ext json数据解析不出来

[aelfintiger]

<script>
var cm = new Ext.grid.ColumnModel([{header:'哈哈',dataIndex:'id'},
{header:'mc',dataIndex:'name'},
{header:'ms',dataIndex:'descn'}
]);
var data ="{ root:[{ user_username:'admin',user_password:'admin','user_role:'aaa'},{ user_username:'root',user_password:'123','user_role:'aaa'}]}"

var store = new Ext.data.Store(
{
proxy: new Ext.data.MemoryProxy(data),
reader: new Ext.data.JsonReader({root:'root'},[
{name:'user_username'},
{name:'user_password'},
{name:'user_role'}
])
}
);
store.load();
var grid = new Ext.grid.GridPanel({
renderTo:'grid',
store:store,
cm:cm
})
</script>
页面只有标题，没有数据是 怎么回事？

[healer_kx]

Ext的Store没玩过，帮顶。

[aelfintiger]

var userStr = document.getElementById('userStr').value;
var cm = new Ext.grid.ColumnModel([
{header:'用户名',dataIndex:'user_username'},
{header:'密码',dataIndex:'user_password'},
{header:'权限',dataIndex:'user_role'}
]);
var store = new Ext.data.Store({
proxy: new Ext.data.MemoryProxy(userStr),
reader:new Ext.data.JsonReader({
root:'root'
},[{name:'user_username'},
{name:'user_password'},
{name:'user_role'}])
});
store.load();
var grid = new Ext.grid.GridPanel({
renderTo:'grid',
store:store,
cm:cm
});
修改以后还不行？？？