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[英]Writing a Simple Video Viewer/Frame Grabber in C# for a USB Camera
[英]How to stop a camera in c#? Error while using grabber.dispose
我正在用C#開發一個項目。 我有一個停止按鈕,它調用grabber.dispose,但是當我單擊它時,應用程序崩潰了,並出現以下錯誤:
對象引用未設置為對象的實例。
FrameGrabber函數應停止程序並將其移至當前幀。
捕獲采集卡:
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;
}
相機拍攝功能:
public void CameraCapture()
{
grabber = new Capture();
grabber.QueryFrame();
}
取消按鈕:
private void FDStopButton_Click(object sender, EventArgs e)
{
grabber.Dispose();
}
這很可能是由於您已訂閱Idle事件處理程序而發生的。
Application.Idle += new EventHandler(FrameGrabber);
FrameGrabber仍被訂閱,但是通過調用dispose,您已將FrameGrabber設置為空引用,因此,在事件觸發時,您將獲得異常。
您需要取消訂閱事件處理程序,因此不會發生這種情況:
private void FDStopButton_Click(object sender, EventArgs e)
{
Application.Idle -= FrameGrabber;
grabber.Dispose();
}
您可以在此處查看有關取消訂閱的更好描述: https : //docs.microsoft.com/zh-cn/dotnet/csharp/programming-guide/events/how-to-subscribe-to-and-and-unsubscribe-from-events
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