Question

我正在尝试通过Windows Phone应用程序中的TorchControl类操作手电筒应用程序：这是我的代码

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));
    }


    async private void Button_Click(object sender, RoutedEventArgs e)
   {
       var cameraID = await GetCameraID(Windows.Devices.Enumeration.Panel.Back);
       var mediaDev = new MediaCapture();
       await mediaDev.InitializeAsync(new MediaCaptureInitializationSettings
       {
           StreamingCaptureMode = StreamingCaptureMode.Video,
           PhotoCaptureSource = PhotoCaptureSource.VideoPreview,
           AudioDeviceId = String.Empty,
           VideoDeviceId = cameraID.Id
       });
       var videoDev = mediaDev.VideoDeviceController;
       var tc = videoDev.TorchControl;
       if (tc.Supported)         
           tc.Enabled = true;
       mediaDev.Dispose();          
   }

但问题是，每当我第二次点击按钮时应用程序崩溃。我被告知使用mediaDev.Dispose（）方法，但它也无法正常工作。这是例外：

发生了'System.Exception'类型的第一次机会异常 mscorlib.ni.dll WinRT信息：与此错误关联的文本无法找到代码。

当“initializeasync”中的文字突出显示时显示

Answer 1

MediaCapture在重新初始化时会抛出异常。要解决此问题，请在导航回“相机”页面或单击相机按钮时确保不要初始化MediaCapture 。

    MediaCapture mediacapture = new MediaCapture();
    bool initialized;
    protected async override void OnNavigatedTo(NavigationEventArgs e)
    {
        if (initialized == false)
        {
            var cameraID = await GetCameraID(Windows.Devices.Enumeration.Panel.Back);
            await mediacapture.InitializeAsync(new MediaCaptureInitializationSettings
            {
                StreamingCaptureMode = StreamingCaptureMode.Video,
                PhotoCaptureSource = PhotoCaptureSource.Photo,
                AudioDeviceId = string.Empty,
                VideoDeviceId = cameraID.Id
            });
        }
        //Selecting Maximum resolution for Video Preview
        var maxPreviewResolution = mediacapture.VideoDeviceController.GetAvailableMediaStreamProperties(MediaStreamType.VideoPreview).Aggregate((i1, i2) => (i1 as VideoEncodingProperties).Height > (i2 as VideoEncodingProperties).Height ? i1 : i2);
        //Selecting 4rd resolution setting
        var selectedPhotoResolution = mediacapture.VideoDeviceController.GetAvailableMediaStreamProperties(MediaStreamType.Photo).ElementAt(3);
        await mediacapture.VideoDeviceController.SetMediaStreamPropertiesAsync(MediaStreamType.Photo, selectedPhotoResolution);
        await mediacapture.VideoDeviceController.SetMediaStreamPropertiesAsync(MediaStreamType.VideoPreview, maxPreviewResolution);
        // in my .xaml <CaptureElement Name="viewfinder" />
        viewfinder.Source = mediacapture;
        mediacapture.SetPreviewRotation(VideoRotation.Clockwise90Degrees);
        await mediacapture.StartPreviewAsync(); 
        initialized = true;
    }

此外，在导航到其他页面之前或在相机再次开始预览之前，请确保相机停止预览。没有必要处置MediaCapture。

    private async void GoBack_Click(object sender, RoutedEventArgs e)
    {     
        await mediacapture.StopPreviewAsync();
        this.Frame.Navigate(typeof(MainPage));
        //Not needed
        //mediacapture.Dispose();
    }

GetCameraID 方法归功于Romasz的博客。 http://www.romasz.net/how-to-take-a-photo-in-windows-runtime/

Answer 2

此问题可能与多线程有关：使用默认值（即不更改SynchronizationContext）对await的调用将继续另一个线程上的方法，图形和媒体库并不总是支持这种方法（我有SFML，WPF和AutoCAD的第一手经验让人非常高兴，仅举几例）。虽然存在InitializeAsync方法，但请确保在主线程上不需要进行处理。

每次在Windows Phone中Flashlight应用程序崩溃

2 个答案: