A presentation about how to make your Android application work better in different offline scenarios. First presented at DroidCon London 2015.

1. Staying alive
Online and offline
Erik Hellman, BonTouch
@ErikHellman

2. How well does your app
work offline?

3. When leaving my apartment

6. Why?
4 Reduce glitches
4 Roaming users
4 Missing coverage
4 Improve performance
4 Reduce data costs

7. Offline examples

12. How?
4 Connectivity detection
4 Request queing
4 Caching
4 Preloading

13. Challenges
4 Captive Portals
4 Network handover
4 Temporary network loss
4 Timeouts
4 2G Voice and Data
4 Local Storage
4 Request Serialization
4 ...and more

14. Detecting connectivity
boolean isNetworkAvailable() {
ConnectivityManager mgr = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = mgr.getActiveNetworkInfo();
return networkInfo != null && networkInfo.isConnected();
}
4 Checks network state right now
4 Captive portals detection (since API level 17)
4 Poor networks (since API level 16)
4 Must be called before every network operation
4 Will indicate DISCONNECTED if background data is disabled!

15. Listen for changes
private void setupNetworkChangeListener() {
IntentFilter intentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
this.networkStateReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
ConnectivityManager mgr = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = mgr.getActiveNetworkInfo();
notifyNetworkState(networkInfo != null && networkInfo.isConnected());
}
};
registerReceiver(networkStateReceiver, intentFilter);
}
4 Continously listen for network state changes
4 Remember to unregister!

16. NetworkInfo.State
public enum State {
CONNECTING,
CONNECTED,
SUSPENDED,
DISCONNECTING,
DISCONNECTED,
UNKNOWN
}

17. NetworkInfo.DetailedState
public enum DetailedState {
IDLE,
SCANNING,
CONNECTING,
AUTHENTICATING,
OBTAINING_IPADDR,
CONNECTED,
SUSPENDED,
DISCONNECTING,
DISCONNECTED,
FAILED,
BLOCKED,
VERIFYING_POOR_LINK,
CAPTIVE_PORTAL_CHECK
}

18. private static final EnumMap<DetailedState, State> stateMap =
new EnumMap<DetailedState, State>(DetailedState.class);
static {
stateMap.put(DetailedState.IDLE, State.DISCONNECTED);
stateMap.put(DetailedState.SCANNING, State.DISCONNECTED);
stateMap.put(DetailedState.CONNECTING, State.CONNECTING);
stateMap.put(DetailedState.AUTHENTICATING, State.CONNECTING);
stateMap.put(DetailedState.OBTAINING_IPADDR, State.CONNECTING);
stateMap.put(DetailedState.VERIFYING_POOR_LINK, State.CONNECTING);
stateMap.put(DetailedState.CAPTIVE_PORTAL_CHECK, State.CONNECTING);
stateMap.put(DetailedState.CONNECTED, State.CONNECTED);
stateMap.put(DetailedState.SUSPENDED, State.SUSPENDED);
stateMap.put(DetailedState.DISCONNECTING, State.DISCONNECTING);
stateMap.put(DetailedState.DISCONNECTED, State.DISCONNECTED);
stateMap.put(DetailedState.FAILED, State.DISCONNECTED);
stateMap.put(DetailedState.BLOCKED, State.DISCONNECTED);
}

19. Unexpected conditions
4 2G Voice and Data
4 Flight Mode
public static boolean isAirplaneModeOn(Context context) {
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
return Settings.System.getInt(context.getContentResolver(),
Settings.System.AIRPLANE_MODE_ON, 0) != 0;
} else {
return Settings.Global.getInt(context.getContentResolver(),
Settings.Global.AIRPLANE_MODE_ON, 0) != 0;
}
}

23. 15 minutes
socket timeout

24. Response Times:
The 3 Important Limits
4 0.1 seconds - system is reacting instantaneously
4 1.0 seconds - limit for user's flow of thought to stay uninterrupted
4 10 seconds - limit for keeping the user's attention
...response time guidelines for web-based applications are the same as for all
other applications...
— Jakob Nielsen, http://www.nngroup.com/articles/response-times-3-
important-limits/

25. Timeout for HttpURLConnection
URL url = new URL(url);
HttpURLConnection urlConnection = url.openConnection();
urlConnection.setConnectTimeout(CONNECTION_TIMEOUT);
urlConnection.setReadTimeout(CONNECTION_TIMEOUT);

26. Timeout for OkHttpClient
OkHttpClient client = new OkHttpClient();
client.setConnectTimeout(CONNECTION_TIMEOUT);
client.setReadTimeout(CONNECTION_TIMEOUT);

27. Request Serialzation

30. Queing outgoing requests
// In your Activity
startService(buildRequestIntent(url, data));
// IntentService.onHandleIntent()
is(isConnected(this)) {
performRequest(url, data);
} else {
serializeRequest(url, data);
}
// BroadcastReceiver listening for network changes
if(isConnected(context)) {
context.startService(new Intent(ACTION_SEND_QUEUED_REQUESTS));
}

31. Alternatives
4 Firebase
4 Couchebase

32. Request serialization
4 Query params?
4 Request body?
4 HTTP headers?
4 Timestamp?

33. Request serialization
public void serializeRequest(url, data) {
ContentValues values = new ContentValues();
values.put("url", url);
values.put("data", data);
getContentResolver.insert(...);
}

34. Caching
4 Not HTTP Response cache!
4 Custom cache implementations
4 Don't evict when offline?
4 Context.getCacheDir(), Context.getFilesDir() or
Context.getExternalFilesDir()?

35. Caching examples

40. DiskLruCache.java

41. Load from cache or network?
// Our sources (left as an exercise for the reader)
Observable<Data> memory = ...;
Observable<Data> disk = ...;
Observable<Data> network = ...;
// Retrieve the first source with data
Observable<Data> source = Observable
.concat(memory, disk, network)
.first();
4 Dan Lew, http://blog.danlew.net/2015/06/22/loading-data-from-
multiple-sources-with-rxjava/

42. Preload data for offline
4 Assets or Raw resources (100 MB)
4 APK Expansion files (2 * 2GB)
4 Download at first startup (unlimited)

43. How much data?
Street addresses
4 Sweden: 650 000 ~ 7 MB
4 US: 154 million ~ 1.6 GB

44. Preloading SQLite DB
private SQLiteDatabase openPreloadedSQLiteDB() {
File localCopy = new File(getFilesDir(), DB_NAME);
if (localCopy.exists()) { // TODO Perform version check!
InputStream inputStream = getResources().openRawResource(R.raw.preloaded_db);
readStreamToFile(inputStream, localCopy);
}
return SQLiteDatabase.openOrCreateDatabase(localCopy, null);
}

45. Local storage
4 Micromax Canvas A1 (Android One) - 2GB internal
storage
4 Use external storage
public static void saveFileToExternalStorage(Context context, String filename, byte[] data) {
File appPrivateFile = new File(context.getExternalFilesDir(null), filename);
writeBytesToFile(data, appPrivateFile);
}

46. Mesh networking?
4 Bluetooth
4 WiFi Direct

47. Conclusions
Don't ignore offline!

48. Thanks for listening!
@ErikHellman