如何在地图上获取固定位置名称？

Question

I have created an android app with CRNA, I can get the current location of the user by Expo's location API. But I can't figure out how to get the city name of a pinned location? This is my code so far:

class Map extends Component {
  constructor(props) {
    super(props);
    this.state = {
      region: {
        latitude: 41.0141977,
        longitude: 28.9638121,
        latitudeDelta: 0.1,
        longitudeDelta: 0.05,
      },
      x: {
        latitude: 41.0238343,
        longitude: 29.0335236,
      },
      regionName: "",
    }
  }

  onDragEnd(e) {
    this.setState({x: e.nativeEvent.coordinate});
  }

  onRegionChange(region) {
    this.setState({region});
  }

  render() {
    return (
      <Modal
        animationType={"slide"}
        transparent={true}
        visible={this.props.visible}
        onRequestClose={this.props.changeState}
        style={styles.modal}
      >
        <MapView
          region={this.state.region}
          onRegionChange={this.onRegionChange.bind(this)}
          style={styles.map}
        ><MapView.Marker draggable
                         coordinate={this.state.x}
                         onDragEnd={this.onDragEnd.bind(this)}

        /></MapView>
      </Modal>
    );
  }
}

Answer 1

For that you need to use some for of geocoding.

In general look at the google maps page about geocoding . And here is an npm package for react native.

Answer 2

As I googled more and more I learnt it's called reverse geocoding. So I created an redux action like this and it solved my problem very well:

 export function fetchCityName(lat, lng) {
  const link = `http://maps.googleapis.com/maps/api/geocode/json?latlng=${lat},${lng}`;
  return dispatch => {
    dispatch(startFetch());

    return fetch(link)
      .then(response => response.json())
      .then(responseJson => {
        const addressComponent = _.get(responseJson, 'results[0].address_components', []);
        const getAreaName = zone => _.get(
          addressComponent,
          `[${_.findIndex(addressComponent, obj => _.includes(obj.types, zone))}].long_name`
        );

        const region = ' ' + getAreaName('administrative_area_level_1');
        const country = ' ' + getAreaName('country');
        const region2 = getAreaName('administrative_area_level_2');

        const location = region2 ?
          [region2, region, country].toString() :
          region.concat(',' + country);

        dispatch(getCityName(location));
      })
      .catch(console.error)