Extjs中获取RadioGroup的值

var radiogroup= new Ext.form.RadioGroup({
                fieldLabel : '默认计量单位',
                items : [{
                            boxLabel : '是',
                            inputValue : "1",
                            name : "radiog",
                            checked : true
                        }, {
                            boxLabel : '否',
                            name : "radiog",
                            inputValue : "2"
                        }]
            });

var _formpanel = new Ext.form.FormPanel({
        labelAlign : "right",
        labelWidth : 150,
        loadMask : true,
        frame : true,
        defaults : {
            width : 150
        },
        items : [radiogroup],
        buttonAlign : "center",
        buttons : [{
            text : "获取RadioGroup值",
            handler : function() {
                alert(_formpanel.getForm().getValues()["radiog"] );
            }
        }]
    });