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page.title=Displaying the Location Address
parent.title=Making Your App Location Aware
parent.link=index.html
trainingnavtop=true
previous.title=Obtaining the Current Location
previous.link=currentlocation.html
@jd:body
<!-- This is the training bar -->
<div id="tb-wrapper">
<div id="tb">
<h2>This lesson teaches you to</h2>
<ol>
<li><a href="geocoding.html#TaskReverseGeocoding">Perform Reverse Geocoding</a></li>
</ol>
<h2>You should also read</h2>
<ul>
<li><a href="{@docRoot}guide/topics/location/index.html">Location and Maps</a></li>
</ul>
<h2>Try it out</h2>
<div class="download-box">
<a href="http://developer.android.com/shareables/training/LocationAware.zip" class="button">Download
the sample app</a>
<p class="filename">LocationAware.zip</p>
</div>
</div>
</div>
<p>As shown in previous lessons, location updates are received in the form of latitude and longitude coordinates. While this format is useful for calculating distance or displaying a pushpin on a map, the decimal numbers make no sense to most end users. If you need to display a location to user, it is much more preferable to display the address instead.</p>
<h2 id="TaskReverseGeocoding">Perform Reverse Geocoding</h2>
<p>Reverse-geocoding is the process of translating latitude longitude coordinates to a human-readable address. The {@link android.location.Geocoder} API is available for this purpose. Note that behind the scene, the API is dependent on a web service. If such service is unavailable on the device, the API will throw a "Service not Available exception" or return an empty list of addresses. A helper method called {@link android.location.Geocoder#isPresent()} was added in Android 2.3 (API level 9) to check for the existence of the service.</p>
<p>The following code snippet demonstrates the use of the {@link android.location.Geocoder} API to perform reverse-geocoding. Since the {@link android.location.Geocoder#getFromLocation(double, double, int) getFromLocation()} method is synchronous, you should not invoke it from the UI thread, hence an {@link android.os.AsyncTask} is used in the snippet.</p>
<pre>
private final LocationListener listener = new LocationListener() {
public void onLocationChanged(Location location) {
// Bypass reverse-geocoding if the Geocoder service is not available on the
// device. The isPresent() convenient method is only available on Gingerbread or above.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD && Geocoder.isPresent()) {
// Since the geocoding API is synchronous and may take a while. You don't want to lock
// up the UI thread. Invoking reverse geocoding in an AsyncTask.
(new ReverseGeocodingTask(this)).execute(new Location[] {location});
}
}
...
};
// AsyncTask encapsulating the reverse-geocoding API. Since the geocoder API is blocked,
// we do not want to invoke it from the UI thread.
private class ReverseGeocodingTask extends AsyncTask<Location, Void, Void> {
Context mContext;
public ReverseGeocodingTask(Context context) {
super();
mContext = context;
}
@Override
protected Void doInBackground(Location... params) {
Geocoder geocoder = new Geocoder(mContext, Locale.getDefault());
Location loc = params[0];
List<Address> addresses = null;
try {
// Call the synchronous getFromLocation() method by passing in the lat/long values.
addresses = geocoder.getFromLocation(loc.getLatitude(), loc.getLongitude(), 1);
} catch (IOException e) {
e.printStackTrace();
// Update UI field with the exception.
Message.obtain(mHandler, UPDATE_ADDRESS, e.toString()).sendToTarget();
}
if (addresses != null && addresses.size() > 0) {
Address address = addresses.get(0);
// Format the first line of address (if available), city, and country name.
String addressText = String.format("%s, %s, %s",
address.getMaxAddressLineIndex() > 0 ? address.getAddressLine(0) : "",
address.getLocality(),
address.getCountryName());
// Update the UI via a message handler.
Message.obtain(mHandler, UPDATE_ADDRESS, addressText).sendToTarget();
}
return null;
}
}
</pre>
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