easyui 异步加载子节点（节点有复选框），节点选中而子节点未加载且未被选中

$("#Tree").tree({
	      checkbox: true, 
	      url: "XXX/XXXX/XXXXX", //加载全部节点
	      onBeforeExpand:function(node){ 
	    	
	          $("#Tree").tree("options").url = "XXX/XXXX/XXXXX?node=" + node.id;//加载父节点下的子节点
	      },
	      onCheck : function(node, checked) {
	    	  $("#Tree").tree('expand',node.target);
	      }
	 });

var width = $(window).width()-80;
var height = $(window).height()-120;
stView_layout = $('#stView_layout').layout({
width: width,
height: height
});
station_view = $('#stationView').window({
title: '测站导航',
left:50,
top:80,
width: width,
modal: false,
shadow: false,
closed: true,
height: height,
onResize:function(w,h){
if(stView_treegrid){
stView_treegrid.treegrid({
width:w-20,
height:h-260
});
}
}
});