#3822 Convert SubCategoryImagesListFragment to use Pagination (#3824)

app/src/main/java/fr/free/nrw/commons/bookmarks/BookmarksActivity.java

@@ -141,5 +141,7 @@ public class BookmarksActivity extends NavigationBaseActivity
     }
 
     @Override
-    public void requestMoreImages() { }
+    public void onMediaClicked(int position) {
+        //TODO use with pagination
+    }
 }

app/src/main/java/fr/free/nrw/commons/category/CategoriesModel.kt

@@ -93,6 +93,7 @@ class CategoriesModel @Inject constructor(
         else
             categoryClient.searchCategoriesForPrefix(term.toLowerCase(), SEARCH_CATS_LIMIT)
                 .map { it.sortedWith(StringSortingUtils.sortBySimilarity(term)) }
+                .toObservable()
     }
 
     private fun categoriesFromDepiction(selectedDepictions: List<DepictedItem>) =
@@ -126,7 +127,7 @@ class CategoriesModel @Inject constructor(
      * @return
      */
     private fun getTitleCategories(title: String): Observable<List<String>> {
-        return categoryClient.searchCategories(title.toLowerCase(), SEARCH_CATS_LIMIT)
+        return categoryClient.searchCategories(title.toLowerCase(), SEARCH_CATS_LIMIT).toObservable()
     }
 
 

app/src/main/java/fr/free/nrw/commons/category/CategoryClient.kt

@@ -1,16 +1,21 @@
 package fr.free.nrw.commons.category
 
-import io.reactivex.Observable
+import io.reactivex.Single
 import org.wikipedia.dataclient.mwapi.MwQueryResponse
 import javax.inject.Inject
 import javax.inject.Singleton
 
 const val CATEGORY_PREFIX = "Category:"
+const val SUB_CATEGORY_CONTINUATION_PREFIX = "sub_category_"
+const val PARENT_CATEGORY_CONTINUATION_PREFIX = "parent_category_"
+
 /**
  * Category Client to handle custom calls to Commons MediaWiki APIs
  */
 @Singleton
-class CategoryClient @Inject constructor(private val categoryInterface: CategoryInterface) {
+class CategoryClient @Inject constructor(private val categoryInterface: CategoryInterface) :
+    ContinuationClient<MwQueryResponse, String>() {
+
     /**
      * Searches for categories containing the specified string.
      *
@@ -21,8 +26,8 @@ class CategoryClient @Inject constructor(private val categoryInterface: Category
      */
     @JvmOverloads
     fun searchCategories(filter: String?, itemLimit: Int, offset: Int = 0):
-            Observable<List<String>> {
+            Single<List<String>> {
-        return responseToCategoryName(categoryInterface.searchCategories(filter, itemLimit, offset))
+        return responseMapper(categoryInterface.searchCategories(filter, itemLimit, offset))
     }
 
     /**
@@ -35,8 +40,8 @@ class CategoryClient @Inject constructor(private val categoryInterface: Category
      */
     @JvmOverloads
     fun searchCategoriesForPrefix(prefix: String?, itemLimit: Int, offset: Int = 0):
-            Observable<List<String>> {
+            Single<List<String>> {
-        return responseToCategoryName(
+        return responseMapper(
             categoryInterface.searchCategoriesForPrefix(prefix, itemLimit, offset)
         )
     }
@@ -48,8 +53,12 @@ class CategoryClient @Inject constructor(private val categoryInterface: Category
      * @param categoryName Category name as defined on commons
      * @return Observable emitting the categories returned. If our search yielded "Category:Test", "Test" is emitted.
      */
-    fun getSubCategoryList(categoryName: String?): Observable<List<String>> {
+    fun getSubCategoryList(categoryName: String): Single<List<String>> {
-        return responseToCategoryName(categoryInterface.getSubCategoryList(categoryName))
+        return continuationRequest(SUB_CATEGORY_CONTINUATION_PREFIX, categoryName) {
+            categoryInterface.getSubCategoryList(
+                categoryName, it
+            )
+        }
     }
 
     /**
@@ -59,19 +68,29 @@ class CategoryClient @Inject constructor(private val categoryInterface: Category
      * @param categoryName Category name as defined on commons
      * @return
      */
-    fun getParentCategoryList(categoryName: String?): Observable<List<String>> {
+    fun getParentCategoryList(categoryName: String): Single<List<String>> {
-        return responseToCategoryName(categoryInterface.getParentCategoryList(categoryName))
+        return continuationRequest(PARENT_CATEGORY_CONTINUATION_PREFIX, categoryName) {
+            categoryInterface.getParentCategoryList(categoryName, it)
+        }
     }
 
