Modern Android app library stack

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Modern Android app library stack Tomáš Kypta #MobCon

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Getting into Android

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

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

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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 { @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); } } }

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

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

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

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

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

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

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

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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

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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

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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

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

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“This dependency injection thing sounds useful.”

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

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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() { // … } }

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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); } }

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

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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 } }

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“My server has this REST API…”

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

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

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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);

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“And my server has this fancy new features…”

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

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

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

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

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Stetho • A debug bridge • hooks into Chrome Developer Tools

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

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

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

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“Why I’m getting this OutOfMemoryError?”

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

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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' }

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“How to display this remote product image?”

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

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

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

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

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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());

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

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

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

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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

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

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

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

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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));

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Other Rx libraries RxAndroid RxBinding RxLifecycle RxNavi SQLBrite RxRelay

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

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Analytics & crash reporting • Google Analytics • Crashlytics • Firebase

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“I don’t like this Java language.”

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

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

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

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

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Questions?