Ext.treePanel选中根节点，父节点和子节点全都被勾选

items: tree = new Ext.tree.TreePanel({
               id : 'im-tree-selectdev',
               loader : new Ext.tree.TreeLoader({dataUrl : './'+xxxxx,baseParams:{action:'xxxx'}}),
               lines : false,
               autoScroll : true,
               rootVisible : false,
               root : new Ext.tree.AsyncTreeNode({
                                  nodeType : 'async',
                                  text : '',
                                  draggable : false,
                                  id : '0'
                        }),
                listeners : {
                          "checkchange": function(node, state) {
                                    node.cascade(function(node){    //cascade是有瀑布之意
                                    node.attributes.checked = state;  
                                    node.ui.checkbox.checked = state;
                                    return true;   
                                });
                               }
                             }
                          })