[Roma Mazur] Android Loader, problems and solutions

Presentation from GDG DevFest - the biggest Google related event in Ukraine. October 24-25, Lviv. Learn more at http://devfest.gdg.org.ua/

Transcript

1. Android Loader
 Problems and solutions #androidDev #loader Roman Mazur Software Engineer, Stanfy
2. #dfua Lovely Triangle LoaderCallbacks LoaderManager Loader create manage, notify manage notify
3. #dfua getLoaderManager().initLoader(MAGIC_ID, null, new LoaderManager.LoaderCallbacks<Cursor>() { // TODO }); int that identifies your operation
4. #dfua getLoaderManager().initLoader(MAGIC_ID, null, new LoaderManager.LoaderCallbacks<Cursor>() { @Override public Loader<Cursor> onCreateLoader(int id, Bundle args) { CursorLoader loader = new CursorLoader(getApplicationContext()); loader.setUri(SOME_URI); return loader; } // TODO }); create a Loader that performs your operation
5. #dfua getLoaderManager().initLoader(MAGIC_ID, null, new LoaderManager.LoaderCallbacks<Cursor>() { @Override public Loader<Cursor> onCreateLoader(int id, Bundle args) { CursorLoader loader = new CursorLoader(getApplicationContext()); loader.setUri(SOME_URI); return loader; } @Override public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) { // cursor loaded } // TODO }); implement an action to be 
 taken when data is loaded
6. #dfua getLoaderManager().initLoader(MAGIC_ID, null, new LoaderManager.LoaderCallbacks<Cursor>() { @Override public Loader<Cursor> onCreateLoader(int id, Bundle args) { CursorLoader loader = new CursorLoader(getApplicationContext()); loader.setUri(SOME_URI); return loader; } @Override public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) { // cursor loaded } @Override public void onLoaderReset(Loader<Cursor> loader) { // does anybody know what to do here? } }); get rid of any references 
 to the data previously loaded
7. #dfua @Override protected void onCreate(Bundle savedState) { super.onCreate(savedState); getLoaderManager().initLoader(MAGIC_ID, null, new LoaderManager.LoaderCallbacks<Cursor>() { @Override public Loader<Cursor> onCreateLoader(int id, Bundle args) { CursorLoader loader = new CursorLoader(getApplicationContext()); loader.setUri(SOME_URI); return loader; } @Override public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) { // cursor loaded } @Override public void onLoaderReset(Loader<Cursor> loader) { // get rid of data } }); } the simplest case:
 init in 
 Activity.onCreate, Fragment.onCreate, Fragment.onActivityCreated
8. #dfua public class Loader<D> { public void deliverResult(D data) { } protected void onStartLoading() { } protected boolean onCancelLoad() { } protected void onForceLoad() { } protected void onStopLoading() { } protected void onAbandon() { } protected void onReset() { } } What you have to think about implementing a custom loader
9. #dfua @Override protected void onCreate(Bundle savedState) { super.onCreate(savedState); findViewById(android.R.id.button1).setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { getLoaderManager().initLoader(MAGIC_ID, null, callback); } }); } start loading when button is tapped
10. #dfua @Override protected void onCreate(Bundle savedState) { super.onCreate(savedState); if (isLoadingInProgress(savedState)) { getLoaderManager().initLoader(MAGIC_ID, null, callback); } findViewById(android.R.id.button1).setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { loading = true; getLoaderManager().initLoader(MAGIC_ID, null, callback); } }); } 1 save your state;
 don’t forget about 
 onSaveInstanceState 2 attach a callback
 if bundle has your
 flag set
11. #dfua @Override protected void onCreate(Bundle savedState) { super.onCreate(savedState); if (isLoadingInProgress(savedState)) { getLoaderManager().initLoader(MAGIC_ID, null, callback); } findViewById(android.R.id.button1).setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { loading = true; getLoaderManager().restartLoader(MAGIC_ID, null, callback); } }); } e.g. if you want to submit an order ensures your operation will be performed
12. #dfua More Critics by Mark Murphy http://commonsware.com/blog/2014/03/31/cwac-loaderex-failed-abstractions.html • Need to work around LoaderManager optimisations • Poor flexibility
13. #dfua More Critics Need to work around LoaderManager optimisations • Poor flexibility • Errors handling ?
14. #dfua public class Loader<D> { public void deliverResult(D data) { } protected void onStartLoading() { } protected boolean onCancelLoad() { } protected void onForceLoad() { } protected void onStopLoading() { } protected void onAbandon() { } protected void onReset() { } } Loader abstraction Serves for solving one main problem:
 control your async operation execution. Control is done by LoaderManager through
 binding to UI lifecycle. Delivered data is retained.
15. Loader is not that bad
16. Enroscar Async simplifies Loader usage 
 https://github.com/stanfy/enroscar/tree/master/async
17. #dfua Define Operations class TwitterOperations { final TwitterApi api; @Load Async<List<Tweet>> loadTweets(String query) { return Tools.async(new Callable<List<Tweet>>() { @Override public List<Tweet> call() { return api.search(query); } }); } } @Send Async<Boolean> postTweet(String message) { return Tools.async(new Callable<Boolean>() { @Override public Boolean call() { return api.post(message); } }); }
18. #dfua Use Generated Operator // somewhere in your Activity TwitterOperationsOperator operator = TwitterOperationsOperator.build() .operations(new TwitterOperations(api)) .loaderManager(getSupportLoaderManager()) .context(this) .get(); // trigger operator.loadTweets(“#dfua”); operator.postTweet(“@roman_mazur talks about Enroscar Async”);
19. #dfua Subscribe to Operation Results operator .when().loadTweetsIsFinished() .doOnResult(action) .doOnError(errorAction) .alsoWhen().postTweetIsFinished() .doOnResult(anotherAction) .doOnError(anotherErrorAction);
20. #dfua Reactive Extensions class TwitterOperations { @Load Observable<List<Tweet>> loadTweets(String query) { } @Load Observable<Boolean> postTweet(String message) { } }
21. #dfua Reactive Extensions operator .when().loadTweetsIsFinished() .subscribe(action); operator. .when().postTweetIsFinished() .map(res -> res ? “Your tweet is posted!” : “Too big message!”) .subscribe(displayUserMessage);
22. #dfua LoaderCallbacks LoaderManager Loader create manage, notify manage notify
23. #dfua Subscription Operator Operations Object manage, notify manage notify
24. Avoid IDs management Enroscar Async lets you
25. Write fluent subscriptions Enroscar Async lets you
26. Simplify errors handling Enroscar Async lets you
27. Put rx.Observable behind Loader Enroscar Async lets you
28. Thank you @roman_mazur google.com/+RomanMazur github.com/stanfy twitter g+ github