This document discusses building an Android chat app using Google Cloud Platform services including Cloud Datastore, authentication, and push notifications. It provides steps to create a backend using Mobile Backend Starter, generate client IDs, access APIs with and without authentication, add push notifications using Google Cloud Messaging, and discusses app architecture considerations.

2. Android chat in the cloud
RESTful APIs, authentication, push notifications and some additional goodies
Alfredo Morresi
Developer Relations @ Google

3. Who I am
Alfredo Morresi
ROLE
Developer Relations Program Manager
COUNTRY
Italy
PASSIONS
Community, Development,
Snowboarding, Tiramisu'
REACH ME
alfredomorresi@google.com
plus.google.com/+AlfredoMorresi
@rainbowbreeze

4. Let’s start with the chat demo app
Download from https://play.google.com/store/apps/details?id=org.alexismp.cloud.backend

5. In less than 40 minutes?

6. Forget about the backend!

7. Use Google Cloud Platform + Mobile Backend Starter
Optional server-side coding: Control your cloud service using Android and iOS client libraries.
Cloud Datastore: Store millions of objects in the cloud and manage them from your app.
Push Notifications: Send and broadcast objects as messages via Apple Push Notifications and
Google Cloud Messaging.
Event Driven Programming: Create real-time interactive user experiences using Continuous
Queries.
User authentication: Authenticate users using Google Accounts and control access on private data.
Built to scale: Mobile backend runs on App Engine infrastructure to scale to millions of users within
hours.

8. Create your backend
https://developers.google.com/cloud/samples/mbs

9. Create your backend

10. Create your backend

11. Create your backend

12. Download Android app source code
http://goo.gl/0FLRPp

13. Set some values in the source and you’ve done!
Change
●
●
●
PROJECT_ID
PROJECT_NUMBER
WEB_CLIENT_ID

15. Step 1
Accessing to the APIs

16. Google Cloud Endpoints: generate APIs from annotations
https://developers.google.com/appengine/docs/java/endpoints/

17. Explore the backend APIs
Explore the APIs:
http://<YOUR_PROJECT_ID>.appspot.com/_ah/api/explorer

18. Set Open authentication in the backend

19. Access to RESTful APIs, no authentication
Set the Consts.IS_AUTH_ENABLED to false
Set the Consts.PROJECT_ID to

20. It was easy!

21. Access to RESTful APIs, no authentication
Google Cloud Endpoints automatically generates the
Android code required to access the backend APIs
Mobilebackend.Builder builder = new Mobilebackend.Builder(
AndroidHttp.newCompatibleTransport(),
new GsonFactory(),
null);
Mobilebackend backend =
builder.setRootUrl(Consts.ENDPOINT_ROOT_URL).build();

22. Access to RESTful APIs, no authentication
Insert a new CloudEntity in the backend
CloudEntity post = new CloudEntity("Guestbook");
post.put("message", "Your message here...");
EntityDto resultEntityDto = backend.endpointV1()
.insert(post.getKindName(), post.getEntityDto()).execute();
CloudEntity resultCo =
CloudEntity.createCloudEntityFromEntityDto
(resultEntityDto);
Log.i(Consts.TAG, "insert: inserted: " + resultCo);

23. Step 2
Accessing to the APIs with authentication

24. Authenticated access to the APIs
Restrict the API access only to your application(s).
ANDROID Client_ID: identifies your app in unique
way (package name + SHA1 of signing key of the app)
WEB Client_ID: establishes that the client and the
server are from the same developer so the standard
OAuth2 prompt is avoided (no 3rd party app). It’s a
shared token.
https://developers.google.com/appengine/docs/java/endpoints/auth

25. Generate Android Client ID

26. Generate Android Client ID

27. Generate Web Client ID

28. Generate Web Client ID

29. Set Android and Web Client IDs in the backend

30. Authenticated access to the APIs
Set the Consts.IS_AUTH_ENABLED to true
Set the Consts.WEB_CLIENT_ID to Web Client ID

32. The Android client provides credentials!
GoogleAccountCredential credential =
GoogleAccountCredential.usingAudience(
getActivity(), Consts.AUTH_AUDIENCE);
if (credential.getSelectedAccountName() == null) {
startActivityForResult(
credential.newChooseAccountIntent(),
REQUEST_ACCOUNT_PICKER);
String accountName =
data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
credential.setSelectedAccountName(accountName);
https://developers.google.
com/appengine/docs/java/endpoints/consume_android#Java_Making_aut
henticated_calls

33. Authenticated access to the APIs
Inject the credential in the backend manager class
// check if credential has account name
final GoogleAccountCredential gac =
credential == null || credential.getSelectedAccountName() == null
? null
: mCredential;
// create HttpRequestInitializer
HttpRequestInitializer httpRequestInitializer = new HttpRequestInitializer() {
@Override
public void initialize(HttpRequest request) throws IOException {
if (gac != null) {
gac.initialize(request);
}
}
};

34. Authenticated access to the APIs
Mobilebackend.Builder builder = new Mobilebackend.Builder(
AndroidHttp.newCompatibleTransport(),
new GsonFactory(),
httpRequestInitializer);
Mobilebackend backend =
builder.setRootUrl(Consts.ENDPOINT_ROOT_URL).build();
… Now
the API backend framework automatically
authenticates the user and enforces the authorized
clientIds whitelist, ultimately by supplying a valid
User to the API parameters.

