放大 缩小

 case "放大":
                    MyDrawObject.IsEnabled = true;
                    _toolmode = "zoomin";
                    break;
                case "缩小":
                    MyDrawObject.IsEnabled = true;
                    _toolmode = "zoomout";
                    break;

 void MyDrawObject_DrawComplete(object sender,DrawEventArgs E)
        {
            if (_toolmode == "zoomin")
            {
                Mymap.ZoomTo(e.Geometry as ESRI.ArcGIs.CLIENt.Geometry.EnvelopE);
            }
            else if (_toolmode == "zoomout")
            {
                Envelope currentextent = Mymap.Extent;

                Envelope zoomBoxExtent = e.Geometry as Envelope;
                MapPoint zoomBoxCenter = zoomBoxExtent.GetCenter();

                double whRatioCurrent = currentextent.Width / currentextent.Height;
                double whRatioZoomBox = zoomBoxExtent.Width / zoomBoxExtent.Height;

                Envelope newEnv = null;

                if (whRatioZoomBox > whRatioCurrent)
                // use width
                {
                    double mapWidthPixels = Mymap.Width;
                    double multiplier = currentextent.Width / zoomBoxExtent.Width;
                    double newWidthMapUnits = currentextent.Width * multiplier;
                    newEnv = new Envelope(new MapPoint(zoomBoxCenter.X - (newWidthMapUnits / 2),zoomBoxCenter.Y),new MapPoint(zoomBoxCenter.X + (newWidthMapUnits / 2),zoomBoxCenter.Y));
                }
                else
                // use height
                {
                    double mapHeightPixels = Mymap.Height;
                    double multiplier = currentextent.Height / zoomBoxExtent.Height;
                    double newHeightMapUnits = currentextent.Height * multiplier;
                    newEnv = new Envelope(new MapPoint(zoomBoxCenter.X,zoomBoxCenter.Y - (newHeightMapUnits / 2)),new MapPoint(zoomBoxCenter.X,zoomBoxCenter.Y + (newHeightMapUnits / 2)));
                }

                if (newEnv != null)
                    Mymap.ZoomTo(newEnv);
            }
        }

  MyDrawObject = new Draw(Mymap)
            {
                FillSymbol = LayoutRoot.resources["DefaultFillSymbol"] as ESRI.ArcGIs.CLIENt.Symbols.FillSymbol,DrawMode = DrawMode.Rectangle
            };
            MyDrawObject.DrawComplete += new EventHandler<DrawEventArgs>(MyDrawObject_DrawCompletE);