Question

我正在制作一个手电筒应用程序，我需要在按下ON按钮时不断使用相机的LED，并在按下相同的按钮时将其关闭。我遵循了这篇文章Turning on the LED with the video camera using Reflection。 ON / OFF操作只能正常工作一次。守则如下：

 private VideoCamera _videoCamera;
 private VideoCameraVisualizer _videoCameraVisualizer;
 bool _isFlashOff = true;

 private void FlashButton_Click(object sender, RoutedEventArgs e)
    {
        try
        {
            if (_isFlashOff)
            {
                _isFlashOff = false;

                // Check to see if the camera is available on the device.
                if (PhotoCamera.IsCameraTypeSupported(CameraType.Primary))
                {
                   // Use standard camera on back of device.
                    _videoCamera = new VideoCamera();
                   // Event is fired when the video camera object has been initialized.
                    _videoCamera.Initialized += VideoCamera_Initialized;

                    // Add the photo camera to the video source
                    _videoCameraVisualizer = new VideoCameraVisualizer();
                    _videoCameraVisualizer.SetSource(_videoCamera);
                }
            }
            else
            {                    
                _isFlashOff = true;
                _videoCamera.StopRecording();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    private void VideoCamera_Initialized(object sender, EventArgs e)
    {
        _videoCamera.LampEnabled = true;
        _videoCamera.StartRecording();
    }

由于在文章中指定的VideoCamera类中没有实现 StopRecording 方法：Turning on the LED with the video camera using Reflection。我的功能如下：

 public void StopRecording()
    {
        // Invoke the stop recording method on the video camera object.
         _videoCameraStopRecordingMethod.Invoke(_videoCamera, null);
    }

问题是当我再次按下ON按钮时“异常”被抛出为“TargetInvocationException”。我无法找出导致异常的问题。是否StopRecording（）函数正确.. ??

Answer 1

那是因为你应该只初始化一次相机。在OnNavigatedTo事件期间执行此操作，然后重复使用相同的实例：

    protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {                    
        // Use standard camera on back of device.
        _videoCamera = new VideoCamera();

        // Event is fired when the video camera object has been initialized.
        _videoCamera.Initialized += VideoCamera_Initialized;


        // Add the photo camera to the video source
        _videoCameraVisualizer = new VideoCameraVisualizer();
        _videoCameraVisualizer.SetSource(_videoCamera);
    }

    private void VideoCamera_Initialized(object sender, EventArgs e)
    {
        isInitialized = true;
    }

    bool isInitialized;
    bool isFlashEnabled;

    private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
    {
        if (!isInitialized)
        {
            MessageBox.Show("Please wait during camera initialization");
            return;
        }

        if (!isFlashEnabled)
        {
            isFlashEnabled = true;

            // Check to see if the camera is available on the device.
            if (PhotoCamera.IsCameraTypeSupported(CameraType.Primary))
            {
                _videoCamera.LampEnabled = true;
                _videoCamera.StartRecording();
            }
        }
        else
        {
            isFlashEnabled = false;

            _videoCamera.StopRecording();
        }
    }

Answer 2

试试这个：

http://msdn.microsoft.com/en-us/library/hh202949.aspx

如何使用Windows Phone 7中的Reflection停止led手电筒/手电筒应用程序

2 个答案: