public void InitOverlay()
        {
            /**
             * 创建自定义overlay
             */
            mOverlay = new MyOverlay(this, Resources.GetDrawable(Resource.Drawable.icon_marka), mMapView);
            /**
             * 准备overlay 数据
             */
            GeoPoint p1 = new GeoPoint((int)(mLat1 * 1E6), (int)(mLon1 * 1E6));
            OverlayItem item1 = new OverlayItem(p1, "覆盖物1", "");
            /**
             * 设置overlay图标,如不设置,则使用创建ItemizedOverlay时的默认图标.
             */
            item1.Marker = Resources.GetDrawable(Resource.Drawable.icon_marka);

            GeoPoint p2 = new GeoPoint((int)(mLat2 * 1E6), (int)(mLon2 * 1E6));
            OverlayItem item2 = new OverlayItem(p2, "覆盖物2", "");
            item2.Marker = Resources.GetDrawable(Resource.Drawable.icon_markb);

            GeoPoint p3 = new GeoPoint((int)(mLat3 * 1E6), (int)(mLon3 * 1E6));
            OverlayItem item3 = new OverlayItem(p3, "覆盖物3", "");
            item3.Marker = Resources.GetDrawable(Resource.Drawable.icon_markc);

            GeoPoint p4 = new GeoPoint((int)(mLat4 * 1E6), (int)(mLon4 * 1E6));
            OverlayItem item4 = new OverlayItem(p4, "覆盖物4", "");
            item4.Marker = Resources.GetDrawable(Resource.Drawable.icon_gcoding);
            /**
             * 将item 添加到overlay中
             * 注意: 同一个itme只能add一次
             */
            mOverlay.AddItem(item1);
            mOverlay.AddItem(item2);
            mOverlay.AddItem(item3);
            mOverlay.AddItem(item4);
            /**
             * 保存所有item,以便overlay在reset后重新添加
             */
            mItems = new List<OverlayItem>();
            mItems.AddRange(mOverlay.AllItem);

            // 初始化 ground 图层
            mGroundOverlay = new GroundOverlay(mMapView);
            GeoPoint leftBottom = new GeoPoint((int)(mLat5 * 1E6),
                    (int)(mLon5 * 1E6));
            GeoPoint rightTop = new GeoPoint((int)(mLat6 * 1E6),
                    (int)(mLon6 * 1E6));
            Drawable d = Resources.GetDrawable(Resource.Drawable.ground_overlay);
            Bitmap bitmap = ((BitmapDrawable)d).Bitmap;
            mGround = new Ground(bitmap, leftBottom, rightTop);

            /**
             * 将overlay 添加至MapView中
             */
            mMapView.Overlays.Add(mOverlay);
            mMapView.Overlays.Add(mGroundOverlay);
            mGroundOverlay.AddGround(mGround);
            /**
             * 刷新地图
             */
            mMapView.Refresh();
            mResetBtn.Enabled = false;
            mClearBtn.Enabled = true;
            /**
             * 向地图添加自定义View.
             */
            viewCache = LayoutInflater.Inflate(Resource.Layout.custom_text_view, null);
            popupInfo = viewCache.FindViewById<View>(Resource.Id.popinfo);
            popupLeft = viewCache.FindViewById<View>(Resource.Id.popleft);
            popupRight = viewCache.FindViewById<View>(Resource.Id.popright);
            popupText = viewCache.FindViewById<TextView>(Resource.Id.textcache);

            button = new Button(this);
            button.SetBackgroundResource(Resource.Drawable.popup);

            /**
             * 创建一个popupoverlay
             */
            IPopupClickListener popListener = new IPopupClickListenerImpl(this);
            pop = new PopupOverlay(mMapView, popListener);
        }
        /**
     * 创建弹出泡泡图层
     */
        public void CreatePaopao()
        {

            ////泡泡点击响应回调
            IPopupClickListener popListener = new IPopupClickListenerImpl();
            pop = new PopupOverlay(mMapView, popListener);
        }