GeoFire for Android — Realtime location queries with Firebase

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GeoFire is an open-source library for Android that allows you to store and query a set of keys based on their geographic location.

At its heart, GeoFire simply stores locations with string keys. Its main benefit however, is the possibility of querying keys within a given geographic area - all in realtime.

GeoFire uses the Firebase Realtime Database for data storage, allowing query results to be updated in realtime as they change. GeoFire selectively loads only the data near certain locations, keeping your applications light and responsive, even with extremely large datasets.

GeoFire clients are also available for other languages:

Integrating GeoFire with your data

GeoFire is designed as a lightweight add-on to the Firebase Realtime Database. However, to keep things simple, GeoFire stores data in its own format and its own location within your Firebase database. This allows your existing data format and security rules to remain unchanged and for you to add GeoFire as an easy solution for geo queries without modifying your existing data.

Example Usage

Assume you are building an app to rate bars and you store all information for a bar, e.g. name, business hours and price range, at /bars/<bar-id>. Later, you want to add the possibility for users to search for bars in their vicinity. This is where GeoFire comes in. You can store the location for each bar using GeoFire, using the bar IDs as GeoFire keys. GeoFire then allows you to easily query which bar IDs (the keys) are nearby. To display any additional information about the bars, you can load the information for each bar returned by the query at /bars/<bar-id>.

Including GeoFire in your Android project

In order to use GeoFire in your project, you need to add the Firebase Android SDK. After that you can include GeoFire with one of the choices below.

Add a dependency for GeoFire to your app's build.gradle file.

dependencies {
    // Full GeoFire library for Realtime Database users
    implementation 'com.firebase:geofire-android:3.1.0'

    // GeoFire utililty functions for Cloud Firestore users who
    // want to implement their own geo solution, see:
    // https://firebase.google.com/docs/firestore/solutions/geoqueries
    implementation 'com.firebase:geofire-android-common:3.1.0'
}

Usage

There are two ways to use GeoFire:

  • GeoFire - an end-to-end solution for adding simple geo queries to apps using Firebase Realtime Database.
  • GeoFireUtils - a set of utilities that make it simple to build a geo query solution for any app, such as those using Cloud Firestore.

GeoFire

A GeoFire object is used to read and write geo location data to your Firebase database and to create queries. To create a new GeoFire instance you need to attach it to a Firebase database reference.

DatabaseReference ref = FirebaseDatabase.getInstance().getReference("path/to/geofire");
GeoFire geoFire = new GeoFire(ref);

Note that you can point your reference to anywhere in your Firebase database, but don't forget to setup security rules for GeoFire.

Setting location data

In GeoFire you can set and query locations by string keys. To set a location for a key simply call the setLocation method. The method is passed a key as a string and the location as a GeoLocation object containing the location's latitude and longitude:

geoFire.setLocation("firebase-hq", new GeoLocation(37.7853889, -122.4056973));

To check if a write was successfully saved on the server, you can add a GeoFire.CompletionListener to the setLocation call:

geoFire.setLocation("firebase-hq", new GeoLocation(37.7853889, -122.4056973), new GeoFire.CompletionListener() {
    @Override
    public void onComplete(String key, FirebaseError error) {
        if (error != null) {
            System.err.println("There was an error saving the location to GeoFire: " + error);
        } else {
            System.out.println("Location saved on server successfully!");
        }
    }
});

To remove a location and delete it from the database simply pass the location's key to removeLocation:

geoFire.removeLocation("firebase-hq");

Retrieving a location

Retrieving a location for a single key in GeoFire happens with callbacks:

geoFire.getLocation("firebase-hq", new LocationCallback() {
    @Override
    public void onLocationResult(String key, GeoLocation location) {
        if (location != null) {
            System.out.println(String.format("The location for key %s is [%f,%f]", key, location.latitude, location.longitude));
        } else {
            System.out.println(String.format("There is no location for key %s in GeoFire", key));
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        System.err.println("There was an error getting the GeoFire location: " + databaseError);
    }
});

Geo Queries

GeoFire allows you to query all keys within a geographic area using GeoQuery objects. As the locations for keys change, the query is updated in realtime and fires events letting you know if any relevant keys have moved. GeoQuery parameters can be updated later to change the size and center of the queried area.

// creates a new query around [37.7832, -122.4056] with a radius of 0.6 kilometers
GeoQuery geoQuery = geoFire.queryAtLocation(new GeoLocation(37.7832, -122.4056), 0.6);

Receiving events for geo queries

Key Events

There are five kinds of "key" events that can occur with a geo query:

  1. Key Entered: The location of a key now matches the query criteria.
  2. Key Exited: The location of a key no longer matches the query criteria.
  3. Key Moved: The location of a key changed but the location still matches the query criteria.
  4. Query Ready: All current data has been loaded from the server and all initial events have been fired.
  5. Query Error: There was an error while performing this query, e.g. a violation of security rules.

Key entered events will be fired for all keys initially matching the query as well as any time afterwards that a key enters the query. Key moved and key exited events are guaranteed to be preceded by a key entered event.

Sometimes you want to know when the data for all the initial keys has been loaded from the server and the corresponding events for those keys have been fired. For example, you may want to hide a loading animation after your data has fully loaded. This is what the "ready" event is used for.

