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Fix Windows unexpected exceptions in multi-page applications. #146

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Fix Windows unexpected exceptions in multi-page applications. #146

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2a2a48a
Fix unexpected win32 exceptions when unloading the _cameraPreview con…
paoldev Oct 29, 2023
af2a8ed
Automatically restart the camera when reloading _cameraPreview contro…
paoldev Oct 29, 2023
f6c4002
Fix formatting
paoldev Oct 29, 2023
1ea12ac
Merge branch 'Redth:main' into FixMultiPage
paoldev Sep 29, 2024
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157 changes: 110 additions & 47 deletions ZXing.Net.MAUI/Platforms/Windows/CameraManager.windows.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -77,8 +77,11 @@ internal partial class CameraManager
//Active camera properties
string _currentMediaFrameSourceGroupId;
string _currentMediaFrameSourceInfoId;
string _lastUnloadedMediaFrameSourceGroupId = null;
private SoftwareBitmap _backBuffer;
private bool _taskRunning = false;
private volatile bool _taskRunning = false;
private volatile bool _colorFrameReaderHandlerRunning = false;
private volatile bool _colorFrameReaderHandlerAvailable = false;
private readonly DispatcherQueue _dispatcherQueueUI = DispatcherQueue.GetForCurrentThread();

//MediaCapture
Expand Down Expand Up @@ -163,6 +166,7 @@ public NativePlatformCameraPreviewView CreateNativeView()
//See https://learn.microsoft.com/en-us/dotnet/maui/user-interface/handlers/create#native-view-cleanup
//for an explanation of DisconnectHandler() behaviour.
_cameraPreview.Unloaded += CameraPreview_Unloaded;
_cameraPreview.Loaded += CameraPreview_Loaded;
}
return _cameraPreview;
}
Expand Down Expand Up @@ -214,6 +218,9 @@ private async Task ConnectAsync()
{
await ExecuteLockedAsync(async () =>
{
//Connecting: forget any previously unloaded camera.
_lastUnloadedMediaFrameSourceGroupId = null;

await InitCameraUnlockedAsync();

#if ENABLE_DEVICE_WATCHER
Expand All @@ -226,6 +233,9 @@ private async Task DisconnectAsync()
{
await ExecuteLockedAsync(async () =>
{
//Disconnecting: forget any previously unloaded camera.
_lastUnloadedMediaFrameSourceGroupId = null;

#if ENABLE_DEVICE_WATCHER
UnregisterWatcher(this);
#endif
Expand All @@ -239,6 +249,12 @@ private async Task UpdateCameraAsync(string sourceGroupId = null)
{
await ExecuteLockedAsync(async () =>
{
if (!string.IsNullOrEmpty(_lastUnloadedMediaFrameSourceGroupId) && _lastUnloadedMediaFrameSourceGroupId.Equals(sourceGroupId))
{
//This cameraManager will be initialized in CameraPreview_Loaded handler.
return;
}

await InitCameraUnlockedAsync(sourceGroupId);
});
}
Expand Down Expand Up @@ -354,6 +370,7 @@ private async Task InitCameraUnlockedAsync(string sourceGroupId = null)
#else
_mediaFrameReader = await _mediaCapture.CreateFrameReaderAsync(selectedMediaFrameSource, MediaEncodingSubtypes.Bgra8);
#endif
_colorFrameReaderHandlerAvailable = true;
_mediaFrameReader.FrameArrived += ColorFrameReader_FrameArrived;
await _mediaFrameReader.StartAsync();

Expand All @@ -375,6 +392,7 @@ private async Task UninitCameraUnlockedAsync(string sourceGroupId = null)
{
if (_mediaFrameReader != null)
{
_colorFrameReaderHandlerAvailable = false;
await _mediaFrameReader.StopAsync();
_mediaFrameReader.FrameArrived -= ColorFrameReader_FrameArrived;
_mediaFrameReader.Dispose();
Expand All @@ -388,6 +406,20 @@ private async Task UninitCameraUnlockedAsync(string sourceGroupId = null)
}
_currentMediaFrameSourceInfoId = null;
_currentMediaFrameSourceGroupId = null;
//Wait for and flush any pending 'ColorFrameReader_FrameArrived' event.
while (_colorFrameReaderHandlerRunning || _taskRunning)
{
await Task.Delay(1);
}
//Detach any valid SoftwareBitmap from imageSource, to avoid random and unexpected win32 exceptions
//(such as 0xC000027B) when recreating the camera manager, after unloading and reloading the _cameraPreview control.
//The crash may happen in multipage applications, such as those based upon Shell layout.
_backBuffer?.Dispose();
_backBuffer = null;
{
var imageSource = _imageElement?.Source as SoftwareBitmapSource;
await imageSource?.SetBitmapAsync(null);
}
HidePreviewBitmap();
}
}
Expand Down Expand Up @@ -624,14 +656,31 @@ private void ShowPreviewBitmap()
#endif
_imageElement.Visibility = Microsoft.UI.Xaml.Visibility.Visible;
}
#endregion
#endregion

