Displaying a Location Address

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The lessons Getting the Last Known Location and Receiving Location Updates describe how to get the user's location in the form of a Location object that contains latitude and longitude coordinates. Although latitude and longitude are useful for calculating distance or displaying a map position, in many cases the address of the location is more useful. For example, if you want to let your users know where they are or what is close by, a street address is more meaningful than the geographic coordinates (latitude/longitude) of the location.

Using the Geocoder class in the Android framework location APIs, you can convert an address to the corresponding geographic coordinates. This process is called geocoding. Alternatively, you can convert a geographic location to an address. The address lookup feature is also known as reverse geocoding.

This lesson shows you how to use the getFromLocation() method to convert a geographic location to an address. The method returns an estimated street address corresponding to a given latitude and longitude.

Get a Geographic Location

The last known location of the device is a useful starting point for the address lookup feature. The lesson on Getting the Last Known Location shows you how to use the getLastLocation() method provided by the fused location provider to find the latest location of the device.

To access the fused location provider, you need to create an instance of the Google Play services API client. To learn how to connect your client, see Connect to Google Play Services.

In order for the fused location provider to retrieve a precise street address, set the location permission in your app manifest to ACCESS_FINE_LOCATION, as shown in the following example:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.google.android.gms.location.sample.locationupdates" >

  <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
</manifest>

Define an Intent Service to Fetch the Address

The getFromLocation() method provided by the Geocoder class accepts a latitude and longitude, and returns a list of addresses. The method is synchronous, and may take a long time to do its work, so you should not call it from the main, user interface (UI) thread of your app.

The IntentService class provides a structure for running a task on a background thread. Using this class, you can handle a long-running operation without affecting your UI's responsiveness. Note that the AsyncTask class also allows you to perform background operations, but it's designed for short operations. An AsyncTask shouldn't keep a reference to the UI if the activity is recreated, for example when the device is rotated. In contrast, an IntentService doesn't need to be cancelled when the activity is rebuilt.

Define a FetchAddressIntentService class that extends IntentService. This class is your address lookup service. The intent service handles an intent asynchronously on a worker thread, and stops itself when it runs out of work. The intent extras provide the data needed by the service, including a Location object for conversion to an address, and a ResultReceiver object to handle the results of the address lookup. The service uses a Geocoder to fetch the address for the location, and sends the results to the ResultReceiver.

Define the Intent Service in your App Manifest

Add an entry to your app manifest defining the intent service:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.google.android.gms.location.sample.locationaddress" >
    <application
        ...
        <service
            android:name=".FetchAddressIntentService"
            android:exported="false"/>
    </application>
    ...
</manifest>

Note: The <service> element in the manifest doesn't need to include an intent filter, because your main activity creates an explicit intent by specifying the name of the class to use for the intent.

Create a Geocoder

The process of converting a geographic location to an address is called reverse geocoding. To perform the main work of the intent service, that is, your reverse geocoding request, implement onHandleIntent() within the FetchAddressIntentService class. Create a Geocoder object to handle the reverse geocoding.

A locale represents a specific geographical or linguistic region. Locale objects are used to adjust the presentation of information, such as numbers or dates, to suit the conventions in the region represented by the locale. Pass a Locale object to the Geocoder object, to ensure that the resulting address is localized to the user's geographic region.

@Override
protected void onHandleIntent(Intent intent) {
    Geocoder geocoder = new Geocoder(this, Locale.getDefault());
    ...
}

Retrieve the street address data

The next step is to retrieve the street address from the geocoder, handle any errors that may occur, and send the results back to the activity that requested the address. To report the results of the geocoding process, you need two numeric constants that indicate success or failure. Define a Constants class to contain the values, as shown in this code snippet:

public final class Constants {
    public static final int SUCCESS_RESULT = 0;
    public static final int FAILURE_RESULT = 1;
    public static final String PACKAGE_NAME =
        "com.google.android.gms.location.sample.locationaddress";
    public static final String RECEIVER = PACKAGE_NAME + ".RECEIVER";
    public static final String RESULT_DATA_KEY = PACKAGE_NAME +
        ".RESULT_DATA_KEY";
    public static final String LOCATION_DATA_EXTRA = PACKAGE_NAME +
        ".LOCATION_DATA_EXTRA";
}

To get a street address corresponding to a geographical location, call getFromLocation(), passing it the latitude and longitude from the location object, and the maximum number of addresses you want returned. In this case, you want just one address. The geocoder returns an array of addresses. If no addresses were found to match the given location, it returns an empty list. If there is no backend geocoding service available, the geocoder returns null.