-    /**
+    fun resetSubCategoryContinuation(category: String) {
-     * Internal function to reduce code reuse. Extracts the categories returned from MwQueryResponse.
+        resetContinuation(SUB_CATEGORY_CONTINUATION_PREFIX, category)
-     *
+    }
-     * @param responseObservable The query response observable
+
-     * @return Observable emitting the categories returned. If our search yielded "Category:Test", "Test" is emitted.
+    fun resetParentCategoryContinuation(category: String) {
-     */
+        resetContinuation(PARENT_CATEGORY_CONTINUATION_PREFIX, category)
-    private fun responseToCategoryName(responseObservable: Observable<MwQueryResponse>): Observable<List<String>> {
+    }
-        return responseObservable
+
-            .map { it.query()?.pages() ?: emptyList() }
+    override fun responseMapper(
+        networkResult: Single<MwQueryResponse>,
+        key: String?
+    ): Single<List<String>> {
+        return networkResult
+            .map {
+                handleContinuationResponse(it.continuation(), key)
+                it.query()?.pages() ?: emptyList()
+            }
             .map {
                 it.map { page -> page.title().replace(CATEGORY_PREFIX, "") }
             }

app/src/main/java/fr/free/nrw/commons/category/CategoryDetailsActivity.java

@@ -20,6 +20,8 @@ import fr.free.nrw.commons.R;
 import fr.free.nrw.commons.Utils;
 import fr.free.nrw.commons.explore.ViewPagerAdapter;
 import fr.free.nrw.commons.explore.categories.media.CategoriesMediaFragment;
+import fr.free.nrw.commons.explore.categories.parent.ParentCategoriesFragment;
+import fr.free.nrw.commons.explore.categories.sub.SubCategoriesFragment;
 import fr.free.nrw.commons.media.MediaDetailPagerFragment;
 import fr.free.nrw.commons.theme.NavigationBaseActivity;
 import java.util.ArrayList;
@@ -69,25 +71,21 @@ public class CategoryDetailsActivity extends NavigationBaseActivity
         List<Fragment> fragmentList = new ArrayList<>();
         List<String> titleList = new ArrayList<>();
         categoriesMediaFragment = new CategoriesMediaFragment();
-        SubCategoryListFragment subCategoryListFragment = new SubCategoryListFragment();
+        SubCategoriesFragment subCategoryListFragment = new SubCategoriesFragment();
-        SubCategoryListFragment parentCategoryListFragment = new SubCategoryListFragment();
+        ParentCategoriesFragment parentCategoriesFragment = new ParentCategoriesFragment();
         categoryName = getIntent().getStringExtra("categoryName");
         if (getIntent() != null && categoryName != null) {
             Bundle arguments = new Bundle();
             arguments.putString("categoryName", categoryName);
-            arguments.putBoolean("isParentCategory", false);
             categoriesMediaFragment.setArguments(arguments);
             subCategoryListFragment.setArguments(arguments);
-            Bundle parentCategoryArguments = new Bundle();
+            parentCategoriesFragment.setArguments(arguments);
-            parentCategoryArguments.putString("categoryName", categoryName);
-            parentCategoryArguments.putBoolean("isParentCategory", true);
-            parentCategoryListFragment.setArguments(parentCategoryArguments);
         }
         fragmentList.add(categoriesMediaFragment);
         titleList.add("MEDIA");
         fragmentList.add(subCategoryListFragment);
         titleList.add("SUBCATEGORIES");
-        fragmentList.add(parentCategoryListFragment);
+        fragmentList.add(parentCategoriesFragment);
         titleList.add("PARENT CATEGORIES");
         viewPagerAdapter.setTabData(fragmentList, titleList);
         viewPagerAdapter.notifyDataSetChanged();
@@ -133,7 +131,6 @@ public class CategoryDetailsActivity extends NavigationBaseActivity
      */
     public static void startYourself(Context context, String categoryName) {
         Intent intent = new Intent(context, CategoryDetailsActivity.class);
-        intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT | Intent.FLAG_ACTIVITY_SINGLE_TOP);
         intent.putExtra("categoryName", categoryName);
         context.startActivity(intent);
     }
@@ -212,12 +209,4 @@ public class CategoryDetailsActivity extends NavigationBaseActivity
         }
     }
 
