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。

复制代码代码如下:

 
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 
}); 
} 
}); 
} 