The world of open source libraries and tools is vast for Android developers. Writing apps using solely Android SDK is impractical. Libraries can help you in many ways. They can speed up your development, save you creating boilerplate code and dealing with platform fragmentation, simplify your code and make it more readable and maintainable. In the talk I’m showing how several truly useful libraries can help a developer. Presented at MobCon Europe 2017.

1. Modern Android app library stack
Tomáš Kypta
#MobCon

2. Getting into Android

3. Q: “How do I get the data from the server?”

4. A: “Use AsyncTask!”
The old school approach™

5. public class MainActivity extends Activity {
@Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener {
public void onClick(View view) {
new DownloadTask().execute(inputString);
}
});
}
private class DownloadTask extends AsyncTask<String, Void, String> {
@Override protected String doInBackground(String... params) {
// download some data
}
@Override protected void onPostExecute(String result) {
TextView txt = (TextView) findViewById(R.id.text);
txt.setText(result);
}
}
}

6. Old school Android apps
• business logic in activities
• with all the bad stuff such as networking
• and memory leaks
• and crashes

7. Modern Android apps
• use cleaner architectures
• MVP, MVVM, MVI
• use libraries heavily
• use tests

8. Libraries
• save time and work
• simplify API
• back-port new APIs to older Android version

9. Ideal Android Library
• “perform one task and perform it well”
• easy to use
• open-source
• easily available
• through a remote Maven repository

10. Ideal Android Library
• doesn’t eat too much resources
• doesn’t require too many permissions
• behave nicely when crashing

11. “I wan’t my app to work on Android from version 4.1.”
98% of Android devices!

12. Support libraries
• available through Android SDK
• backport newer Android APIs
• helper classes
• debugging, testing, utilities

13. Support libraries
• AsyncTaskLoader
• com.android.support:support-core-utils:25.3.0
• ViewPager
• com.android.support:support-core-ui:25.3.0
• support fragments
• com.android.support:support-fragment:25.3.0

14. Support libraries
• AppCompatActivity, ActionBar
• com.android.support:appcompat-v7:25.3.0
• RecyclerView
• com.android.support:recyclerview-v7:25.3.0
• CardView
• com.android.support:cardview-v7:25.3.0

15. Support libraries
• com.android.support:support-annotations:25.3.0
• useful annotations
• StringRes, IntDef, Nullable, UiThread, WorkerThread, CallSuper,
VisibleForTesting, …
• com.android.support:design:25.3.0
• Material design

16. Support libraries
• Having more than 64k methods?
• And supporting Android prior 5.0?
• com.android.support:multidex:1.0.1

17. “This dependency injection thing sounds useful.”

18. Dagger 2
• dependency injection framework for Android and Java
• avoids reflection
• uses compile-time generated code

19. Dagger 2
public class SimpleGameProvider {
private ApiProvider mApiProvider;
private StorageProvider mStorageProvider;
@Inject
public SimpleProvider(ApiProvider apiProvider, StorageProvider storageProvider) {
mApiProvider = apiProvider;
mStorageProvider = storageProvider;
}
public void doSomething() {
// …
}
}

20. Dagger 2
@Module
public class AppModule {
private Context mApplicationContext;
public AppModule(Context applicationContext) {
mApplicationContext = applicationContext;
}
@Singleton @Provides
protected OtherProvider provideTheOther(Context context) {
return new OtherProvider(context);
}
}

21. Dagger 2
@Singleton
@Component(modules = {AppModule.class})
public interface AppComponent {
void inject(MainActivity activity);
}

22. Dagger 2
public class MainActivity extends AppCompatActivity {
@Inject SimpleProvider mSimpleProvider;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
((MyApplication) getApplication()).getAppComponent().inject(this);
// and now we can use mSimpleProvider
}
}

23. “My server has this REST API…”

24. Retrofit
• simple REST client for Android and Java
• annotation-based API
• type-safe
• Rx compatible

25. Retrofit
public interface GitHubApi {
@GET("/users/{username}")
User getUser(@Path("username") String username);
@GET("/users/{username}/repos")
List<Repo> getUserRepos(@Path("username") String username);
@POST("/orgs/{org}/repos")
RepoCreationResponse createRepoInOrganization(
@Path("org") String organization,
@Body RepoCreationRequest request);
}

26. Retrofit
RestAdapter adapter = new RestAdapter.Builder()
.setEndpoint(GITHUB_API_URL)
.setRequestInterceptor(new RequestInterceptor() {
@Override
public void intercept(RequestFacade request) {
request.addHeader("Accept", "application/vnd.github.v3+json");
}
})
.setLogLevel(RestAdapter.LogLevel.BASIC)
.build();
GitHubApi gitHubApi = adapter.create(GitHubApi.class);

27. “And my server has this fancy new features…”

28. OkHttp
• an efficient HTTP client for Android and Java
• requests can be easily customized
• support for HTTP/2
• connection pooling
• transparent GZIP
• response caching

29. OkHttp
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(url)
.build();
Response response = client.newCall(request).execute();
return response.body().string();

30. OkHttp
• Works out of the box with the latest Retrofit!

31. “The server returns 400. What’s wrong?”

