C#鹰眼_带拖动

结合help中给的例子，又使用DisPlayFeedBack，实现在鹰眼中拖动。拖动过程中小边框的显示问题解决的不是很好，还望大家多多指教。
实现如下：
两个MapControl控件：axMapControl1和axMapControl2，axMapControl2存放鹰眼地图。
主要变量有：
private IEnvelope m_Envelope;  //The envelope drawn on the small MapControl---axMapControl2.
private System.Object m_FillSymbol;  //The symbol used to draw the envelope on the small MapControl

//axMapControl1中的事件

private void CreateOverviewSymbol() //create the symbol used in the small MapControl ，自定义函数
        {
            //Get the IRGBColor interface.
            IRgbColor color = new RgbColorClass();
            //Set the color properties.
            color.RGB = 255;
            //Get the ILine symbol interface.
            ILineSymbol outline = new SimpleLineSymbolClass();
            //Set the line symbol properties.
            outline.Width = 1.5;
            outline.Color = color;
            //Get the IFillSymbol interface.
            ISimpleFillSymbol simpleFillSymbol = new SimpleFillSymbolClass();
            //Set the fill symbol properties.
            simpleFillSymbol.Outline = outline;
            simpleFillSymbol.Style = esriSimpleFillStyle.esriSFSHollow;
            m_FillSymbol = simpleFillSymbol;
        }
private void axMapControl1_OnMapReplaced(object sender, ESRI.ArcGIS.Controls.IMapControlEvents2_OnMapReplacedEvent e) //更新axMapControl1地图时装载鹰眼地图
        {
            axMapControl2.LoadMxFile(axMapControl1.DocumentFilename);
            axMapControl2.Extent=axMapControl1.FullExtent;                      
            m_Envelope = axMapControl1.ActiveView.Extent;
        }

private void axMapControl1_OnExtentUpdated(object sender, IMapControlEvents2_OnExtentUpdatedEvent e)
        {  //axMapControl1的范围变化时，设置鹰眼小边框m_Envelope 的大小
            axMapControl2.ActiveView.PartialRefresh(esriViewDrawPhase.esriViewForeground, null, null);
            m_Envelope = e.newEnvelope as IEnvelope;
        }
private void axMapControl1_OnAfterDraw(object sender, IMapControlEvents2_OnAfterDrawEvent e)
        {
            if (m_Envelope == null) return;
           //If the foreground phase has drawn.
            esriViewDrawPhase viewDrawPhase = (esriViewDrawPhase)e.viewDrawPhase;
            if (viewDrawPhase == esriViewDrawPhase.esriViewForeground)
            {
                axMapControl2.DrawShape(m_Envelope as IGeometry, ref m_FillSymbol);
            }
        }
几个变量：
private IMoveEnvelopeFeedback pSmallViewerEnvelope;//鹰眼小地图的红框
private IPoint pSmallViewerMouseDownPt;//拖动时鼠标落点
private bool isTrackingSmallViewer = false; //标识是否在拖动
static int moveCount = 0;//记录移动的个数，为移动过程中显示红框用。权宜之计，望高手提出更好解决方案

//axMapControl2中的事件
private void axMapControl2_OnMouseDown(object sender, IMapControlEvents2_OnMouseDownEvent e)//鹰眼互动
        {
            //IPoint pt = new PointClass();
            pSmallViewerMouseDownPt = new PointClass();
            pSmallViewerMouseDownPt.PutCoords(e.mapX, e.mapY);
            axMapControl1.CenterAt(pSmallViewerMouseDownPt);

            isTrackingSmallViewer = true;
            if (pSmallViewerEnvelope == null)
            {
                pSmallViewerEnvelope = new MoveEnvelopeFeedbackClass();
                pSmallViewerEnvelope.Display = axMapControl2.ActiveView.ScreenDisplay;
                pSmallViewerEnvelope.Symbol = (ISymbol)m_FillSymbol;
            }
            pSmallViewerEnvelope.Start(m_Envelope, pSmallViewerMouseDownPt);
           
        }
      
       private void axMapControl2_OnMouseMove(object sender, IMapControlEvents2_OnMouseMoveEvent e)
        {
            if (isTrackingSmallViewer)
            {
                moveCount++;
                if (moveCount % 4 == 0)//因为一刷新，红框就没了。所以每移动4次就刷新一下，保持红框的连续性。
                    axMapControl2.ActiveView.PartialRefresh(esriViewDrawPhase.esriViewForeground, null, null);
                pSmallViewerMouseDownPt.PutCoords(e.mapX, e.mapY);
                pSmallViewerEnvelope.MoveTo(pSmallViewerMouseDownPt);
            }           
        }
       private void axMapControl2_OnMouseUp(object sender, IMapControlEvents2_OnMouseUpEvent e)
        {
            if (pSmallViewerEnvelope != null)
            {
                m_Envelope = pSmallViewerEnvelope.Stop();
                axMapControl1.Extent = m_Envelope;
                isTrackingSmallViewer = false;              
            }
        }