RN 获取地理位置

代码：

export default class GeolocationView extends Component {
    watchID: number;

    constructor(props){
        super(props)
        this.state={
            lastPosition:''
        }
    }

    getPosition(){
        navigator.geolocation.getCurrentPosition(
            (position) => {
                var initialPosition = JSON.stringify(position);
                console.log('initialPosition:'+initialPosition)
                this.setState({initialPosition});
                alert(initialPosition);
            },
            (error) => alert(JSON.stringify(error)),
            {enableHighAccuracy: true, timeout: 20000, maximumAge: 1000}
        );
        this.watchID = navigator.geolocation.watchPosition((position) => {
            var lastPosition = JSON.stringify(position);
            this.setState({lastPosition});
        });
    }

    render() {
        return (
            <View style={styles.container}>
                <TouchableOpacity style={styles.button} onPress={() => this.getPosition()}>
                    <Text >获取定位信息,{this.state.lastPosition}</Text>
                </TouchableOpacity>
            </View>
        );
    }
}

const styles = StyleSheet.create({
    container: {
        flex: 1,
        marginTop: 200,
        alignItems: 'center',
    },
    button: {
        marginTop: 20,
        backgroundColor: '#808080',
        height: 35,
         140,
        borderRadius: 5,
        justifyContent: 'center',
        alignItems: 'center',
    },
});