32. Stetho
• A debug bridge
• hooks into Chrome Developer Tools

33. Stetho
• network inspection
• database inspection
• view hierarchy
• dumpapp system allowing custom plugins
• command-line interface for communication with the plugins

35. Stetho
public class MyApplication extends Application {
@Override
public void onCreate() {
super.onCreate();
Stetho.initializeWithDefaults(this);
}
}

37. Stetho
OkHttpClient okHttpClient = new OkHttpClient.Builder()
.addNetworkInterceptor(new StethoInterceptor())
.build();

38. “Why I’m getting this OutOfMemoryError?”

39. LeakCanary
• memory leak detection library
• notifies about memory leaks during app development

40. LeakCanary
dependencies {
debugCompile 'com.squareup.leakcanary:leakcanary-android:1.5'
releaseCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'
testCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'
}

41. “How to display this remote product image?”

42. Image loaders
• tons of libs
• Universal Image Loader
• Picasso
• Glide

43. Picasso
Picasso.with(context)
.load(url)
.resize(50, 50)
.centerCrop()
.placeholder(R.drawable.placeholder)
.error(R.drawable.error)
.into(vImageView);

44. “How can I notify that class?“
“There has to be some way without refactoring the whole
thing!”

45. Event bus
• for communication between decoupled parts of an app
• EventBus

46. EventBus
• events
• subscribers
• register and unregister
• post events
public static class MessageEvent { /* fields if needed */ }
@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessageEvent(MessageEvent event) {/* handle event */};
EventBus.getDefault().register(this);
EventBus.getDefault().unregister(this);
EventBus.getDefault().post(new MessageEvent());

47. “How do I get the data from the server?”
“And I have to combine couple of sources.”

48. RxJava
• general Java library
• reactive programming
• push concept
• composable data flow

49. RxJava
• useful for simple async processing
• async composition
• offers simple chaining of operations on data
• eliminates callback hell

50. RxJava
• works well with Retrofit
• can completely replace event bus libraries
• hard to learn
• RxJava 1 vs. RxJava 2
• they will coexist for some time

51. RxJava data flow
Observable
.from(new String[]{"Hello", "Droidcon!"}) creation

52. RxJava data flow
Observable
.from(new String[]{"Hello", "Droidcon!"})
.map(new Func1<String, String>() {
@Override
public String call(String s) {
return s.toUpperCase(Locale.getDefault());
}
})
creation

53. RxJava data flow
Observable
.from(new String[]{"Hello", "Droidcon!"})
.map(new Func1<String, String>() {
@Override
public String call(String s) {
return s.toUpperCase(Locale.getDefault());
}
})
.reduce(new Func2<String, String, String>() {
@Override
public String call(String s, String s2) {
return s + ' ' + s2;
}
})
creation
transformation

54. RxJava data flow
Observable
.from(new String[]{"Hello", "Droidcon!"})
.map(new Func1<String, String>() {
@Override
public String call(String s) {
return s.toUpperCase(Locale.getDefault());
}
})
.reduce(new Func2<String, String, String>() {
@Override
public String call(String s, String s2) {
return s + ' ' + s2;
}
})
.subscribe(new Action1<String>() {
@Override
public void call(String s) {
Timber.i(s);
}
});
creation
transformation
subscription

55. RxJava data flow with Java 8
creation
transformation
subscription
Observable
.from(new String[]{"Hello", "Droidcon!"})
.map(s -> s.toUpperCase(Locale.getDefault()))
.reduce((s,s2) -> s + ' ' + s2)
.subscribe(s -> Timber.i(s));

56. Other Rx libraries
RxAndroid
RxBinding
RxLifecycle
RxNavi
SQLBrite
RxRelay

57. “This new feature is great! I bet users will love it!”

58. Analytics & crash reporting
• Google Analytics
• Crashlytics
• Firebase

59. “I don’t like this Java language.”

60. Kotlin
• not a library
• a JVM programming language
• “Swift for Android devs"

61. Q: “So all I have to do is to Google for a library to do the thing?”

62. A: “think wisely before adding a new library.”

63. Final thoughts
• many potential problems
• transitive dependencies
• permissions
• app size
• slow app start
• threads
• logs

64. Questions?