TabLayout

Loklak Wok Android is a peer harvester that posts collected tweets to the Loklak Server. Along with that tweets can be searched using the app. This post describes how search API endpoint and TabLayout is used to implement the tweet searching feature. Adding Dependencies to the project This feature uses Retrofit2, Reactive extensions(RxJava2, RxAndroid and Retrofit RxJava adapter) and RetroLambda (for Java lambda support in Android). In app/build.gradle: apply plugin: 'com.android.application' apply plugin: 'me.tatarka.retrolambda' android { ... packagingOptions { exclude 'META-INF/rxjava.properties' } } dependencies { ... compile 'com.google.code.gson:gson:2.8.1' compile 'com.squareup.retrofit2:retrofit:2.3.0' compile 'com.squareup.retrofit2:converter-gson:2.3.0' compile 'com.squareup.retrofit2:adapter-rxjava2:2.3.0' compile 'io.reactivex.rxjava2:rxjava:2.0.5' compile 'io.reactivex.rxjava2:rxandroid:2.0.1' }   In build.gradle project level: dependencies { classpath 'com.android.tools.build:gradle:2.3.3' classpath 'me.tatarka:gradle-retrolambda:3.2.0' }   Implementation The search API endpoint is defined in LoklakApi interface which would provide the tweet search result. public interface LoklakApi { @GET("api/search.json") Observable<Search> getSearchedTweets( @Query("q") String query, @Query("filter") String filter, @Query("count") int count); }   The POJOs (Plain Old Java Objects) for the result of search API endpoint are obtained using jsonschema2pojo, Gson uses POJOs to convert JSON to Java objects and vice-versa. The REST client is created by Retrofit2 and is implemented in RestClient class. The Gson converter and RxJava adapter for retrofit is added in the retrofit builder. create method is called to generate the API methods(retrofit implements LoklakApi Interface). public class RestClient { private RestClient() { } private static void createRestClient() { sRetrofit = new Retrofit.Builder() .baseUrl(BASE_URL) // gson converter .addConverterFactory(GsonConverterFactory.create(gson)) // retrofit adapter for rxjava .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .build(); } private static Retrofit getRetrofitInstance() { if (sRetrofit == null) { createRestClient(); } return sRetrofit; } public static <T> T createApi(Class<T> apiInterface) { // create method to generate API methods return getRetrofitInstance().create(apiInterface); } }   As search API endpoint provides filter parameter which can be used to filter out tweets containing images and videos. So, the tweets are displayed in three categories i.e. latest, images and videos. The tweets of different category are displayed using a ViewPager. The fragments in ViewPager are inflated by a class that extends FragmentPagerAdapter. SearchFragmentPagerAdapter extends FragmentPagerAdapter, at least two methods getItem and getCount needs to be overridden. Going by the name of methods, getItem provides ith fragment to the  ViewPager and based on the value returned by getCount number of tabs are inflated in TabLayout, a ViewGroup to display fragments in ViewPager in an elegant way. For better UI, the names (here the category of tweets) are displayed, for which we override getPageTitle method. public class SearchFragmentPagerAdapter extends FragmentPagerAdapter { private List<Fragment> mFragmentList = new ArrayList<>(); private List<String> mFragmentNameList = new ArrayList<>(); public SearchFragmentPagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int position) { return mFragmentList.get(position); } @Override public int getCount() { return mFragmentList.size(); } @Override public CharSequence getPageTitle(int position) { return mFragmentNameList.get(position); } public void addFragment(Fragment fragment, String pageTitle) { mFragmentList.add(fragment); mFragmentNameList.add(pageTitle); } }   For easy understanding an analogy with RecyclerView can be made. The TabLayout here functions as a RecyclerView, ViewPager does the work of LayoutManager and FragmentPagerAdapter is analogous to RecyclerView.Adapter. Now, the fragments which contain the…