ext.js 单选框组的值绑定不了？

前端定义了一个radiogroup，两个值，然后

items: [
                { boxLabel: i18n.quote_pricestrategy_strategy_count, name: 'strategy',
                    inputValue: '按数量', checked: true },
                { boxLabel: i18n.quote_pricestrategy_strategy_price, name: 'strategy',
                    inputValue: '按金额'}
            ],
            bind:{
                value: '{selectedObject.strategy}',
            },
            listeners: {
                change: 'onChangeStrategyType'
            },   
onChangeStrategyType: function (radiogroup,newValue){
        console.log(newValue);
        console.log(newValue.toString());

        var selectObject = this.getViewModel().get('selectedObject');
        selectObject.set('strategy');
    },

控制台输出

{strategy: '按金额'}
[object Object]
{strategy: '按数量'}
[object Object]

怎么样把这个strategy的字符串值绑定到selectObject的strategy上？

    console.log(newValue.strategy.toString());能输出字符串，但是传到后端还是[object Object]这样的字符串