React Native 物理返回键问题

1.安卓back键的处理主要就是一个事件监听

BackAndroid.addEventListener('hardwareBackPress', this.onBackPressed);
BackAndroid.removeEventListener('hardwareBackPress', this.onBackPressed);

 componentWillMount() {
            if (Platform.OS == = 'android') {
                BackAndroid.addEventListener('hardwareBackPress', this.onBackAndroid);
            }
        }
 componentWillUnmount() {
            if (Platform.OS == = 'android') {
                BackAndroid.removeEventListener('hardwareBackPress', this.onBackAndroid);
            }
        }