-    /**
-     * This method is called when viewPager has reached its end.
-     * Fetches more images using search query and adds it to the grid view and viewpager adapter
-     */
-    @Override
-    public void requestMoreImages() {
-        //unneeded
-    }
 }

app/src/main/java/fr/free/nrw/commons/category/CategoryImagesActivity.java

@@ -187,12 +187,8 @@ public class CategoryImagesActivity
         }
     }
 
-    /**
-     * This method is called when viewPager has reached its end.
-     * Fetches more images using search query and adds it to the gridView and viewpager adapter
-     */
     @Override
-    public void requestMoreImages() {
+    public void onMediaClicked(int position) {
-        //unneeded
+        // this class is unused and will be deleted
     }
 }

app/src/main/java/fr/free/nrw/commons/category/CategoryImagesCallback.java

@@ -7,7 +7,7 @@ package fr.free.nrw.commons.category;
 
 public interface CategoryImagesCallback {
    void viewPagerNotifyDataSetChanged();
-   void requestMoreImages();
+   void onMediaClicked(int position);
 }
 
 

app/src/main/java/fr/free/nrw/commons/category/CategoryInterface.java

@@ -1,10 +1,11 @@
 package fr.free.nrw.commons.category;
 
+import io.reactivex.Single;
+import java.util.Map;
 import org.wikipedia.dataclient.mwapi.MwQueryResponse;
-
-import io.reactivex.Observable;
 import retrofit2.http.GET;
 import retrofit2.http.Query;
+import retrofit2.http.QueryMap;
 
 /**
  * Interface for interacting with Commons category related APIs
@@ -20,7 +21,7 @@ public interface CategoryInterface {
      */
     @GET("w/api.php?action=query&format=json&formatversion=2"
             + "&generator=search&gsrnamespace=14")
-    Observable<MwQueryResponse> searchCategories(@Query("gsrsearch") String filter,
+    Single<MwQueryResponse> searchCategories(@Query("gsrsearch") String filter,
                                                  @Query("gsrlimit") int itemLimit, @Query("gsroffset") int offset);
 
     /**
@@ -32,16 +33,18 @@ public interface CategoryInterface {
      */
     @GET("w/api.php?action=query&format=json&formatversion=2"
             + "&generator=allcategories")
-    Observable<MwQueryResponse> searchCategoriesForPrefix(@Query("gacprefix") String prefix,
+    Single<MwQueryResponse> searchCategoriesForPrefix(@Query("gacprefix") String prefix,
                                                           @Query("gaclimit") int itemLimit, @Query("gacoffset") int offset);
 
     @GET("w/api.php?action=query&format=json&formatversion=2"
             + "&generator=categorymembers&gcmtype=subcat"
-            + "&prop=info&gcmlimit=500")
+            + "&prop=info&gcmlimit=50")
-    Observable<MwQueryResponse> getSubCategoryList(@Query("gcmtitle") String categoryName);
+    Single<MwQueryResponse> getSubCategoryList(@Query("gcmtitle") String categoryName,
+        @QueryMap(encoded = true) Map<String, String> continuation);
 
     @GET("w/api.php?action=query&format=json&formatversion=2"
-            + "&generator=categories&prop=info&gcllimit=500")
+            + "&generator=categories&prop=info&gcllimit=50")
-    Observable<MwQueryResponse> getParentCategoryList(@Query("titles") String categoryName);
+    Single<MwQueryResponse> getParentCategoryList(@Query("titles") String categoryName,
+        @QueryMap(encoded = true) Map<String, String> continuation);
 
 }

app/src/main/java/fr/free/nrw/commons/category/ContinuationClient.kt

@@ -0,0 +1,41 @@
+package fr.free.nrw.commons.category
+
+import io.reactivex.Single
+
+
+abstract class ContinuationClient<Network, Domain> {
+    private val continuationStore: MutableMap<String, Map<String, String>?> = mutableMapOf()
+    private val continuationExists: MutableMap<String, Boolean> = mutableMapOf()
+
+    private fun hasMorePagesFor(key: String) = continuationExists[key] ?: true
+    fun continuationRequest(
+        prefix: String,
+        name: String,
+        requestFunction: (Map<String, String>) -> Single<Network>
+    ): Single<List<Domain>> {
+        val key = "$prefix$name"
+        return if (hasMorePagesFor(key)) {
+            responseMapper(requestFunction(continuationStore[key] ?: emptyMap()), key)
+        } else {
+            Single.just(emptyList())
+        }
+    }
+
+    abstract fun responseMapper(networkResult: Single<Network>, key: String?=null): Single<List<Domain>>
+
+    fun handleContinuationResponse(continuation:Map<String,String>?, key:String?){
+        if (key != null) {
+            continuationExists[key] =
+                continuation?.let { continuation ->
+                    continuationStore[key] = continuation
+                    true
+                } ?: false
+        }
+    }
+
+    protected fun resetContinuation(prefix: String, category: String) {
+        continuationExists.remove("$prefix$category")
+        continuationStore.remove("$prefix$category")
+    }
+
+}

