System.InvalidOperationException: Object is currently in use elsewhere

Question

I seem to be getting this error when trying to draw on a panel. Im no expert in C# so hopefully someone here can help me with this. Thanks in advance.

The stack trace shows,

at System.Drawing.Graphics.set_Transform(Matrix value) at Victoria.Robotics.Marvin.Teleoperation.MainForm.DrawXYAxis(Graphics g) in C:\Users\kasunt\Microsoft Robotics Dev Studio 2008 R3\Marvin\Teleoperation\MainForm.cs:line 2173 at Victoria.Robotics.Marvin.Teleoperation.MainForm.envMap_Paint(Object sender, PaintEventArgs e) in C:\Users\kasunt\Microsoft Robotics Dev Studio 2008 R3\Marvin\Teleoperation\MainForm.cs:line 2143 at System.Windows.Forms.Control.OnPaint(PaintEventArgs e) 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.ScrollableControl.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)

The code is below. Error seems to occur when setting the transform,

    private void envMap_Paint(object sender, PaintEventArgs e)
    {
        DrawXYAxis(e.Graphics);
    }

    /// <summary>
    /// Helper to draw the XY axis and plot the map
    /// </summary>
    public void DrawXYAxis(Graphics g)
    {
        Rectangle rect = envMap.ClientRectangle;

        myPen = new Pen(Color.Black, 1);
        g.PageUnit = GraphicsUnit.Millimeter;
        g.PageScale = 0.1F;
        IntPtr hdc = g.GetHdc();
        int hMemDC = hdc.ToInt32();

        // Reverse the axis of the drawing surface
        Matrix mx = new Matrix(1, 0, 0, -1, 0, envMap.ClientSize.Height * 2);
        g.Transform = mx;
        g.TranslateTransform(50, 100, MatrixOrder.Append);

        // For drawing X - AXIS
        g.DrawLine(myPen, 0, 0, (2 * rect.Right - 60), 0);
        // For drawing Y - AXIS
        g.DrawLine(myPen, 0, 0, 0, 2 * rect.Bottom);

        // For drawing Arrow on X-AXIS
        g.DrawLine(myPen, (2 * rect.Right - 60) - 15, 8, (2 * rect.Right - 60), 0);
        g.DrawLine(myPen, (2 * rect.Right - 60), 0, (2 * rect.Right - 60) - 15, -8);

        // For drawing Arrow on Y-AXIS
        g.DrawLine(myPen, 8, 2 * rect.Bottom - 15, 0, 2 * rect.Bottom);
        g.DrawLine(myPen, 0, 2 * rect.Bottom, -8, 2 * rect.Bottom - 15);

        // Save the state to restore later
        GraphicsState state = g.Save();

        // Create a matrix to offset the text to the desired position and flip it the
        // right way up again
        Matrix mx2 = new Matrix(1, 0, 0, -1, 0, 0);
        Matrix mx1 = mx.Clone();
        mx1.Multiply(mx2);
        g.Transform = mx1;
        SolidBrush drawBrush = new SolidBrush(Color.Black);
        Font drawFont = new Font("Microsoft Sans Serif", 9, FontStyle.Bold);
        StringFormat sF = new StringFormat(StringFormatFlags.NoClip);
        sF.Alignment = StringAlignment.Center;
        g.DrawString("X", drawFont, drawBrush, (2 * rect.Right - 40), -2 * Font.Height, sF);
        g.DrawString("Y", drawFont, drawBrush, -40, -(2 * rect.Height + 2 * Font.Height), sF);

        // Restore state
        g.Restore(state);

        drawFont = new Font("Microsoft Sans Serif", 7);

        // Drawing Tick Marks and Labels
        // NOTE THE LABELS ON THE AXES WILL CHANGE TO REFFECT THE REAL POSITION OF THE ROBOT....
        myPen.Dispose();
   }

Line #2173,

        g.Transform = mx;

Line #2143,

        DrawXYAxis(e.Graphics);

Hans Passant Hans Passant · Accepted Answer · 2012-04-03T15:04:42

This is an exception that's normally caused by illegally using a Graphics context in another thread. I would have to guess there's other code in your program that is also doing something with graphics.

If you have no idea what that code might be then use Debug + Windows + Threads and look through the call stacks of the threads listed there. Also look for any assignment to Control.CheckForIllegalCrossThreadCalls in your source code. You'll want to delete that statement so you get better diagnostics when you violate threading requirements.

System.InvalidOperationException: Object is currently in use elsewhere

2 Answers