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    partial class pictureBox1 : PictureBox
    {
        protected override void OnPaint(PaintEventArgs e)
        {
            //-----------------------------------------------------------------------
            // Es ist wichtig, dass wir (zuerst) die Oberklasse machen lassen.
            //-----------------------------------------------------------------------
            base.OnPaint(e);

            // Create pen.
            Pen blackPen = new Pen(Color.Black, 50);

            // Create rectangle.
            Rectangle rect = new Rectangle(0, 0, 300, 300);

            // Draw rectangle to screen.
            e.Graphics.DrawRectangle(blackPen, rect);

        }
    }