System.Drawing参数无效

Question

I'm currently using AForge dll to render the video on the picture box for the live view. I do have a video frame function to whether WriteFrame or Screenshot the current picturebox frame as a JPG.

But i met a problem when sometime the program will prompt out an error of Parameter is not valid or Object is been used elsewhere. I did try to find solution to solve it and i pretty sure i did dispose on the image and the clone image, but the problem still exist.

Could you assist me on what i had done wrong with my program?

void videoSource_NewFrame(object sender, NewFrameEventArgs eventArgs)
        {
            //your code using bmp object
            if (D1Pic.BackColor == Color.Green)
            {
                video = (Bitmap)eventArgs.Frame.Clone();
                if (livePreview.Image != null)
                {
                    //Dispose the resources
                    this.Invoke(new MethodInvoker(delegate() { livePreview.Image.Dispose(); }));
                }
                livePreview.Image = (Bitmap)eventArgs.Frame.Clone();
                imgclone = (Image)livePreview.Image.Clone();
                FileWriter.WriteVideoFrame(video);
            }
            else
            {
                video = (Bitmap)eventArgs.Frame.Clone();
                if (livePreview.Image != null)
                {
                    //Dispose the resources
                    this.Invoke(new MethodInvoker(delegate() { livePreview.Image.Dispose(); }));
                    this.Invoke(new MethodInvoker(delegate() { video.Dispose(); }));
                }
                livePreview.Image = (Bitmap)eventArgs.Frame.Clone();
                imgclone = (Image)livePreview.Image.Clone();
            }
            video.Dispose();
            livePreview.Refresh();

Here are the stack trace error :

{"Parameter is not valid."}
   at System.Drawing.Image.get_Width()
   at System.Windows.Forms.PictureBox.ImageRectangleFromSizeMode(PictureBoxSizeMode mode)
   at System.Windows.Forms.PictureBox.OnPaint(PaintEventArgs pe)
   at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
   at System.Windows.Forms.Control.WmPaint(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

UPDATED CODE :

 var newFrame = (Bitmap)eventArgs.Frame.Clone();
                this.Invoke(new MethodInvoker(delegate()
                {
                    if (livePreview.Image != null)
                    {
                        livePreview.Image.Dispose();
                    }
                    livePreview.Image = newFrame;
                }));
                imgclone = (Bitmap)eventArgs.Frame.Clone();

                //Write frame into video
                if (D1Pic.BackColor == Color.Green)
                {
                    video = (Bitmap)eventArgs.Frame.Clone();
                    FileWriter.WriteVideoFrame(video);
                }

Answer 1

You are calling livePreview.Image.Dispose() in the UI thread, but you're not setting livePreview.Image to null afterwards.

So between the time that you dispose livePreview.Image and the time that you assign a new image to it, livePreview.Image points to a disposed object.

So I think occasionally your picturebox tries to draw itself during this time, and fails when it attempts to access its (disposed) Image property.

The solution would be:

if (livePreview.Image != null)
{
    //Dispose the resources
    this.Invoke(new MethodInvoker(delegate() { 
        livePreview.Image.Dispose(); 
        livePreview.Image = null;
    }));
}

Or even better, assign the new image in the same step:

var newFrame = (Bitmap)eventArgs.Frame.Clone();
this.Invoke(new MethodInvoker(delegate() { 
    if (livePreview.Image != null)
    {
        livePreview.Image.Dispose(); 
    }
    livePreview.Image = newFrame;
}));

In general, you need to understand what's happening with your various Bitmap objects. Anything that keeps a reference to a Bitmap that has been disposed will be a problem.