private CircleWindow OpenNewCircleWindow(string fileName, string circleId, Circle circle)
        {
            CircleWindow cw = new CircleWindow(circleId, circle, fileName, true);

            circleWindows.Add(circleId, cw);

            cw.MdiParent = mainWindow;
            cw.Show();

            cw.Closing += (sender, closingEvent) => {
                if (OnCircleWindowClose(cw.Id))
                {
                    closingEvent.Cancel = true;
                }
            };

            return(cw);
        }
        private CircleWindow CreateNewCircleWindow()
        {
            string       circleId = string.Format("Circle_{0}", (circleWindows.Count + 1));
            CircleWindow cw       = new CircleWindow(circleId);

            circleWindows.Add(circleId, cw);

            cw.MdiParent = mainWindow;
            cw.Show();

            cw.Closing += (sender, closingEvent) => {
                if (OnCircleWindowClose(cw.Id))
                {
                    closingEvent.Cancel = true;
                }
            };

            return(cw);
        }