb;
private DateTime _lastUpdate;
public static int pocet = 5;
double point1;
double point2;
double heightRectangle;
double widthRectangle;
#endregion
public FaceDetection()
InitializeComponent();
_detector = new FaceDetector.Detector(XDocument.Load(MODEL_FILE));
private void NewCameraFrame(object sender, CameraFrameEventArgs cameraFrameEventArgs)
PageOrientation orientaciaObrazovky = ((PhoneApplicationFrame)Application.Current.RootVisual).Orientation;
cameraViewer.UpdateOrientation(orientaciaObrazovky);
var w = cameraViewer.CameraWidth;
var h = cameraViewer.CameraHeight;
if (_pixelDataGray == null || _pixelDataGray.Length != h * w)
_pixelDataGray = new byte[w / _downsampleFactor * h / _downsampleFactor];
_pixelDataDownsampled =
new byte[w / _downsampleFactor * h / _downsampleFactor];
_pixelDataGrayInt = new int[w / _downsampleFactor * h / _downsampleFactor];
_wb = new WriteableBitmap(w / _downsampleFactor, w / _downsampleFactor);
_lastUpdate = DateTime.Now;
Utils.DownSample(cameraFrameEventArgs.ARGBData, w, h, ref _pixelDataGrayInt, _downsampleFactor);
Utils.ARGBToGreyScale(_pixelDataGrayInt, ref _pixelDataGray);
Utils.HistogramEqualization(ref _pixelDataGray);
Utils.GrayToARGB(_pixelDataGray, ref _pixelDataGrayInt);
List<FaceDetector.Rectangle> faces = new List<FaceDetector.Rectangle>();
if (orientaciaObrazovky == PageOrientation.PortraitUp || orientaciaObrazovky == PageOrientation.PortraitDown)
int scalw = w / _downsampleFactor;
int scalh = h / _downsampleFactor;
int[] _pixelDataGrayIntRotated = new int[scalw * scalh];
for (int x = 0; x < scalw; x++)
for (int y = 0; y < scalh; y++)
_pixelDataGrayIntRotated[y + x * scalh] = _pixelDataGrayInt[x + y * scalw];
faces = _detector.getFaces(
_pixelDataGrayIntRotated,
h / _downsampleFactor,
w / _downsampleFactor,
2f, 1.25f, 0.1f, 1, false, false); // height-width swapped
else
faces = _detector.getFaces(
_pixelDataGrayInt,
w / _downsampleFactor,
h / _downsampleFactor,
2f, 1.25f, 0.1f, 1, false, false);
var elapsed = (DateTime.Now - _lastUpdate).TotalMilliseconds;
_pixelDataGrayInt.CopyTo(_wb.Pixels, 0);
_wb.Invalidate();
Dispatcher.BeginInvoke(delegate()
cnvsFaceRegions.Children.Clear();
foreach (var r in faces)
System.Windows.Shapes.Rectangle toAdd = new System.Windows.Shapes.Rectangle();
TranslateTransform loc = new TranslateTransform();
if (orientaciaObrazovky == PageOrientation.PortraitUp)
loc.X = r.X * _downsampleFactor / (double)w * cnvsFaceRegions.ActualWidth;
loc.Y = r.Y * _downsampleFactor / (double)w * cnvsFaceRegions.ActualHeight;
point1 = r.X;
point2 = r.Y;
else if (orientaciaObrazovky == PageOrientation.PortraitDown)
loc.X = r.X * _downsampleFactor / (double)w * cnvsFaceRegions.ActualWidth;
loc.Y = r.Y * _downsampleFactor / (double)w * cnvsFaceRegions.ActualHeight;
point1 = r.X;
point2 = r.Y;
else if (orientaciaObrazovky == PageOrientation.LandscapeLeft)
loc.X = r.X * _downsampleFactor / (double)w * cnvsFaceRegions.ActualWidth - 50;
loc.Y = r.Y * _downsampleFactor / (double)w * cnvsFaceRegions.ActualHeight + 90;
point1 = r.X;
point2 = r.Y;
else if (orientaciaObrazovky == PageOrientation.LandscapeRight)
loc.X = r.X * _downsampleFactor / (double)w * cnvsFaceRegions.ActualWidth+50 ;
loc.Y = r.Y * _downsampleFactor / (double)w * cnvsFaceRegions.ActualHeight -90;
point1 = r.X;
point2 = r.Y;
toAdd.RenderTransform = loc;
toAdd.Width = r.Width * _downsampleFactor + 50;
toAdd.Height = r.Height * _downsampleFactor + 50;
toAdd.Stroke = new SolidColorBrush(Colors.Red);
cnvsFaceRegions.Children.Add(toAdd);
widthRectangle = toAdd.Width;
