Maps-based and location-based services are
compelling for mobile users. Hence let us explore the support for map services
in the Android platform in this tutorial. In the next we will build upon this and add location services
too.
Map services are provided by an external library
that includes the com.google.android.maps package. This library is not provided
as part of the standard SDK. It is provided as a Google APIs add-on to the
android SDK. For the convenience of developers, this add-on is provided as part
of the SDK on the emulator.
Before I jump into the example, let me explain
some fundamental concepts related to the Maps API.
NOTE: For using the Google Maps, you have to
obtain a Maps API key. How to obtain the key is also described towards the end
of this tutorial. This is Step 1.
Maps API add-on provides a MapActivity
class that extends the Activity class of Android. This helps is managing the
lifecycle of a MapView object that we will be using later. Our main class in
the application will be extending the MapActivity class. This class can be
treated as the default activity class whenever we deal with the Maps API.
MapView
– This is a class that extends the View and the ViewGroup classes of Android. It
provides the basic functionality expected on a Map like responding to key
presses or touch and allowing zooming etc. It also provides a controller object
that helps us manipulate the Map view programmatically. We will see how, in the
example later.
Now that we have understood the basics of the Maps
API, let us jump into the example.
Step 2: To begin with, when you create an android
project in Eclipse, instead of choosing the target name as Android 1.5, you
need to select the target as Google APIs. This ensures that the project has the
map API external libraries along with android 1.5 SDK.
Step 3: The Activity class you create this time should
not extend the standard “android.app.Activity” class but should extend the
MapActivity class about which I explained earlier.
Step 4: Apart from this, you need to add the
following tag in the AndroidManifext.xml in order to use the external library:
<uses-library android:name="com.google.android.maps" />
Step 5: Now let us declare the map view in
main.xml in layout folder. To do so, add this element in
order to display the map using MapView.
<com.google.android.maps.MapView
android:id="@+id/myGMap"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:enabled="true"
android:clickable="true"
android:apiKey="0YaGLMeMFKXrhzHL-uSYZSnqXqbGwE6kxF4VwFQ"
/>
Here the apikey should be what was generated by
you in an earlier step 1.
Step 6: In
the activity class I set the geo point on the map and set the satellite view to
false.
myMapView = (MapView) findViewById(R.id.myGMap);
geoPoint = new GeoPoint((int) (latitude * 1000000), (int) (longitude * 1000000));
myMapView.setSatellite(false);
Step 7: Now you are almost ready to go. But we
will try to do some programtic handling of the mapview. For that we need to get
a handle to the MapController object. It is done this way:
myMC = myMapView.getController();
myMC.setCenter(geoPoint);
myMC.setZoom(15);
I also set the zoom controls to be displayed with
this code.
myMapView.setBuiltInZoomControls(true);
myMapView.displayZoomControls(true);
Step 8: Add the following permissions in the
AndroidManifest.xml in order to access the maps over the internet:
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission>
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
You could execute your program now to view the map
with the fixed geopoint.
Step 9: One last step – let us add some actions to
the key presses for zooming in, zooming out, viewing the satellite view, normal
map view
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_I) {
myMapView.getController().setZoom(myMapView.getZoomLevel() + 1);
return true;
} else if (keyCode ==
KeyEvent.KEYCODE_O) {
myMapView.getController().setZoom(myMapView.getZoomLevel() - 1);
return true;
} else if (keyCode ==
KeyEvent.KEYCODE_S) {
myMapView.setSatellite(true);
return true;
} else if (keyCode ==
KeyEvent.KEYCODE_M) {
myMapView.setSatellite(false);
return true;
}
return false;
}
Now you can run the applications. The Google map
will show up with a pointer to the geo location defined in the program. You can
click on I, O, S and M for zooming in, zooming out, viewing the satellite map
or the normal map respectively.
Interesting?
The complete code is downloadable here.
Obtaining a Maps API Key:
Step 1: Locate debug.keystore on your system. It
is usually in the USER_HOME\Local Settings\Application Data\.android
folder on windows.
Step 2: Use the keytool utility to generate
certificate fingerprint (MD5). keytool utility that comes with the default JDK
installation.
C:\>keytool -list -alias
androiddebugkey -keys
tore .android\debug.keystore -storepass android -keypass android
It will getnerate a certificate fingerprint (MD5)
in this format:
Certificate fingerprint (MD5): XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX
Step 3: Go to the page
for obtaining the Maps API Key. Put
your Certificate fingerprint (MD5) And get your API key for android Google Map
application. On this page, paste the certificate fingerprint in the appropriate
form field, and click the “Generate API Key” button. This will return a Maps
API key string.
This key needs to be used along with the MapView
element declared in the XML layout file as mentioned in the tutorial above.
