求教 extjs jsonReader问题

Question

json数据内容：[
{"Header_ID":1,"Effect_date":"2010-1-1","Description":"abcd","Type":1},
{"Header_ID":1,"Effect_date":"2010-1-1","Description":"abcd","Type":1}
]我现在是这样写的,希望获得Description和Header_ID,前一个是value后一个用作ID。但是运行页面后COMBOBOX无法显示出来，请问这个JsonReader该如何写？            var headerDesStore = new Ext.data.Store({
                proxy: new Ext.data.HttpProxy({url:'../MessageHeader/MsgHeaderService.aspx?action=List'}), 
                reader: new Ext.data.JsonReader(
                { }, 
                ['Description','Header_ID'] 
                )
            });
            headerDesStore.load();

Answer 1

var combo = new Ext.form.ComboBox({
                store: headerDesStore,
                displayField: 'Description',
                valueField: 'Header_ID',
                typeAhead: true,
                mode: 'local',
                triggerAction: 'all',
                emptyText: '選擇一個消息頭...',
                selectOnFocus: true,
                width: 135,
                displayField: "消息頭"
            });
你好，我的CB就如上面所写