heightRectangle = toAdd.Height;
point1 = (loc.X);
point2 = (loc.Y);
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
base.OnNavigatedTo(e);
cameraViewer.SaveToCameraRoll = true;
cameraViewer.NewCameraFrame += NewCameraFrame;
cameraViewer.StartPumpingFrames();
CameraButtons.ShutterKeyHalfPressed += OnButtonHalfPress;
CameraButtons.ShutterKeyPressed += OnButtonFullPress;
CameraButtons.ShutterKeyReleased += OnButtonRelease;
protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)
base.OnNavigatedFrom(e);
cameraViewer.StopPumpingFrames();
CameraButtons.ShutterKeyHalfPressed -= OnButtonHalfPress;
CameraButtons.ShutterKeyPressed -= OnButtonFullPress;
CameraButtons.ShutterKeyReleased -= OnButtonRelease;
private void OnButtonHalfPress(object sender, EventArgs e)
cameraViewer.NewCameraFrame -= NewCameraFrame;
private void OnButtonFullPress(object sender, EventArgs e)
SaveScreenShots();
private void OnButtonRelease(object sender, EventArgs e)
cameraViewer.NewCameraFrame += NewCameraFrame;
private static WriteableBitmap CropImage(WriteableBitmap source, int xOffset, int yOffset, int width, int height)
var sourceWidth = source.PixelWidth;
var result = new WriteableBitmap(width, height);
for (var x = 0; x <= height - 1; x++)
var sourceIndex = xOffset + (yOffset + x) * sourceWidth;
var destinationIndex = x * width;
Array.Copy(source.Pixels, sourceIndex, result.Pixels, destinationIndex, width);
return result;
private void SaveScreenShots()
string namePerson = PhoneApplicationService.Current.State["TextBoxValue"] as String;
bool b = cnvsFaceRegions.Children.Any();
cnvsFaceRegions.Children.Clear();
if (!b)
MessageBox.Show("No face detected ");
else
for (int j = 1; j <= pocet; j++)
using (var isoStore = IsolatedStorageFile.GetUserStoreForApplication())
var bmp = new WriteableBitmap((int)this.ActualWidth, (int)this.ActualHeight);
bmp.Render(this, null);
byte[] bb = EncodeToJpeg(bmp);
bmp.Invalidate();
WriteableBitmap bmp2 = CropImage(bmp, (int)point1, (int)point2, (int)widthRectangle, (int)heightRectangle);
using (var isoFileStream = isoStore.CreateFile(namePerson + j))
System.Windows.Media.Imaging.Extensions.SaveJpeg(bmp2, isoFileStream, bmp.PixelWidth, bmp.PixelHeight, 0, 100);
isoFileStream.Close();
MessageBox.Show("Saved successfully " + pocet + " images");
cameraViewer.NewCameraFrame += NewCameraFrame;
public byte[] EncodeToJpeg(WriteableBitmap wb)
using (MemoryStream stream = new MemoryStream())
wb.SaveJpeg(
stream,
wb.PixelWidth,
wb.PixelHeight,
0,
85);
return stream.ToArray();
private void cameraViewer_MouseLeftButtonDown_1(object sender, MouseButtonEventArgs e)
cameraViewer.NewCameraFrame -= NewCameraFrame;
private void cameraViewer_MouseLeftButtonUp_1(object sender, MouseButtonEventArgs e)
SaveScreenShots();
private void ApplicationBarMenuItem_Click(object sender, EventArgs e)
NavigationService.Navigate(new Uri("/PersonAndGallery;component/Gallery.xaml", UriKind.Relative));
CameraViewer.cs
public class CameraFrameEventArgs : RoutedEventArgs
public int[] ARGBData { get; set; }
public static class AppGlobal
public static bool isPortrait = true;
public class CameraViewer : Grid
#region Events
public EventHandler<CameraFrameEventArgs> NewCameraFrame { get; set; }
public EventHandler<ContentReadyEventArgs> NewCameraCaptureImage { get; set; }
public EventHandler<CameraOperationCompletedEventArgs> CamInitialized { get; set; }
#endregion
#region Properties
public int CameraWidth
get { return _cameraWidth; }
set { _cameraWidth = value; }
public int CameraHeight
get { return _cameraHeight; }
