componentWillMount() {this.getCallLog();
        if (Platform.OS === ‘android‘) {
            BackHandler.addEventListener(‘hardwareBackPress‘, this.onBackAndroid);
        }
    }

componentWillUnmount() {if (Platform.OS === ‘android‘) {
            // this.showToast(‘销毁‘);
            BackHandler.removeEventListener(‘hardwareBackPress‘, this.onBackAndroid);
        }
    }

onBackAndroid() {
        if (lastBackPressed && lastBackPressed + 2000 >= Date.now()) {
            //最近2秒内按过back键，可以退出应用。
            BackHandler.exitApp();
            return;
        }
        lastBackPressed = Date.now();
        ToastAndroid.show(‘再按一次退出应用‘,ToastAndroid.SHORT);
        return true;
    }