index.android.js

import React, { Component } from 'react';
import { AppRegistry, StyleSheet, View, Dimensions } from 'react-native';
import MapView, { PROVIDER_GOOGLE } from 'react-native-maps';

let { width, height } = Dimensions.get('window');

const ASPECT_RATIO = width / height;
const LATITUDE = 0;
const LONGITUDE = 0;
const LATITUDE_DELTA = 0.0922;
const LONGITUDE_DELTA = LATITUDE_DELTA * ASPECT_RATIO;

export default class MapExample extends Component {

  constructor() {
    super();

    this.state = {
      region: {
        latitude: LATITUDE,
        longitude: LONGITUDE,
        latitudeDelta: LATITUDE_DELTA,
        longitudeDelta: LONGITUDE_DELTA,
      }
    };
  }

  componentDidMount() {
    navigator.geolocation.getCurrentPosition(
      position => {
        this.setState({
          region: {
            latitude: position.coords.latitude,
            longitude: position.coords.longitude,
            latitudeDelta: LATITUDE_DELTA,
            longitudeDelta: LONGITUDE_DELTA,
          }
        });
      },
    (error) => console.log(error.message),
    { enableHighAccuracy: true, timeout: 20000, maximumAge: 1000 },
    );
    this.watchID = navigator.geolocation.watchPosition(
      position => {
        this.setState({
          region: {
            latitude: position.coords.latitude,
            longitude: position.coords.longitude,
            latitudeDelta: LATITUDE_DELTA,
            longitudeDelta: LONGITUDE_DELTA,
          }
        });
      }
    );
  }

  componentWillUnmount() {
    navigator.geolocation.clearWatch(this.watchId);
  }

  render() {
    return (
      <View>
        <MapView
          provider={ PROVIDER_GOOGLE }
          style={ styles.container }
          initialRegion={{
            latitude: 39.7392,
            longitude: -104.9903,
            latitudeDelta: 0.0922,
            longitudeDelta: 0.0421,
          }}
        />
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    height: '100%',
    width: '100%',
  }
});

AppRegistry.registerComponent('MapExample', () => MapExample);