c# - 如何在C#中停止相机？使用grabber.dispose时出错

Question

我正在用C#开发一个项目。我有一个停止按钮，它调用grabber.dispose，但是当我单击它时，应用程序崩溃并且出现以下错误:

object reference is not set to an instance of object.

FrameGrabber函数应停止程序并将其移至当前帧。

捕获采集卡:

     private void FDButton_Click(object sender, EventArgs e)
            {
                CameraCapture();
                Application.Idle += new EventHandler(FrameGrabber);
                //initalize Frame grabber event
                FDButton.Enabled = false;
            }

            private void FrameGrabber(object sender, EventArgs e)
            {


                    currentFrame = grabber.QueryFrame().Resize(320, 240, Emgu.CV.CvEnum.INTER.CV_INTER_CUBIC);
                    //convert frame to gray scale
                    gray = currentFrame.Convert<Gray, Byte>();
                    //now detect face by using classifier
                    MCvAvgComp[][] facesDetected = gray.DetectHaarCascade(

                        face,//name of cascade
                        1.2,
                        10,
                        Emgu.CV.CvEnum.HAAR_DETECTION_TYPE.DO_CANNY_PRUNING,
                        new Size(20, 20));

                    //now check each frame of imagebox containing video and detect face
                    foreach (MCvAvgComp f in facesDetected[0])
                    {
                        //if face found increment t
                        t = t + 1;
                        //now see result by copying detected face in a frame name as result
                        result = currentFrame.Copy(f.rect).Convert<Gray, byte>().Resize(100, 100, Emgu.CV.CvEnum.INTER.CV_INTER_CUBIC);
                        //we convert current frame to gray scale and resize to 200x100
                        //now draw rectangle on detected image
                        currentFrame.Draw(f.rect, new Bgr(Color.Red), 2);
                    }



                    //view currentframe in imported imagebox
                    DetectionImageBox.Image = currentFrame;



            }

相机拍摄功能:

 public void CameraCapture()
        {
            grabber = new Capture();
            grabber.QueryFrame();
        }

取消按钮:

        private void FDStopButton_Click(object sender, EventArgs e)
        {
            grabber.Dispose();

        } 

Answer 1

这很可能是由于您已订阅Idle事件处理程序而发生的。

Application.Idle += new EventHandler(FrameGrabber);

FrameGrabber仍被订阅，但是通过调用dispose，您已将FrameGrabber设置为空引用，因此当事件触发时，您将获得异常。

您需要取消订阅事件处理程序，因此不会发生这种情况:

   private void FDStopButton_Click(object sender, EventArgs e)
   {
       Application.Idle -= FrameGrabber;
       grabber.Dispose();
   } 

您可以在此处查看有关退订的更好说明:
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/events/how-to-subscribe-to-and-unsubscribe-from-events