set { _cameraHeight = value; }
public bool PhotoOnPress
get { return _photoOnPress; }
set
_photoOnPress = value;
// CameraButtons.ShutterKeyPressed -= CameraButtonsOnShutterKeyPressed;
if (_photoOnPress)
// CameraButtons.ShutterKeyPressed += CameraButtonsOnShutterKeyPressed;
public bool SaveToCameraRoll { get; set; }
public PhotoCamera Camera
get { return _camera; }
public bool TakingPhoto
get { return _takingPhoto; }
#endregion
#region Member Variables
private PhotoCamera _camera; // the windows phone camera that takes the photos
private int _cameraWidth = -1;
private int _cameraHeight = -1;
private Thread _pumpFramesThread;
private static ManualResetEvent _pauseFramesEvent = new ManualResetEvent(true);
private bool _takingPhoto;
VideoBrush viewfinderBrush;
private bool _photoOnPress;
private SoundEffect _cameraShutterSound;
private static ManualResetEvent _cameraCaptureEvent = new ManualResetEvent(true);
private static ManualResetEvent _cameraInitializedEvent = new ManualResetEvent(false);
private bool _pumpFrames;
#endregion
#region Constructor
public CameraViewer()
Unloaded += new RoutedEventHandler(OnUnloaded);
PhotoOnPress = true;
public override void OnApplyTemplate()
base.OnApplyTemplate();
#endregion
#region Public methods
public void StartPumpingFrames()
_pauseFramesEvent = new ManualResetEvent(true);
_cameraCaptureEvent = new ManualResetEvent(true);
_cameraInitializedEvent = new ManualResetEvent(false);
InitializeCamera();
_pumpFrames = true;
if (_pumpFramesThread == null)
_pumpFramesThread = new Thread(PumpFrames);
if (!_pumpFramesThread.IsAlive)
_pumpFramesThread.Start();
public void StopPumpingFrames()
_pumpFrames = false;
_pumpFramesThread = null;
Camera.Dispose();
public void TakePhoto()
if (TakingPhoto)
return;
_cameraCaptureEvent.Reset();
FrameworkDispatcher.Update();
_cameraShutterSound.Play();
_takingPhoto = true;
Camera.CaptureImage();
#endregion
private void CameraButtonsOnShutterKeyPressed(object sender, EventArgs eventArgs)
if (_photoOnPress && !TakingPhoto)
_cameraCaptureEvent.WaitOne();
TakePhoto();
private void OnUnloaded(object sender, RoutedEventArgs e)
_cameraInitializedEvent.Reset();
public void InitializeCamera()
_cameraInitializedEvent.Reset();
// Check to see if the camera is available on the device.
if ((PhotoCamera.IsCameraTypeSupported(CameraType.Primary) == true) ||
(PhotoCamera.IsCameraTypeSupported(CameraType.FrontFacing) == true))
// Initialize the default camera.
_camera = new Microsoft.Devices.PhotoCamera();
//Event is fired when the PhotoCamera object has been initialized
Camera.Initialized +=
new EventHandler<Microsoft.Devices.CameraOperationCompletedEventArgs>(CameraInitialized);
Camera.CaptureImageAvailable += CameraOnCaptureImageAvailable;
Camera.CaptureCompleted += CameraOnCaptureCompleted;
//Set the VideoBrush source to the camera
// var viewfinderBrush = new VideoBrush();
viewfinderBrush = new VideoBrush();
viewfinderBrush.Stretch = Stretch.Fill;
viewfinderBrush.RelativeTransform = new CompositeTransform { CenterX = 0.5, CenterY = 0.5 };
viewfinderBrush.SetSource(Camera);
System.Windows.Shapes.Rectangle rect = new System.Windows.Shapes.Rectangle();
rect.Fill = viewfinderBrush;
this.Children.Add(rect);
Stream stream = TitleContainer.OpenStream("models/shutter.wav");
_cameraShutterSound = SoundEffect.FromStream(stream);
// CameraButtons.ShutterKeyPressed -= CameraButtonsOnShutterKeyPressed;
if (_photoOnPress)
// CameraButtons.ShutterKeyPressed += CameraButtonsOnShutterKeyPressed;
else
// The camera is not supported on the device.
MessageBox.Show(
"Sorry, this sample requires a phone camera and no camera is detected. This application will not show any camera output.");
private void CameraOnCaptureCompleted(object sender, CameraOperationCompletedEventArgs cameraOperationCompletedEventArgs)
_cameraCaptureEvent.Set();
_takingPhoto = false;
private void CameraOnCaptureImageAvailable(object sender, ContentReadyEventArgs contentReadyEventArgs)
if (SaveToCameraRoll)
Dispatcher.BeginInvoke(() =>
WriteableBitmap bitmap =
CreateWriteableBitmap(contentReadyEventArgs.ImageStream,
(int)Camera.Resolution.Width,
(int)Camera.Resolution.Height);
// SaveCapturedImage(bitmap);
//TakeScreenShots();
if (NewCameraCaptureImage != null)
NewCameraCaptureImage.Invoke(this, contentReadyEventArgs);
// Helper for CameraOnCaptureImageAvailable
private void SaveCapturedImage(WriteableBitmap imageToSave)
var stream = new MemoryStream();
imageToSave.SaveJpeg(stream, imageToSave.PixelWidth, imageToSave.PixelHeight, 0, 100);
//Take the stream back to its beginning because it will be read again
//when saving to the library
stream.Position = 0;
var library = new MediaLibrary();
string fileName = string.Format("{0:yyyy-MM-dd-HH-mm-ss}.jpg", DateTime.Now);
library.SavePictureToCameraRoll(fileName, stream);
//save to Save Photo
Picture pic;
private void TakeScreenShots()
WriteableBitmap bmp = new WriteableBitmap((int)this.ActualWidth, (int)this.ActualHeight);
bmp.Render(this, null);
byte[] bb = EncodeToJpeg(bmp);
bmp.Invalidate();
MemoryStream mem = new MemoryStream();
bmp.SaveJpeg(mem, bmp.PixelWidth, bmp.PixelHeight, 0, 100);
mem.Seek(0, System.IO.SeekOrigin.Begin);
if (mem != null)
MediaLibrary library = new MediaLibrary();
try
pic = library.SavePicture("Mask_" + Guid.NewGuid().ToString(), mem);
MessageBox.Show("Your picture is now accessible through the Saved Picture album.", "Saved successfully.", MessageBoxButton.OK);
catch (Exception ex)
MessageBox.Show("Unable to save the photo." + ex);
public byte[] EncodeToJpeg(WriteableBitmap wb)
using (MemoryStream stream = new MemoryStream())
wb.SaveJpeg(
stream,
wb.PixelWidth,
wb.PixelHeight,
0,
85);
return stream.ToArray();
// Creates a WriteableBitmap from an imageStream
private WriteableBitmap CreateWriteableBitmap(Stream imageStream, int width, int height)
var bitmap = new WriteableBitmap(width, height);
imageStream.Position = 0;
bitmap.LoadJpeg(imageStream);
return bitmap;
private void CameraInitialized(object sender, CameraOperationCompletedEventArgs e)
if (e.Succeeded)
try
// available resolutions are ordered based on number of pixels in each resolution
CameraWidth = (int)Camera.PreviewResolution.Width;
CameraHeight = (int)Camera.PreviewResolution.Height;
if (CamInitialized != null)
CamInitialized.Invoke(this, e);
_cameraInitializedEvent.Set();
_pauseFramesEvent.Set();
catch (ObjectDisposedException)
// If the camera was disposed, try initializing again
private void PumpFrames()
_cameraInitializedEvent.WaitOne();
int[] pixels = new int[CameraWidth * CameraHeight];
int numExceptions = 0;
while (_pumpFrames)
_pauseFramesEvent.WaitOne();
_cameraCaptureEvent.WaitOne();
_cameraInitializedEvent.WaitOne();
try
Camera.GetPreviewBufferArgb32(pixels);
catch (Exception e)
// If we get an exception try capturing again, do this up to 10 times
if (numExceptions >= 10)
throw e;
numExceptions++;
continue;
numExceptions = 0;
_pauseFramesEvent.Reset();
Deployment.Current.Dispatcher.BeginInvoke(
() =>
if (NewCameraFrame != null && _pumpFrames)
NewCameraFrame(this, new CameraFrameEventArgs { ARGBData = pixels });
_pauseFramesEvent.Set();
//na zmenu orientacie
public void UpdateOrientation(PageOrientation orientation)
if (orientation == PageOrientation.PortraitDown)
viewfinderBrush.RelativeTransform =
new CompositeTransform { CenterX = 0.5, CenterY = 0.5, Rotation = 270 };
/* else if (orientation == PageOrientation.PortraitDown && cameraType == 2)
viewfinderBrush.RelativeTransform =
new CompositeTransform { CenterX = 0.5, CenterY = 0.5, Rotation = 90 };
else if (orientation == PageOrientation.PortraitUp && cameraType == 2)
viewfinderBrush.RelativeTransform =
new CompositeTransform { CenterX = 0.5, CenterY = 0.5, Rotation = -90 };
else if (orientation == PageOrientation.PortraitUp)
viewfinderBrush.RelativeTransform =
new CompositeTransform { CenterX = 0.5, CenterY = 0.5, Rotation =90 };
else if (orientation == PageOrientation.LandscapeLeft)
viewfinderBrush.RelativeTransform =
new CompositeTransform { CenterX = 0.5, CenterY = 0.5, Rotation = 0 };
else if (orientation == PageOrientation.LandscapeRight)
viewfinderBrush.RelativeTransform =
new CompositeTransform { CenterX = 0.5, CenterY = 0.5, Rotation = -180 };
Thanks for reply.

Answer 1

Hi Facko,
Thanks for posting at the forum, however it could be really difficult for us to copy/paste your code and try to repro the issue, I would suggest you to provide a repro sample for us so that we can debug for you.
And base on your description, looks like your app only crashes on the real device, but not on the emulator. I have question here, how the app works on the emulator?
As I know if we open the camera on emulator, the only thing we can see is kind of small color blocks instead of the real images.
You could also try to close the camera and then dispose the object to see if it works.
--James
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