Note that locations might change while initially loading the data and key moved and key exited events might therefore still occur before the ready event is fired.

When the query criteria is updated, the existing locations are re-queried and the ready event is fired again once all events for the updated query have been fired. This includes key exited events for keys that no longer match the query.

To listen for events you must add a GeoQueryEventListener to the GeoQuery:

geoQuery.addGeoQueryEventListener(new GeoQueryEventListener() {
    @Override
    public void onKeyEntered(String key, GeoLocation location) {
        System.out.println(String.format("Key %s entered the search area at [%f,%f]", key, location.latitude, location.longitude));
    }

    @Override
    public void onKeyExited(String key) {
        System.out.println(String.format("Key %s is no longer in the search area", key));
    }

    @Override
    public void onKeyMoved(String key, GeoLocation location) {
        System.out.println(String.format("Key %s moved within the search area to [%f,%f]", key, location.latitude, location.longitude));
    }

    @Override
    public void onGeoQueryReady() {
        System.out.println("All initial data has been loaded and events have been fired!");
    }

    @Override
    public void onGeoQueryError(DatabaseError error) {
        System.err.println("There was an error with this query: " + error);
    }
});

You can call either removeGeoQueryEventListener to remove a single event listener or removeAllListeners to remove all event listeners for a GeoQuery.

Data Events

If you are storing model data and geo data in the same database location, you may want access to the DataSnapshot as part of geo events. In this case, use a GeoQueryDataEventListener rather than a key listener.

These "data event" listeners have all of the same events as the key listeners with one additional event type:

  1. Data Changed: the underlying DataSnapshot has changed. Every "data moved" event is followed by a data changed event but you can also get change events without a move if the data changed does not affect the location.

Adding a data event listener is similar to adding a key event listener:

geoQuery.addGeoQueryDataEventListener(new GeoQueryDataEventListener() {

  @Override
  public void onDataEntered(DataSnapshot dataSnapshot, GeoLocation location) {
    // ...
  }

  @Override
  public void onDataExited(DataSnapshot dataSnapshot) {
    // ...
  }

  @Override
  public void onDataMoved(DataSnapshot dataSnapshot, GeoLocation location) {
    // ...
  }

  @Override
  public void onDataChanged(DataSnapshot dataSnapshot, GeoLocation location) {
    // ...
  }

  @Override
  public void onGeoQueryReady() {
    // ...
  }

  @Override
  public void onGeoQueryError(DatabaseError error) {
    // ...
  }

});

Updating the query criteria

The GeoQuery search area can be changed with setCenter and setRadius. Key exited and key entered events will be fired for keys moving in and out of the old and new search area, respectively. No key moved events will be fired; however, key moved events might occur independently.

Updating the search area can be helpful in cases such as when you need to update the query to the new visible map area after a user scrolls.

GeoFireUtils

The geofire-android-common library provides the GeoFireUtils class which contains utilities for working with geohashes but has no dependency on or integration with a specific database. The GeoFireUtils class contains the following utility methods:

  • String getGeoHashForLocation(@NonNull GeoLocation location) - compute the geohash string for a given (lat,lng) par with default precision.
  • String getGeoHashForLocation(@NonNull GeoLocation location, int precision) - compute the geohash string for a given (lat, lng) pair with custom precision.
  • double getDistanceBetween(@NonNull GeoLocation a, @NonNull GeoLocation b) - compute the distance, in kilometers, between two locations.
  • List<GeoQueryBounds> getGeoHashQueryBounds(@NonNull GeoLocation location, double radius) - given a center point and a radius distance, compute a set of query bounds that can be joined to find all points within the radius distance of the center.

For a detailed guide on how to use these utilities to add geo querying capabilities to your Cloud Firestore app, see: https://firebase.google.com/docs/firestore/solutions/geoqueries

Publishing

Credentials

The library is published to Maven Central by the firebase-sonatype account, Googlers can find the password for this account in Valentine

GPG Key

You will need to create a private GPG keyring on your machine, if you don't have one do the following steps:

  1. Run gpg --full-generate-key
  2. Choose RSA and RSA for the key type
  3. Use 4096 for the key size
  4. Use 0 for the expiration (never)
  5. Use any name, email address, and password

This creates your key in ~/.gnupg/openpgp-revocs.d/ with .rev format. The last 8 characters before the .rev extension are your Key ID.

To export the key, run:

gpg --export-secret-keys -o $HOME/sonatype.gpg

Finally upload your key to the keyserver:

gpg --keyserver hkp://keys.openpgp.org --send-keys <YOUR KEY ID>

Local Properties

Open your $HOME/.gradle/gradle.properties file at and fill in the values:

signing.keyId=<KEY ID>
signing.password=<PASSWORD YOU CHOSE>
signing.secretKeyRingFile=<FULL PATH TO YOUR GPG FILE>
mavenCentralRepositoryUsername=firebase-sonatype
mavenCentralRepositoryUsername=<PASSWORD FROM VALENTINE>

Publish

To publish, run:

./gradlew publish

Release

Follow the instructions here:

  1. Navigate to https://oss.sonatype.org/ and Log In
  2. On the left side click Build Promotion and look for the com.firebase repo
  3. Click Close ... wait a few minutes (you can check status with Refresh)
  4. Click Release