#region Event handlers
//Hack to call Disconnect() when closing the CameraManager owner, because,
//currently, DisconnectHandler() is not automatically called by Maui framework.
#region Event handlers
//Cleanup all camera resources when unloading the _cameraPreview element,
//otherwise the camera stream continuously generates frames also when this camera
//is temporarily hidden, for example when switching pages in Shell-based applications.
//Note: this handler is needed since DisconnectHandler() is not automatically called by
//Maui framework when closing the page owning this camera.
//See https://learn.microsoft.com/en-us/dotnet/maui/user-interface/handlers/create#native-view-cleanup
private void CameraPreview_Unloaded(object sender, Microsoft.UI.Xaml.RoutedEventArgs e)
{
Disconnect();
//Use CleanupCameraAsync instead of Disconnect to keep the DeviceWatcher alive. Only DisconnectHandler()
//will call Disconnect() to also detach the DeviceWatcher.
_lastUnloadedMediaFrameSourceGroupId = _currentMediaFrameSourceGroupId;
TryEnqueueUI(async () => await CleanupCameraAsync());
}

private void CameraPreview_Loaded(object sender, Microsoft.UI.Xaml.RoutedEventArgs e)
{
if (!string.IsNullOrEmpty(_lastUnloadedMediaFrameSourceGroupId))
{
string sourceGroupId = _lastUnloadedMediaFrameSourceGroupId;
_lastUnloadedMediaFrameSourceGroupId = null;
TryEnqueueUI(async () => await UpdateCameraAsync(sourceGroupId));
}
}

//Reset the camera in case of errors
Expand All @@ -645,56 +694,70 @@ private void MediaCapture_Failed(MediaCapture sender, MediaCaptureFailedEventArg
//Display the captured frame and send it to the registered FrameReady owner.
private void ColorFrameReader_FrameArrived(MediaFrameReader sender, MediaFrameArrivedEventArgs args)
{
var mediaFrameReference = sender.TryAcquireLatestFrame();
var videoMediaFrame = mediaFrameReference?.VideoMediaFrame;
var softwareBitmap = videoMediaFrame?.SoftwareBitmap;

if (softwareBitmap != null)
if (_colorFrameReaderHandlerAvailable)
{
//Convert to Bgra8 Premultiplied softwareBitmap.
if (softwareBitmap.BitmapPixelFormat != Windows.Graphics.Imaging.BitmapPixelFormat.Bgra8 ||
softwareBitmap.BitmapAlphaMode != Windows.Graphics.Imaging.BitmapAlphaMode.Premultiplied)
{
softwareBitmap = SoftwareBitmap.Convert(softwareBitmap, BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied);
}
_colorFrameReaderHandlerRunning = true;

//Send bitmap to BarCodeReaderView/CameraView
FrameReady?.Invoke(this, new CameraFrameBufferEventArgs(
new Readers.PixelBufferHolder
{
Data = softwareBitmap,
Size = new Microsoft.Maui.Graphics.Size(softwareBitmap.PixelWidth, softwareBitmap.PixelHeight)
}));

// Swap the processed frame to _backBuffer and dispose of the unused image.
softwareBitmap = Interlocked.Exchange(ref _backBuffer, softwareBitmap);
softwareBitmap?.Dispose();
try
{
var mediaFrameReference = sender.TryAcquireLatestFrame();
var videoMediaFrame = mediaFrameReference?.VideoMediaFrame;
var softwareBitmap = videoMediaFrame?.SoftwareBitmap;

// Changes to XAML ImageElement must happen on UI thread through Dispatcher
TryEnqueueUI(
async () =>
if (softwareBitmap != null)
{
// Don't let two copies of this task run at the same time.
if (_taskRunning)
//Convert to Bgra8 Premultiplied softwareBitmap.
if (softwareBitmap.BitmapPixelFormat != Windows.Graphics.Imaging.BitmapPixelFormat.Bgra8 ||
softwareBitmap.BitmapAlphaMode != Windows.Graphics.Imaging.BitmapAlphaMode.Premultiplied)
{
return;
softwareBitmap = SoftwareBitmap.Convert(softwareBitmap, BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied);
}
_taskRunning = true;

// Keep draining frames from the backbuffer until the backbuffer is empty.
SoftwareBitmap latestBitmap;
while ((latestBitmap = Interlocked.Exchange(ref _backBuffer, null)) != null)
{
var imageSource = (SoftwareBitmapSource)_imageElement.Source;
await imageSource.SetBitmapAsync(latestBitmap);
latestBitmap.Dispose();
}
//Send bitmap to BarCodeReaderView/CameraView
FrameReady?.Invoke(this, new CameraFrameBufferEventArgs(
new Readers.PixelBufferHolder
{
Data = softwareBitmap,
Size = new Microsoft.Maui.Graphics.Size(softwareBitmap.PixelWidth, softwareBitmap.PixelHeight)
}));

_taskRunning = false;
});
}
// Swap the processed frame to _backBuffer and dispose of the unused image.
softwareBitmap = Interlocked.Exchange(ref _backBuffer, softwareBitmap);
softwareBitmap?.Dispose();

mediaFrameReference?.Dispose();
// Changes to XAML ImageElement must happen on UI thread through Dispatcher
TryEnqueueUI(
async () =>
{
// Don't let two copies of this task run at the same time.
if (_taskRunning || !_colorFrameReaderHandlerAvailable)
{
return;
}
_taskRunning = true;

// Keep draining frames from the backbuffer until the backbuffer is empty.
SoftwareBitmap latestBitmap;
while ((latestBitmap = Interlocked.Exchange(ref _backBuffer, null)) != null)
{
var imageSource = (SoftwareBitmapSource)_imageElement.Source;
await imageSource.SetBitmapAsync(latestBitmap);
latestBitmap.Dispose();
}

_taskRunning = false;
});
}

mediaFrameReference?.Dispose();
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}

_colorFrameReaderHandlerRunning = false;
}
}
#endregion

Expand Down
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