GeofencingScreen.js

import { Notifications } from 'expo';
import * as Location from 'expo-location';
import * as Permissions from 'expo-permissions';
import * as TaskManager from 'expo-task-manager';
import React from 'react';
import { AppState, Platform, StyleSheet, Text, View } from 'react-native';
import MapView from 'react-native-maps';
import { NavigationEvents } from 'react-navigation';
import { MaterialIcons } from '@expo/vector-icons';

import Button from '../components/PrimaryButton';

const GEOFENCING_TASK = 'geofencing';
const REGION_RADIUSES = [30, 50, 75, 100, 150, 200];

export default class GeofencingScreen extends React.Component {
  static navigationOptions = {
    title: 'Geofencing',
  };

  mapViewRef = React.createRef();

  state = {
    isGeofencing: false,
    newRegionRadius: REGION_RADIUSES[1],
    geofencingRegions: [],
    initialRegion: null,
    error: null,
  };

  didFocus = async () => {
    let { status } = await Permissions.askAsync(Permissions.LOCATION);

    if (status !== 'granted') {
      AppState.addEventListener('change', this.handleAppStateChange);
      this.setState({
        error:
          'Location permissions are required in order to use this feature. You can manually enable them at any time in the "Location Services" section of the Settings app.',
      });
      return;
    } else {
      this.setState({ error: null });
    }

    const { coords } = await Location.getCurrentPositionAsync();
    const isGeofencing = await Location.hasStartedGeofencingAsync(GEOFENCING_TASK);
    const geofencingRegions = await getSavedRegions();

    if (!isGeofencing) {
      alert(
        'Tap on the map to select a region with chosen radius and then press `Start geofencing` to start getting geofencing notifications.'
      );
    }

    this.setState({
      isGeofencing,
      geofencingRegions,
      initialRegion: {
        latitude: coords.latitude,
        longitude: coords.longitude,
        latitudeDelta: 0.004,
        longitudeDelta: 0.002,
      },
    });
  };

  handleAppStateChange = nextAppState => {
    if (nextAppState !== 'active') {
      return;
    }

    if (this.state.initialRegion) {
      AppState.removeEventListener('change', this.handleAppStateChange);
      return;
    }

    this.didFocus();
  };

  canToggleGeofencing() {
    return this.state.isGeofencing || this.state.geofencingRegions.length > 0;
  }

  toggleGeofencing = async () => {
    if (!this.canToggleGeofencing()) {
      return;
    }

    if (this.state.isGeofencing) {
      await Location.stopGeofencingAsync(GEOFENCING_TASK);
      this.setState({ geofencingRegions: [] });
    } else {
      await Location.startGeofencingAsync(GEOFENCING_TASK, this.state.geofencingRegions);
      alert(
        'You will be receiving notifications when the device enters or exits from selected regions.'
      );
    }
    this.setState(state => ({ isGeofencing: !state.isGeofencing }));
  };

  shiftRegionRadius = () => {
    const index = REGION_RADIUSES.indexOf(this.state.newRegionRadius) + 1;
    const radius = index < REGION_RADIUSES.length ? REGION_RADIUSES[index] : REGION_RADIUSES[0];

    this.setState({ newRegionRadius: radius });
  };

  centerMap = async () => {
    const { coords } = await Location.getCurrentPositionAsync();
    const mapView = this.mapViewRef.current;

    if (mapView) {
      mapView.animateToRegion({
        latitude: coords.latitude,
        longitude: coords.longitude,
        latitudeDelta: 0.004,
        longitudeDelta: 0.002,
      });
    }
  };

  onMapPress = ({ nativeEvent: { coordinate } }) => {
    this.setState(
      state => ({
        geofencingRegions: [
          ...state.geofencingRegions,
          {
            identifier: `${coordinate.latitude},${coordinate.longitude}`,
            latitude: coordinate.latitude,
            longitude: coordinate.longitude,
            radius: state.newRegionRadius,
          },
        ],
      }),
      async () => {
        if (await Location.hasStartedGeofencingAsync(GEOFENCING_TASK)) {
          // update existing geofencing task
          await Location.startGeofencingAsync(GEOFENCING_TASK, this.state.geofencingRegions);
        }
      }
    );
  };

