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我已经实现了媒体流源类。当我点击一些时，我想停止相机馈送。关闭媒体元素和媒体流源的正确方法是什么。这样我的应用程序就不会崩溃。

这是我的简单代码Mainpage.xaml.cs，CamerastreamSource源自MediaStreamSource

MainPage.xaml.cs 文件代码。 

 async void MainPage_Loaded(object sender, RoutedEventArgs e) {
        Windows.Foundation.Size size;
        PhotoCaptureDevice m_camera;
        CameraStreamsource m_vf;
        Debug.WriteLine("supported capture resolution:");
        foreach (var i in PhotoCaptureDevice.GetAvailableCaptureResolutions
            (CameraSensorLocation.Back)) {
            Debug.WriteLine(i.Height + "," + i.Width);
        }
        size = PhotoCaptureDevice.GetAvailableCaptureResolutions
            (CameraSensorLocation.Back).First();



        m_camera = await PhotoCaptureDevice.OpenAsync(CameraSensorLocation.Back, size);



        // Resolve and set the preview resolution
        Debug.WriteLine("supported preview resolution:");

        size.Width = 640; size.Height = 480; 
        await m_camera.SetPreviewResolutionAsync(size);
        m_vf = new CameraStreamSource(m_camera,this);
         //_mediaElement is the MediaElemet control in MainPage.xaml 
        _mediaElement.SetSource(m_vf);
    }

CameraStreamSource : MediaStreamSource代码

class CameraStreamSource : MediaStreamSource {



     //private AudioVideoCaptureDevice _device;
    public PhotoCaptureDevice _device;
    private long _currentTime;
    private readonly Dictionary<MediaSampleAttributeKeys, string> _emptySampleDict =
        new Dictionary<MediaSampleAttributeKeys, string>();

    //viewfinder display
    private MediaStreamDescription _videoStreamDes;
    private byte[] _byteBuf =null;      
    private MemoryStream _stream;
    MediaStreamSample _sample = null;


    public CameraStreamSource(PhotoCaptureDevice device,MainPage obj)
    {
        mainPage = obj;
        _device = device;

    }

    protected override void GetSampleAsync(MediaStreamType mediaStreamType)
    {
        _device.GetPreviewBufferYCbCr(_byteBuf);
        if (_sample == null)
        {
            _sample = new MediaStreamSample(_videoStreamDes, _stream, 0, _stream.Length, _currentTime, _emptySampleDict);
        }

        ReportGetSampleCompleted(_sample);
    }
    protected override void OpenMediaAsync()
    { 
        // todo
        Dictionary<MediaSourceAttributesKeys, string> mediaSourceAttributes =
            new Dictionary<MediaSourceAttributesKeys, string>();
        Dictionary<MediaStreamAttributeKeys, string> mediaStreamAttributes =
            new Dictionary<MediaStreamAttributeKeys, string>();
        List<MediaStreamDescription> mediaStreamDescriptions =
            new List<MediaStreamDescription>();


        mediaStreamAttributes[MediaStreamAttributeKeys.VideoFourCC] = "YV12";
        mediaStreamAttributes[MediaStreamAttributeKeys.Width] = _device.PreviewResolution.Width.ToString();
        mediaStreamAttributes[MediaStreamAttributeKeys.Height] = _device.PreviewResolution.Height.ToString();

        _videoStreamDes =
            new MediaStreamDescription(MediaStreamType.Video, mediaStreamAttributes);
        mediaStreamDescriptions.Add(_videoStreamDes);

        // a zero timespan is an infinite video
        mediaSourceAttributes[MediaSourceAttributesKeys.Duration] =
            TimeSpan.FromSeconds(0).Ticks.ToString(CultureInfo.InvariantCulture);

        mediaSourceAttributes[MediaSourceAttributesKeys.CanSeek] = false.ToString();

        // Report that we finished initializing its internal state and can now
        // pass in frame samples.
        ReportOpenMediaCompleted(mediaSourceAttributes, mediaStreamDescriptions);

        _byteBuf = new byte[(int)((_device.PreviewResolution.Width * _device.PreviewResolution.Height) * 1.5)];

        _stream = new MemoryStream(_byteBuf);


    }

    protected override void SeekAsync(long seekToTime)
    {
        // todo
        _currentTime = seekToTime;
        ReportSeekCompleted(seekToTime);
    }


    protected override void CloseMedia() {

        // No implementation required

    }
    protected override void GetDiagnosticAsync(MediaStreamSourceDiagnosticKind diagnosticKind) {
        throw new NotImplementedException();
    }

    protected override void SwitchMediaStreamAsync(MediaStreamDescription mediaStreamDescription) {
        throw new NotImplementedException();
    }

任何预兆都可以帮助我，我如何在一些类似按钮上优雅地点击关闭它。我实际上需要代码来MediaElement优雅MediaStreamSource地关闭

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