Ext FormPanel中的ComboBox为什么声明失效，全部变成了文本框,该怎么处理

Ext FormPanel中的ComboBox为什么声明失效，全部变成了文本框
学习Ext,做了一个FormPanel，用如下的代码添加了两个ComboBox控件

JScript code

{                name: "b_types",                xtype: "combo",                fieldLabel: "网点类型",                hiddenName: "type",                readOnly: true,                mode: "local",                displayField: "show",                valueField: "value",                triggerAction: "all",                value: "0",                store: new Ext.data.SimpleStore({                    fields: ["show", "value"],                    data: [["全功能型", "0"],["销售服务型", "1"],["交易型","2"]]                })            },{                xtype: "datefield",                name:"b_openningTime",                fieldLabel: "开业时间",                allowBlank:false,                blankText: "开业时间不允许为空"            },            new Ext.form.ComboBox({                name: "b_parents",                xtype: "combo",                fieldLabel: "上级网点",                hiddenName: "parentBranch",                readOnly: true,                mode: "local",                displayField: "show",                valueField: "value",                triggerAction: "all",                value: "0",                store: new Ext.data.SimpleStore({                    fields: ["show", "value"],                    data: [["x", "0"], ["xxx", "1"],["xxx", "2"]]                })            }),