  renderRegions() {
    const { geofencingRegions } = this.state;

    return geofencingRegions.map(region => {
      return (
        <MapView.Circle
          key={region.identifier}
          center={region}
          radius={region.radius}
          strokeColor="rgba(78,155,222,0.8)"
          fillColor="rgba(78,155,222,0.2)"
        />
      );
    });
  }

  getGeofencingButtonContent() {
    const canToggle = this.canToggleGeofencing();

    if (canToggle) {
      return this.state.isGeofencing ? 'Stop geofencing' : 'Start geofencing';
    }
    return 'Select at least one region on the map';
  }

  render() {
    if (this.state.error) {
      return <Text style={styles.errorText}>{this.state.error}</Text>;
    }

    if (!this.state.initialRegion) {
      return <NavigationEvents onDidFocus={this.didFocus} />;
    }

    const canToggle = this.canToggleGeofencing();

    return (
      <View style={styles.screen}>
        <MapView
          ref={this.mapViewRef}
          style={styles.mapView}
          initialRegion={this.state.initialRegion}
          onPress={this.onMapPress}
          showsUserLocation>
          {this.renderRegions()}
        </MapView>

        <View style={styles.buttons} pointerEvents="box-none">
          <View style={styles.topButtons}>
            <View style={styles.buttonsColumn}>
              <Button style={styles.button} onPress={this.shiftRegionRadius}>
                Radius: {this.state.newRegionRadius}m
              </Button>
            </View>
            <View style={styles.buttonsColumn}>
              <Button style={styles.button} onPress={this.centerMap}>
                <MaterialIcons name="my-location" size={20} color="white" />
              </Button>
            </View>
          </View>

          <View style={styles.bottomButtons}>
            <Button
              style={[styles.button, canToggle ? null : styles.disabledButton]}
              onPress={this.toggleGeofencing}>
              {this.getGeofencingButtonContent()}
            </Button>
          </View>
        </View>
      </View>
    );
  }
}

async function getSavedRegions() {
  const tasks = await TaskManager.getRegisteredTasksAsync();
  const task = tasks.find(({ taskName }) => taskName === GEOFENCING_TASK);
  return task ? task.options.regions : [];
}

if (Platform.OS !== 'android') {
  TaskManager.defineTask(GEOFENCING_TASK, async ({ data: { region } }) => {
    const stateString = Location.GeofencingRegionState[region.state].toLowerCase();
    const body = `You're ${stateString} a region with latitude: ${region.latitude}, longitude: ${region.longitude} and radius: ${region.radius}m`;

    await Notifications.presentLocalNotificationAsync({
      title: 'Expo Geofencing',
      body,
      data: {
        ...region,
        notificationBody: body,
        notificationType: GEOFENCING_TASK,
      },
    });
  });
}

Notifications.addListener(({ data, remote }) => {
  if (!remote && data.notificationType === GEOFENCING_TASK) {
    alert(data.notificationBody);
  }
});

const styles = StyleSheet.create({
  screen: {
    flex: 1,
  },
  mapView: {
    flex: 1,
  },
  buttons: {
    flex: 1,
    flexDirection: 'column',
    justifyContent: 'space-between',
    padding: 10,
    position: 'absolute',
    top: 0,
    right: 0,
    bottom: 0,
    left: 0,
  },
  topButtons: {
    flexDirection: 'row',
    justifyContent: 'space-between',
  },
  bottomButtons: {
    flexDirection: 'column',
    alignItems: 'flex-end',
  },
  buttonsColumn: {
    flexDirection: 'column',
    alignItems: 'flex-start',
  },
  button: {
    paddingVertical: 5,
    paddingHorizontal: 10,
    marginVertical: 5,
  },
  disabledButton: {
    backgroundColor: 'gray',
    opacity: 0.8,
  },
  errorText: {
    fontSize: 15,
    color: 'rgba(0,0,0,0.7)',
    margin: 20,
  },
});