Extjs4的FormPanel如何动态添加表单组件

{
                        columnWidth:0.25,
                        items:[{
                            columnWidth:0.25,
                            items:[{
                                xtype: 'textfield' ,
                                maxLength:50,
                                width:150,
                                name: 'Gzzk'
                            }]
                         }]
                    }]
                },{
                    columnWidth:1,
                    layout: 'column' ,
                    style: 'padding-top:8px;padding-left:14' ,
                    layout: 'form' ,
                    labelWidth:70,
                    items:[{
                        anchor:  '45%' ,
                        allowBlank:  true ,
                        msgTarget:  'side' ,
                        xtype:  'fileuploadfield' ,
                        id:  'filepath' ,
                        name:  'filepath' ,
                        emptyText:  '请选择一个文件' ,
                        fieldLabel:  '上传文件' ,
                        buttonCfg: {
                            text:  '' ,
                            iconCls:  'upload-icon'
                        }
                    }] //itmes2 over
                },{
                    columnWidth:1,
                    style: 'padding-top:8px;padding-left:14' ,
                    items:[{
                        xtype: 'button' ,
                        text: '点击生成下一行' ,
                        handler: function (){

                            var  _panel =  this .ownerCt;

                            var  _textfield =  new  Ext.form.TextField({
                               width:150
                            });

                            _panel.add(_textfield);
                        }
                    }]
                }
            ] //items1 over
            ,buttons:[
                {
                    id: 'btnOk' ,
                    text: '确  定' ,
                    handler: function ()
                    {
                        Ext.MessageBox.show
                        (
                            {
                                msg:  '正在保存，请稍等...' ,
                                progressText:  'Saving...' ,
                                width:300,
                                wait: true ,
                                waitConfig: {interval:200},
                                icon: 'download' ,
                                animEl:  'saving'
                            }
                        );
                        fp.form.submit
                        (
                            {
                                url: '../../MyAshx/Gcglb/add/gcglb_gcxxgl_sgjs.ashx?xmid=' +xmid,
                                method: 'post' ,
                                success: function (form,action)
                                {
                                    var  flag = action.result.success;
                                    if  (flag ==  true )
                                    {
                                        Ext.MessageBox.alert( '恭喜' , '添加信息成功!' );
                                        Datas.reload();
                                        newWin.destroy();
                                    }
                                },
                                failure: function ()
                                {
                                    Ext.Msg.alert( '错误' , '服务器出现错误请稍后再试！' );
                                }
                            }
                        );
                    }
                },{
                    text: '关   闭' ,
                    handler: function ()
                    {
                        newWin.destroy();
                    }
                }
            ]
        }
    );
    newWin =  new  Ext.Window
    (
        {
            layout: 'fit' ,
            resizeHandles: 'n s' ,
            resizable : true ,
            width:740,
            closable: false ,
            height:400,
            minWidth:740,
            frame: true ,
            minHeight:400,
            collapsible: false ,
            closeAction :  'hide' ,
            autoScroll: true ,
            plain :  false ,
            modal:  'true' ,
            title :  '添加技术人员动态信息' ,
            items : fp
        }
    );
    newWin.show();

}