35. Step 3
Add push notifications

37. Google Cloud Messaging for Android
http://developer.android.com/google/gcm/index.html

38. Enable GCM in the project

39. Generate a Server API Key

40. Generate a Server API Key

41. Enable GCM in the backend

42. Enable GCM in the client
Set the Consts.PROJECT_NUMBER to

44. A look into GCM client code
http://developer.android.com/google/gcm/client.html
Register your app and store registration ID
String regId = getRegIdFromPref();
if (registrationId.isEmpty()) {
regid = GoogleCloudMessaging.getInstance(context)
.register(PROJECT_ID);
storeRegIdToPref(regId);
}

45. Create a BroadcastReceiver to receive push messages
@Override
public void onReceive(Context context, Intent intent) {
// Explicitly specify that GcmIntentService will handle the intent
ComponentName comp =
new ComponentName(
context.getPackageName(),
GCMIntentService.class.getName());
// Start service, keeping the device awake while it is launching
startWakefulService(context, (intent.setComponent(comp)));
setResultCode(Activity.RESULT_OK);
}

46. Handle the message with a Service
protected void onHandleIntent(Intent intent) {
Bundle extras = intent.getExtras();
GoogleCloudMessaging gcm = GoogleCloudMessaging.getInstance(this);
String msgType = gcm.getMessageType(intent);
if (extras.isEmpty()) { // has effect of unparcelling Bundle
…
}
if (GoogleCloudMessaging.MESSAGE_TYPE_MESSAGE.equals(messageType)) {
…
}
// Release the wake lock provided by the WakefulBroadcastReceiver.
GCMBroadcastReceiver.completeWakefulIntent(intent);
}

47. And remember to...
App registration is a network operation

48. Bonus Step
App internal architecture

49. Because API calls are slow...
EntityDto resultEntityDto = backend.endpointV1()
.insert(post.getKindName(), post.getEntityDto()).execute();

50. Never forget!

51. CloudBackendASync extends CloudBackend
// create a response handler that will receive the result or an error
CloudCallbackHandler<List<CloudEntity>> handler =
new CloudCallbackHandler<List<CloudEntity>>() {
@Override
public void onComplete(List<CloudEntity> results) {
...
}
@Override
public void onError(IOException exception) {
...
}

52. CloudBackendASync extends CloudBackend
// execute the query with the handler
mProcessingFragment.getCloudBackend().listByKind(
"Guestbook",
CloudEntity.PROP_CREATED_AT,
Order.DESC,
50,
Scope.FUTURE_AND_PAST, handler);

53. Why these two classes?
Separate the logic
(CloudBackend) from the sync
management
(CloudBackendAsync) makes
the code more testable!

54. Activity lifecycle (you can do better!)
// Check to see if we have retained the fragment which handles asynchronous backend calls
mProcessingFragment = (CloudBackendFragment) mFragmentManager.
findFragmentByTag(PROCESSING_FRAGMENT_TAG);
// If not retained (or first time running), create a new one
if (mProcessingFragment == null) {
mProcessingFragment = new CloudBackendFragment();
mProcessingFragment.setRetainInstance(true);
fragmentTransaction.add(mProcessingFragment, PROCESSING_FRAGMENT_TAG);
}
…
// execute the insertion with the handler
mProcessingFragment.getCloudBackend().insert(newPost, handler);
mMessageTxt.setEnabled(false);
mSendBtn.setEnabled(false);

55. Extends the data
CloudEntity post = new CloudEntity("Guestbook");
post.put("message", "Your message here...");
post.put("alf_property", "Custom property value here...");
EntityDto resultEntityDto = backend.endpointV1()
.insert(post.getKindName(), post.getEntityDto()).execute();
CloudEntity resultCo =
CloudEntity.createCloudEntityFromEntityDto(resultEntityDto);

56. Curious about Google dev initiatives and event in Italy?
https://developersitalia.blogspot.com

57. Thank you!
http://developers.google.com
Alfredo Morresi
plus.google.com/+AlfredoMorresi
@rainbowbreeze