如何使用PictureBox打开/关闭相机

Question

IDE : Visual Studio 2010 Express
Lib : Emgu CV 2.2 Level : Beginner

I've make Camera ON when Clicking PictureBox and viceversa, but it giving error :

Object reference not set to an instance of an object

Here the Event Handler :

private void pictureBoxCapture_Click(object sender, EventArgs e)
{
    try
    {
        if (Clicked == true) //i dont know how to make it right
        {
            Application.Idle -= ProcessFrame;
        }
        else
        {
            Application.Idle += ProcessFrame;
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

Calling from :

private void ProcessFrame(object sender, EventArgs e)
{
    //Cap = new Emgu.CV.Capture();
    ImageFrame = Cap.QueryFrame();
    pictureBoxCapture.Image = ImageFrame.ToBitmap();
}

how to set if else parameter likely, any advice?

Answer 1

Create a class level Boolean variable, then toggle it in your PictureBox's click event.

public partial class Form1 : Form
{
    bool Clicked; //Create this Class level variable to be used in your handler
    public Form1()
    {
        InitializeComponent();
    }

    private void pictureBoxCapture_Click(object sender, EventArgs e)
    {
        Clicked =! Clicked; //Toggle your Boolean here
        try
        {
            if (Clicked)
            {
                Application.Idle -= ProcessFrame;
                FaceDetect();
            }
            else
            {
                Application.Idle += ProcessFrame;
            }
        }
        catch (Exception ex)
        {

            MessageBox.Show(ex.Message);
        }
    }
}

Answer 2

I expect your error is not being thrown by the picturebox click event but the ProcessFrame() event. It will have the habit of firing once after you have removed the Application.Idle -= ProcessFrame; however there will be no image in the event argument to work with. Instead use this code as your ProcessFrame() event:

private void ProcessFrame(object sender, EventArgs e)
{
    //Cap = new Emgu.CV.Capture();
    ImageFrame = Cap.QueryFrame();
    //Look for image content if null do nothing
    if(ImageFrame != null)
    {
        pictureBoxCapture.Image = ImageFrame.ToBitmap();
        //do any other operations on the image
    }
}

Cheers,

Chris