关于extjs treepanel复选框选中父节点与子节点的问题

 
extjs 如图，实现带有复选框的树,选中父节点时，选中所有子节点。取消所有子节点时，才能取消根节点。

var Fpanel = new Ext.tree.TreePanel({ 
id:'ptree', 
region:'west', 
layout:'anchor', 
border:false, 
rootVisible: false, 
root:new Ext.tree.AsyncTreeNode({}), 
listeners:{ 
"checkchange": function(node, state) { 
if (node.parentNode != null) { 
//子节点选中 
node.cascade(function(node){ 
node.attributes.checked = state; 
node.ui.checkbox.checked = state; 
return true; 
}); 
//父节点选中 
var pNode = node.parentNode; 
if (state || Fpanel.getChecked(id, pNode) == "") { 
pNode.ui.toggleCheck(state); 
pNode.attributes.checked = state; 
} 
} 
} 
} 
}); 
authorityTree(Fpanel); 
var authorityTree = function(Fpanel){ 
Ext.Ajax.request({ 
url: 'authorityTree.ashx', 
method:'get', 
success: function(request) { 
var data = Ext.util.JSON.decode(request.responseText); 
Fpanel.getRootNode().appendChild(data); 
Fpanel.getRootNode().expandChildNodes(true); 
Fpanel.expandAll(); 
}, 
failure: function() { 
Fpanel.render(); 
Ext.MessageBox.show({ 
title: '提示', 
msg: '服务器忙,请使用火狐浏览器浏览或稍后重试！', 
buttons: Ext.MessageBox.OK, 
icon: Ext.MessageBox.ERROR 
}); 
} 
}); 
}