Check for the following errors as shown in the code sample below. If an error occurs, place the corresponding error message in the errorMessage variable, so you can send it back to the requesting activity:

  • No location data provided - The intent extras do not include the Location object required for reverse geocoding.
  • Invalid latitude or longitude used - The latitude and/or longitude values provided in the Location object are invalid.
  • No geocoder available - The background geocoding service is not available, due to a network error or IO exception.
  • Sorry, no address found - The geocoder could not find an address for the given latitude/longitude.

To get the individual lines of an address object, use the getAddressLine() method provided by the Address class. Then join the lines into a list of address fragments ready to return to the activity that requested the address.

To send the results back to the requesting activity, call the deliverResultToReceiver() method (defined in Return the address to the requestor). The results consist of the previously-mentioned numeric success/failure code and a string. In the case of a successful reverse geocoding, the string contains the address. In the case of a failure, the string contains the error message, as shown in the code sample below:

@Override
protected void onHandleIntent(Intent intent) {
    String errorMessage = "";

    // Get the location passed to this service through an extra.
    Location location = intent.getParcelableExtra(
            Constants.LOCATION_DATA_EXTRA);

    ...

    List<Address> addresses = null;

    try {
        addresses = geocoder.getFromLocation(
                location.getLatitude(),
                location.getLongitude(),
                // In this sample, get just a single address.
                1);
    } catch (IOException ioException) {
        // Catch network or other I/O problems.
        errorMessage = getString(R.string.service_not_available);
        Log.e(TAG, errorMessage, ioException);
    } catch (IllegalArgumentException illegalArgumentException) {
        // Catch invalid latitude or longitude values.
        errorMessage = getString(R.string.invalid_lat_long_used);
        Log.e(TAG, errorMessage + ". " +
                "Latitude = " + location.getLatitude() +
                ", Longitude = " +
                location.getLongitude(), illegalArgumentException);
    }

    // Handle case where no address was found.
    if (addresses == null || addresses.size()  == 0) {
        if (errorMessage.isEmpty()) {
            errorMessage = getString(R.string.no_address_found);
            Log.e(TAG, errorMessage);
        }
        deliverResultToReceiver(Constants.FAILURE_RESULT, errorMessage);
    } else {
        Address address = addresses.get(0);
        ArrayList<String> addressFragments = new ArrayList<String>();

        // Fetch the address lines using getAddressLine,
        // join them, and send them to the thread.
        for(int i = 0; i < address.getMaxAddressLineIndex(); i++) {
            addressFragments.add(address.getAddressLine(i));
        }
        Log.i(TAG, getString(R.string.address_found));
        deliverResultToReceiver(Constants.SUCCESS_RESULT,
                TextUtils.join(System.getProperty("line.separator"),
                        addressFragments));
    }
}

Return the address to the requestor

The final thing the intent service must do is send the address back to a ResultReceiver in the activity that started the service. The ResultReceiver class allows you to send a numeric result code as well as a message containing the result data. The numeric code is useful for reporting the success or failure of the geocoding request. In the case of a successful reverse geocoding, the message contains the address. In the case of a failure, the message contains some text describing the reason for failure.

You have already retrieved the address from the geocoder, trapped any errors that may occur, and called the deliverResultToReceiver() method. Now you need to define the deliverResultToReceiver() method that sends a result code and message bundle to the result receiver.

For the result code, use the value that you've passed to the deliverResultToReceiver() method in the resultCode parameter. To construct the message bundle, concatenate the RESULT_DATA_KEY constant from your Constants class (defined in Retrieve the street address data) and the value in the message parameter passed to the deliverResultToReceiver() method, as shown in the following sample: 

public class FetchAddressIntentService extends IntentService {
    protected ResultReceiver mReceiver;
    ...
    private void deliverResultToReceiver(int resultCode, String message) {
        Bundle bundle = new Bundle();
        bundle.putString(Constants.RESULT_DATA_KEY, message);
        mReceiver.send(resultCode, bundle);
    }
}

Start the Intent Service

The intent service, as defined in the previous section, runs in the background and is responsible for fetching the address corresponding to a given geographic location. When you start the service, the Android framework instantiates and starts the service if it isn't already running, and creates a process if needed. If the service is already running then it remains running. Because the service extends IntentService, it shuts down automatically when all intents have been processed.

