Question

我需要扫描条形码，如果用户可以看到他的目标，这显然会更好一些。虽然我明确将后置摄像头设置为捕捉设备，但我的表面始终可以启用前置摄像头。

我调试了它，它实际上选择了后置摄像头，将它的id提供给MediaCapture对象进行初始化但最终无效。

var cameraDevices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture);
var backfacing =
    cameraDevices.FirstOrDefault(c => c.EnclosureLocation.Panel == Panel.Back);

var preferred = backfacing ?? cameraDevices.FirstOrDefault();
// TODO: Change into UI feedback instead
if (preferred == null) throw new Exception("No camera available.");

_capture = new MediaCapture();
_capture.Failed += CaptureOnFailed;
_capture.RecordLimitationExceeded += CaptureOnRecordLimitationExceeded;

try
{
    await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
    {
        _request = new DisplayRequest();
        _request.RequestActive();
        DisplayInformation.AutoRotationPreferences = DisplayOrientations.Landscape;
    });

    await _capture.InitializeAsync(
        new MediaCaptureInitializationSettings()
        {
            VideoDeviceId = preferred.Id,
            SourceGroup = selectedGroup,
            MemoryPreference = MediaCaptureMemoryPreference.Cpu,
            StreamingCaptureMode = StreamingCaptureMode.Video
        });

    var colorFrameSource = _capture.FrameSources[colorInfo.Id];
    var preferredFormat = colorFrameSource.SupportedFormats.FirstOrDefault(format => format.VideoFormat.Width >= 720);

    if (preferredFormat == null)
    {
        throw new Exception("Format not supported.");
    }

    await colorFrameSource.SetFormatAsync(preferredFormat);

    _frameReader = await _capture.CreateFrameReaderAsync(colorFrameSource);
    _frameReader.FrameArrived += FrameReaderOnFrameArrived;
    await _frameReader.StartAsync();
}
catch (UnauthorizedAccessException)
{
    // No permission for camera usage
}
catch (Exception ex)
{
    Debugger.Break();
}

为什么这样？我该怎么做才能改变它？我没有找到有关此事的任何信息。

Answer 1

您只需通过以下代码行选择设备前面板上的摄像头：

var backfacing = cameraDevices.FirstOrDefault(c => c.EnclosureLocation.Panel == Panel.Front);

因此它使用前置摄像头。如果您想使用后面板上的相机，则应将EnclosureLocation.Panel属性设置为Windows.Devices.Enumeration.Panel.Back

var frameSourceGroups = await MediaFrameSourceGroup.FindAllAsync();
var selectedGroupObjects = frameSourceGroups.Select(group =>
new
{
    sourceGroup = group,
    colorSourceInfo = group.SourceInfos.FirstOrDefault((sourceInfo) =>
    {
        return sourceInfo.MediaStreamType == MediaStreamType.VideoPreview
        && sourceInfo.SourceKind == MediaFrameSourceKind.Color
        && sourceInfo.DeviceInformation?.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Back;
    })
}).Where(t => t.colorSourceInfo != null)
.FirstOrDefault();

详细信息请参考official sample，它提供了可以很好地使用前后相机的样本。

UWP应用程序始终使用前置摄像头

1 个答案: