openLayers地图缩放的回调

    //设置地图最小缩放级别为17级  
     map.events.register("zoomend", this, function (e) {  
        //每次地图缩放时就会进入到这
        if (map.getZoom() < 17)  
            {  
                //map.zoomTo(17);  
                map.setCenter(map.getCenter(),17);  
            }  
        });