InvalidOperationException - object is currently in use elsewhere - red cross

Question

Hello

I have a C# desktop application in which one thread that I create continously gets an image from a

source(it's a digital camera actually) and puts it on a panel(panel.Image = img) in the GUI(which

must be another thread as it is the code-behind of a control.

The application works but on some machines I get the following error at random time

intervals(unpredictable)

************** Exception Text **************System.InvalidOperationException: The object is currently in use elsewhere.

Then the panel turns into a red cross, red X - i think this is the invalid picture icon that is

editable from the properties. The application keeps working but the panel is never updated

From what I can tell this error comes from the control's onpaint event where I draw something else

on the picture

I tried using a lock there but no luck :(

The way I call the function that puts the image on the panel is as follows:

if (this.ReceivedFrame != null)
   {
                Delegate[] clients = this.ReceivedFrame.GetInvocationList();
                foreach (Delegate del in clients)
                {
                    try
                    {
                        del.DynamicInvoke(new object[] { this, new StreamEventArgs(frame) });
                    }
                    catch { }
                }
            }

this is the delegate:

public delegate void ReceivedFrameEventHandler(object sender, StreamEventArgs e); public event ReceivedFrameEventHandler ReceivedFrame;

and this is how the function inside the control code-behind registers to it:

Camera.ReceivedFrame += new Camera.ReceivedFrameEventHandler(camera_ReceivedFrame);

I also tried

del.Method.Invoke(del.Target, new object[] { this, new StreamEventArgs(b) });

instead of

del.DynamicInvoke(new object[] { this, new StreamEventArgs(frame) });

but no luck

Does anyone know how I could fix this error or at least catch the error somehow and make the thread put the images on the panel once again?

Can anyone help please? I am really stuck Thank you in advance

Answer 1

I think this is multithreading problem Use windows golden rule and update the panel in the main thread use panel.Invoke This should overcome cross threading exception

Answer 2

This is because Gdi+ Image class is not thread safe. Hovewer you can avoid InvalidOperationException by using lock every time when you need to Image access, for example for painting or getting image size:

Image DummyImage;

// Paint
lock (DummyImage)
    e.Graphics.DrawImage(DummyImage, 10, 10);

// Access Image properties
Size ImageSize;
lock (DummyImage)
    ImageSize = DummyImage.Size;

BTW, invocation is not needed, if you will use the above pattern.

Answer 3

I tryed locking e in my procedure I cannot lock the image because I am not working with it I am drawing lines on top of it

lock (e)
        {


            //draw left | upper half
            e.Graphics.DrawLine(dp, iCropLeft, iCropRight + iLittleSquareSide / 2, iCropLeft, iCropRight + iCropHeight / 2 - iLittleSquareSide / 2);

            //there was a lot more code here just like this but I deleted it 
            //in order to keep it concise

            //draw crosshair -

            e.Graphics.DrawLine(dp, 0, pbPreviewCamera.Size.Height / 2, pbPreviewCamera.Size.Width, pbPreviewCamera.Size.Height / 2);
        }

I still get the error:

************** Exception Text **************

System.InvalidOperationException: Object is currently in use elsewhere. at System.Drawing.Image.get_Height() 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, Boolean disposeEventArgs) 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.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Should I lock something else?