一起学习ArcEngine（3）缩小

继承自定义基类ToolBase，代码如下，比以前清爽多了！

    /// <summary>
    /// 地图缩小工具
    /// </summary>
    public class ZoomOut : ToolBase
    {
        private INewEnvelopeFeedback m_feedBack;
        private IPoint m_point;
        private Boolean m_isMouseDown;

         #region 实例化
        public ZoomOut()
            :base("ZoomOut")
        {
            if (m_cursor == null) m_cursor = getCursor(esriSystemMouseCursor.esriSystemMouseCursorZoomOut);
        }

        public ZoomOut(AxMapControl mapCtl)
            : base(mapCtl, "ZoomOut")
        {
            if (m_cursor == null) m_cursor = getCursor(esriSystemMouseCursor.esriSystemMouseCursorZoomOut);
        }

        public ZoomOut(AxPageLayoutControl plCtl)
            : base(plCtl, "ZoomOut")
        {
            if (m_cursor == null) m_cursor = getCursor(esriSystemMouseCursor.esriSystemMouseCursorZoomOut);
        }
        #endregion

        protected override void initContextMenu()
        {
            ContextMenu cmenu = new ContextMenu();
            MenuItem m = new MenuItem();
            m.Text = "结束";
            m.Click += new EventHandler(m_Click);
            cmenu.MenuItems.Add(m);
            m_contextMenu = cmenu;

        }

        void m_Click(object sender, EventArgs e)
        {
            if (m_pControl is AxMapControl)
            {
                AxMapControl am = m_pControl as AxMapControl;
                am.CurrentTool = null;
            }
        }


        public override void OnMouseDown(int Button, int Shift, int X, int Y)
        {
            if (m_pActiveView == null) return;
            if (Button == 2)
            {
                ShowContextMenu(X, Y);
                return;
            }

            m_point = m_pActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(X, Y);
            m_cursor = getCursor(ESRI.ArcGIS.SystemUI.esriSystemMouseCursor.esriSystemMouseCursorZoomOut);
            m_isMouseDown = true;

        }

        public override void OnMouseMove(int Button, int Shift, int X, int Y)
        {
            if (!m_isMouseDown) return;

            //Start an envelope feedback
            if (m_feedBack == null)
            {
                m_feedBack = new NewEnvelopeFeedbackClass();
                m_feedBack.Display = m_pActiveView.ScreenDisplay;
                m_feedBack.Start(m_point);
            }
            //Move the envelope feedback
            m_feedBack.MoveTo(m_pActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(X, Y));
        }

        public override void OnMouseUp(int Button, int Shift, int X, int Y)
        {
            if (!m_isMouseDown) return;

            IEnvelope pEnvelope;
            IEnvelope pFeedEnvelope;

            double newWidth, newHeight;

            //If an envelope has not been tracked
            if (m_feedBack == null)
            {
                //Zoom out from the mouse click
                pEnvelope = m_pActiveView.Extent;
                pEnvelope.Expand(2, 2, true);
                pEnvelope.CenterAt(m_point);
            }
            else
            {
                //Stop the envelope feedback
                pFeedEnvelope = m_feedBack.Stop();

                //Exit if the envelope height or width is 0
                if (pFeedEnvelope.Width == 0 || pFeedEnvelope.Height == 0)
                {
                    m_feedBack = null;
                    m_isMouseDown = false;
                }

                newWidth = m_pActiveView.Extent.Width * (m_pActiveView.Extent.Width / pFeedEnvelope.Width);
                newHeight = m_pActiveView.Extent.Height * (m_pActiveView.Extent.Height / pFeedEnvelope.Height);

                //Set the new extent coordinates
                pEnvelope = new EnvelopeClass();
                pEnvelope.PutCoords(m_pActiveView.Extent.XMin - ((pFeedEnvelope.XMin - m_pActiveView.Extent.XMin) * (m_pActiveView.Extent.Width / pFeedEnvelope.Width)),
                    m_pActiveView.Extent.YMin - ((pFeedEnvelope.YMin - m_pActiveView.Extent.YMin) * (m_pActiveView.Extent.Height / pFeedEnvelope.Height)),
                    (m_pActiveView.Extent.XMin - ((pFeedEnvelope.XMin - m_pActiveView.Extent.XMin) * (m_pActiveView.Extent.Width / pFeedEnvelope.Width))) + newWidth,
                    (m_pActiveView.Extent.YMin - ((pFeedEnvelope.YMin - m_pActiveView.Extent.YMin) * (m_pActiveView.Extent.Height / pFeedEnvelope.Height))) + newHeight);
            }

            //Set the new extent
            m_pActiveView.Extent = pEnvelope;

            //Refresh the active view
            m_pActiveView.Refresh();
            m_feedBack = null;
            m_isMouseDown = false;
        }

        public void OnKeyDown(int keyCode, int shift)
        {
            if (m_isMouseDown)
            {
                if (keyCode == 27) //ESC key
                {
                    m_feedBack = null;
                    m_isMouseDown = false;
                    m_pHookHelper.ActiveView.PartialRefresh(esriViewDrawPhase.esriViewForeground, null, null);
                }
            }
        }
    }