Question

我的问题非常简单，我无法使用Windows Phone 8.1中的MediaCapture API打开闪光灯。（我用8.0 API成功了）

我使用2个按钮构建了一个非常简单的项目，一个用于切换FlashControl，另一个用于切换TorchControl。

没有崩溃，也没有例外。我的手机支持FlashControl和TorchControl。我也一步一步地调试，一切看起来都很好，点击按钮时值会改变。

这是我的代码：

MediaCapture m_captureManager;

public MainPage()
{
  InitializeComponent();
}

private static async Task<DeviceInformation> GetCameraID(Windows.Devices.Enumeration.Panel desiredCamera)
{
  DeviceInformation deviceID = (await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture))
      .FirstOrDefault(x => x.EnclosureLocation != null && x.EnclosureLocation.Panel == desiredCamera);
  if (deviceID != null) return deviceID;
  else throw new Exception(string.Format("Camera {0} doesn't exist", desiredCamera));
}

protected async override void OnNavigatedTo(NavigationEventArgs e)
{
  var cameraID = await GetCameraID(Windows.Devices.Enumeration.Panel.Back);
  m_captureManager = new MediaCapture();

  await m_captureManager.InitializeAsync(new MediaCaptureInitializationSettings
  {
    StreamingCaptureMode = StreamingCaptureMode.Video,
    PhotoCaptureSource = PhotoCaptureSource.VideoPreview,
    AudioDeviceId = string.Empty,
    VideoDeviceId = cameraID.Id
  });

}

private void button_ClickTorch(object sender, RoutedEventArgs e)
{
  var torch = m_captureManager.VideoDeviceController.TorchControl;
  if (torch.Supported)
  {
    if (torch.Enabled)
      torch.Enabled = false;
    else
      torch.Enabled = true;
  }
}

private void button_ClickFlash(object sender, RoutedEventArgs e)
{
  if (captureManager.VideoDeviceController.FlashControl.Supported)
  {
    if (captureManager.VideoDeviceController.FlashControl.Enabled)
      captureManager.VideoDeviceController.FlashControl.Enabled = false;
    else
      captureManager.VideoDeviceController.FlashControl.Enabled = true;
  }
}

它是一段简单的代码，我无法使其工作......我非常绝望所以我试图通过使用中间对象进行切换，但是没有，正如您所看到的，但它没有改变结果（符合要求）。

Answer 1

我终于发现了什么是错的。为了能够使用相机服务，我们必须开始预览。由于使用Silverlight我们不能使用CaptureElement，我们必须使用带有VideoBrush的CustomPreviewSink

这是怎么做的（来自microsoft doc）

private async void StartPreview()
{
previewSink = new Windows.Phone.Media.Capture.MediaCapturePreviewSink();

// List of supported video preview formats to be used by the default preview format selector.
var supportedVideoFormats = new List<string> { "nv12", "rgb32" };

// Find the supported preview format
var availableMediaStreamProperties = mediaCaptureManager.VideoDeviceController.GetAvailableMediaStreamProperties(
    Windows.Media.Capture.MediaStreamType.VideoPreview)
        .OfType<Windows.Media.MediaProperties.VideoEncodingProperties>()
        .Where(p => p != null 
            && !String.IsNullOrEmpty(p.Subtype) 
            && supportedVideoFormats.Contains(p.Subtype.ToLower()))
        .ToList();
var previewFormat = availableMediaStreamProperties.FirstOrDefault();

// Start Preview stream
await mediaCaptureManager.VideoDeviceController.SetMediaStreamPropertiesAsync(
    Windows.Media.Capture.MediaStreamType.VideoPreview, previewFormat);
await mediaCaptureManager.StartPreviewToCustomSinkAsync(
    new Windows.Media.MediaProperties.MediaEncodingProfile { Video = previewFormat }, previewSink);


// Set the source of the VideoBrush used for your preview
Microsoft.Devices.CameraVideoBrushExtensions.SetSource(viewfinderBrush, previewSink);
}

将这段代码添加到以前的代码中，它将起作用。重要的一点是在更改任何参数之前开始预览

在Windows Phone Silverlight 8.1上使用MediaCapture打开手电筒

1 个答案: