Can you track background geolocation with React Native?

Problem

I’d like to be able to track a users location even when the app is no longer in the foreground (e.g. The user has switch to another app or switched to the home screen and locked their phone).

The use case would be a user tracking a run. They could open the app and press ‘start’ at the beginning of their run, then switch or minimise the app (press the home button) and lock the screen. At the end of the run they could bring the app into the foreground and press ‘stop’ and the app would tell them distance travelled on the run.

Question

Is tracking background geolocation possible on both iOS and Android using pure react native?

The react native docs on geolocation (https://facebook.github.io/react-native/docs/geolocation) are not very clear or detailed. The documented linked above eludes to background geolocation on iOS (without being fully clear) but does not mention Android.

Would it be best that I use Expo?

Answer

UPDATE 2019 EXPO 33.0.0:

Expo first deprecated it for their SDK 32.0.0 to meet app store guidelines but then reopened it in SDK 33.0.0.

Since, they have made it super easy to be able to implement background location. Use this code snippet that I used to make background geolocation work.

import React from 'react';
import { Text, TouchableOpacity } from 'react-native';
import * as TaskManager from 'expo-task-manager';
import * as Location from 'expo-location';

const LOCATION_TASK_NAME = 'background-location-task';

export default class Component extends React.Component {
  onPress = async () => {
    await Location.startLocationUpdatesAsync(LOCATION_TASK_NAME, {
      accuracy: Location.Accuracy.Balanced,
      timeInterval: 5000,
    });
  };

  render() {
    return (
      <TouchableOpacity onPress={this.onPress} style={{marginTop: 100}}>
        <Text>Enable background location</Text>
      </TouchableOpacity>
    );
  }
}

TaskManager.defineTask(LOCATION_TASK_NAME, ({ data, error }) => {
  if (error) {
    alert(error)
    // Error occurred - check `error.message` for more details.
    return;
  }
  if (data) {
    const { locations } = data; 
    alert(JSON.stringify(locations); //will show you the location object
    //lat is locations[0].coords.latitude & long is locations[0].coords.longitude
    // do something with the locations captured in the background, possibly post to your server with axios or fetch API 
  }
});

The code works like a charm. One thing to note is that you cannot use geolocation in the Expo App. However, you can use it in your standalone build. Consequently, if you want to use background geolocation you have to use this code and then do expo build:ios and upload to the appstore in order to be able to get a users background location.

Additionally, note that you must include

"UIBackgroundModes":[
          "location",
          "fetch"
        ]

In the info.plist section of your app.json file.