treegrid複選框選中

碰到個EasyUI複選框選中問題，困擾好一會，記錄下

resTreeGrid = $('#resTreeGrid').treegrid({
			fit : true,
			fitColumns : false,
			border : false,
			idField : 'code',
			treeField : 'name',
			parentField : 'parentCode',
			remoteSort: false,
			singleSelect : false,
            checkOnSelect : true,
            selectOnCheck : true,
			nowrap : false,
			showPageList:false,
			multiple:true,
			columns : [ [ {
				field : 'monitorId',
				align:'left',
				width : 20,
				checkbox:true
			},{
				field : 'name',
				align:'left',
				width : 200
			}
			]],
			url : "${pageContext.request.contextPath}/baseinfo/moniterinfo/getMonitorTree.do",
			onLoadSuccess : function(row,data) {								
				$(this).treegrid('clearChecked');
				$(this).treegrid('clearSelections'); 
				$('#monitordiv input:checkbox').each(function(index,el){
                    el.disabled=true;
               }); 
			},
// 			toolbar: '#menuDataGridToolbar',
			loadFilter: function (data, parent) {
				var opt = $(this).data().treegrid.options;
				return treeFilter(data, opt);
			},
			onBeforeSelect: function(node) {  
                var s=$('#resTreeGrid').treegrid('getSelections');
                alert(s.length);
//                 alert(node.code);
                 //只能選擇葉子節點，不能選擇非葉子節點
                if(node.type == 'area'){
                	 layer.msg('不能選擇該區域節點',{icon: 0});
            		 return false;
                }
                
			}
	});