UWP MediaCapture FocusAsync: op无效

Question

我用MediapCapture扫描QrCode。这是我的配置：

var cameras = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture);
int cameraIndex = cameras.Count > 1 ? 1 : 0;
MediaCaptureInitializationSettings settings = new MediaCaptureInitializationSettings { VideoDeviceId = cameras[cameraIndex].Id };
settings.StreamingCaptureMode = StreamingCaptureMode.Video;

await _mediaCapture.InitializeAsync();
SetResolution();
_mediaCapture.SetPreviewRotation(VideoRotation.Clockwise90Degrees);
_mediaCapture.VideoDeviceController.FocusControl.Configure(new Windows.Media.Devices.FocusSettings() { Mode = Windows.Media.Devices.FocusMode.Auto });
videoCapture.Source = _mediaCapture;
await _mediaCapture.StartPreviewAsync();

我的CaptureElement上还有一个被点击的事件，它调用FocusAsync方法：

await _mediaCapture.VideoDeviceController.FocusControl.FocusAsync();

我的问题是，当我试图集中注意力时，有时(并不总是)有一个错误(即使这是我第一次调用它)。此错误是：

op是无效的

编辑：

下面是我的堆栈跟踪：(没有内部异常)

在System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task任务)在System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task任务)在System.Runtime.CompilerServices.TaskAwaiter.GetResult() at ProjectName.Views.QrCodeScannerPage.d__8.MoveNext()

Answer 1

最后，我从以下示例中选择设置自动焦点：https://msdn.microsoft.com/en-us/windows/uwp/audio-video-camera/capture-device-controls-for-photo-and-video-capture