Android Networking (Without Going Crazy)

Transcript

1. Handling Android Networking (without going crazy)
2. Why do I care? • Most Android apps need to talk to a server or somewhere on the Internet • Data sync, user authentication, stream video, show ads, etc.
3. A bit about the UI thread • Android apps run in a single threaded environment • Long-running operations “block” the UI thread, causing lag / frustration / swearing • As of API 11, Android won’t allow networking operations on the UI thread
4. What should I do? • Spawn separate thread to handle any network calls • Update the UI when complete • UI elements (Views) must be updated on thread that created them (UI thread)
5. Network Threading Options • java.lang.Thread • AsyncTask • IntentService
6. Example • Download list of baseball players from a specified team, through a REST API • Display player list to the user • Assume we have Java client to talk to API
7. java.lang.Thread final int teamId = 21; new Thread(new Runnable() { @Override public void run() { ArrayList<Player> players = ApiClient. getInstance().getPlayerList( teamId); // send data to UI thread to update Message msg = new Message(); Bundle data = new Bundle(); data.putParcelableArrayList( "player_list" , players); msg.setData(data) ; mHandler.sendMessage(msg) ; } }).run();
8. java.lang.Thread • Spawn separate thread for network request • When completed send data back to UI thread to update • Remember, View objects can only be updated on UI thread
9. AsyncTask new AsyncTask<Integer , Void, List<Player>>(){ @Override protected List<Player> doInBackground (Integer... params) { int teamId = params[ 0]; return ApiClient.getInstance().getPlayerList(teamId) ; } @Override protected void onPostExecute (List<Player> players) { // this method runs on UI thread, so update list of players } }.execute(teamId) ;
10. AsyncTask • doInBackground method runs on a separate thread, passes results to onPostExecute • onPostExecute runs on UI thread, can update Views
11. AsyncTask • Looks great, right? • Try rotating your device...
13. AsyncTask Problems • Activity is destroyed and recreated on rotation, so running AsyncTask tries to update views from old Activity • AsyncTask.cancel() is broken • Best used for very short tasks (< 1s)
14. IntentService FTW! public class PlayerListService extends IntentService { public static final String ACTION_PLAYER_LIST_DOWNLOADED = "com.test.network.ACTION_PLAYER_LIST_DOWNLOADED" ; public static final String EXTRA_PLAYER_LIST = "com.test.network.EXTRA_PLAYER_LIST" ; @Override protected void onHandleIntent (Intent intent) { List<Player> players = ApiClient. getInstance().getPlayerList(teamId) ; // Send results back to UI thread Intent i = new Intent(ACTION_PLAYER_LIST_DOWNLOADED); i.putParcelableArrayListExtra( EXTRA_PLAYER_LIST, players); LocalBroadcastManager. getInstance(this).sendBroadcast(i) ; } } // Start with intent from UI thread startService(new Intent(this, PlayerListService. class));
15. IntentService • Runs on separate thread, override onHandleIntent() method • Completely separate from Activity lifecycle, shuts down when work is complete • Send data back to UI thread via Broadcast
16. Sending data to the UI Thread • Primitive data types can be sent in message data bundle or as Intent extra • Custom objects must implement Serializeable or Parcelable interfaces to be sent • http://www.parcelabler.com/ to generate code
17. Sending data to the UI Thread • Can also use ResultReceiver or an event bus to send data to UI thread • Event Bus uses publisher/subscriber model, deliver events on bus to all subscribers • Popular event buses include EventBus (greenrobot) or Otto (Square)
18. EventBus (greenrobot) // Event Class public class PlayerListEvent { private List<Player> players; public PlayerListEvent(List<Player> players) { this.players = players; } public List<Player> getPlayers() { return players; } } // Register in onCreate, onResume, onAttach, etc EventBus.getDefault().register( this); // Send Player list from IntentService EventBus.getDefault().post(new PlayerListEvent (players)); // Public method to which EventBus delivers event public void onEventMainThread (PlayerListEvent event) { mPlayers = event.getPlayers() ; // update UI... }
19. An Even Better Idea? • Retrofit turns REST API calls into a Java interface and a series of async method calls • Built on top of OkHttp (Java networking) and Okio (java.io replacement) • http://square.github.io/retrofit/
20. Retrofit • Define interface methods public interface SportsApi { @GET("/teams/{id}/players") void getPlayerList(@Path("id") int teamId, Callback<List<Player>> callback); } • Handle method callbacks SportsApiClient.getInstance().getPlayerList(teamId, new Callback<List<Player>>() { @Override public void success(List<Player> players, Response response) { // called on main thread, update UI... } @Override public void failure(RetrofitError error) { // uh oh, there was a problem... } });
21. Summary • No network calls on the UI thread! • View objects must be updated from UI thread • Android networking can be hard, but there are some great tools out there to help you
22. Questions?