Start the service from your app's main activity, and create an Intent to pass data to the service. You need an explicit intent, because you want only your service to respond to the intent. For more information, see Intent Types.

To create an explicit intent, specify the name of the class to use for the service: FetchAddressIntentService.class. Pass two pieces of information in the intent extras:

  • A ResultReceiver to handle the results of the address lookup.
  • A Location object containing the latitude and longitude that you want to convert to an address.

The following code sample shows you how to start the intent service:

public class MainActivity extends ActionBarActivity implements
        ConnectionCallbacks, OnConnectionFailedListener {

    protected Location mLastLocation;
    private AddressResultReceiver mResultReceiver;
    ...

    protected void startIntentService() {
        Intent intent = new Intent(this, FetchAddressIntentService.class);
        intent.putExtra(Constants.RECEIVER, mResultReceiver);
        intent.putExtra(Constants.LOCATION_DATA_EXTRA, mLastLocation);
        startService(intent);
    }
}

Call the above startIntentService() method when the user takes an action that requires a geocoding address lookup. For example, the user may press a Fetch address button on your app's UI. Before starting the intent service, you need to check that the connection to Google Play services is present. The following code snippet shows the call to the startIntentService() method in the button handler:

public void fetchAddressButtonHandler(View view) {
    // Only start the service to fetch the address if GoogleApiClient is
    // connected.
    if (mGoogleApiClient.isConnected() && mLastLocation != null) {
        startIntentService();
    }
    // If GoogleApiClient isn't connected, process the user's request by
    // setting mAddressRequested to true. Later, when GoogleApiClient connects,
    // launch the service to fetch the address. As far as the user is
    // concerned, pressing the Fetch Address button
    // immediately kicks off the process of getting the address.
    mAddressRequested = true;
    updateUIWidgets();
}

You must also start the intent service when the connection to Google Play services is established, if the user has already clicked the button on your app's UI. The following code snippet shows the call to the startIntentService() method in the onConnected() callback provided by the Google API Client:

public class MainActivity extends ActionBarActivity implements
        ConnectionCallbacks, OnConnectionFailedListener {
    ...
    @Override
    public void onConnected(Bundle connectionHint) {
        // Gets the best and most recent location currently available,
        // which may be null in rare cases when a location is not available.
        mLastLocation = LocationServices.FusedLocationApi.getLastLocation(
                mGoogleApiClient);

        if (mLastLocation != null) {
            // Determine whether a Geocoder is available.
            if (!Geocoder.isPresent()) {
                Toast.makeText(this, R.string.no_geocoder_available,
                        Toast.LENGTH_LONG).show();
                return;
            }

            if (mAddressRequested) {
                startIntentService();
            }
        }
    }
}

Receive the Geocoding Results

The intent service has handled the geocoding request, and uses a ResultReceiver to return the results to the activity that made the request. In the activity that makes the request, define an AddressResultReceiver that extends ResultReceiver to handle the response from FetchAddressIntentService.

The result includes a numeric result code (resultCode) as well as a message containing the result data (resultData). If the reverse geocoding process was successful, the resultData contains the address. In the case of a failure, the resultData contains text describing the reason for failure. For details of the possible errors, see Return the address to the requestor.

Override the onReceiveResult() method to handle the results delivered to the result receiver, as shown in the following code sample:

public class MainActivity extends ActionBarActivity implements
        ConnectionCallbacks, OnConnectionFailedListener {
    ...
    class AddressResultReceiver extends ResultReceiver {
        public AddressResultReceiver(Handler handler) {
            super(handler);
        }

        @Override
        protected void onReceiveResult(int resultCode, Bundle resultData) {

            // Display the address string
            // or an error message sent from the intent service.
            mAddressOutput = resultData.getString(Constants.RESULT_DATA_KEY);
            displayAddressOutput();

            // Show a toast message if an address was found.
            if (resultCode == Constants.SUCCESS_RESULT) {
                showToast(getString(R.string.address_found));
            }

        }
    }
}
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