app/src/main/java/fr/free/nrw/commons/category/SubCategoryListFragment.java

@@ -1,154 +0,0 @@
-package fr.free.nrw.commons.category;
-
-
-import static android.view.View.GONE;
-import static android.view.View.VISIBLE;
-import static fr.free.nrw.commons.category.CategoryClientKt.CATEGORY_PREFIX;
-
-import android.content.Intent;
-import android.content.res.Configuration;
-import android.os.Bundle;
-import android.view.LayoutInflater;
-import android.view.View;
-import android.view.ViewGroup;
-import android.widget.ProgressBar;
-import android.widget.TextView;
-import androidx.recyclerview.widget.GridLayoutManager;
-import androidx.recyclerview.widget.LinearLayoutManager;
-import androidx.recyclerview.widget.RecyclerView;
-import butterknife.BindView;
-import butterknife.ButterKnife;
-import fr.free.nrw.commons.R;
-import fr.free.nrw.commons.di.CommonsDaggerSupportFragment;
-import fr.free.nrw.commons.explore.categories.search.SearchCategoriesAdapter;
-import fr.free.nrw.commons.utils.NetworkUtils;
-import fr.free.nrw.commons.utils.ViewUtil;
-import io.reactivex.android.schedulers.AndroidSchedulers;
-import io.reactivex.schedulers.Schedulers;
-import java.util.List;
-import javax.inject.Inject;
-import kotlin.Unit;
-import timber.log.Timber;
-
-/**
- * Displays the category search screen.
- */
-
-public class SubCategoryListFragment extends CommonsDaggerSupportFragment {
-
-    @BindView(R.id.imagesListBox)
-    RecyclerView categoriesRecyclerView;
-    @BindView(R.id.imageSearchInProgress)
-    ProgressBar progressBar;
-    @BindView(R.id.imagesNotFound)
-    TextView categoriesNotFoundView;
-
-    private String categoryName = null;
-    @Inject CategoryClient categoryClient;
-
-    private SearchCategoriesAdapter categoriesAdapter;
-    private boolean isParentCategory = true;
-
-
-    @Override
-    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
-        View rootView = inflater.inflate(R.layout.fragment_browse_image, container, false);
-        ButterKnife.bind(this, rootView);
-        categoryName = getArguments().getString("categoryName");
-        isParentCategory = getArguments().getBoolean("isParentCategory");
-        initSubCategoryList();
-        if (getActivity().getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT){
-            categoriesRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
-        }
-        else{
-            categoriesRecyclerView.setLayoutManager(new GridLayoutManager(getContext(), 2));
-        }
-        categoriesAdapter = new SearchCategoriesAdapter(item->{
-            Intent intent = new Intent(getContext(), CategoryDetailsActivity.class);
-            intent.putExtra("categoryName", item);
-            getContext().startActivity(intent);
-            return Unit.INSTANCE;
-        });
-        categoriesRecyclerView.setAdapter(categoriesAdapter);
-        return rootView;
-    }
-
-    /**
-     * Checks for internet connection and then initializes the recycler view with all(max 500) categories of the searched query
-     * Clearing categoryAdapter every time new keyword is searched so that user can see only new results
-     */
-    public void initSubCategoryList() {
-        categoriesNotFoundView.setVisibility(GONE);
-        if (!NetworkUtils.isInternetConnectionEstablished(getContext())) {
-            handleNoInternet();
-            return;
-        }
-        progressBar.setVisibility(View.VISIBLE);
-        if (isParentCategory) {
-            compositeDisposable.add(categoryClient.getParentCategoryList(
-                CATEGORY_PREFIX +categoryName)
-                    .subscribeOn(Schedulers.io())
-                    .observeOn(AndroidSchedulers.mainThread())
-                    .subscribe(this::handleSuccess, this::handleError));
-        } else {
-            compositeDisposable.add(categoryClient.getSubCategoryList(
-                CATEGORY_PREFIX +categoryName)
-                    .subscribeOn(Schedulers.io())
-                    .observeOn(AndroidSchedulers.mainThread())
-                    .subscribe(this::handleSuccess, this::handleError));
-        }
-    }
-
-
-    /**
-     * Handles the success scenario
-     * it initializes the recycler view by adding items to the adapter
-     * @param subCategoryList
-     */
-    private void handleSuccess(List<String> subCategoryList) {
-        if (subCategoryList == null || subCategoryList.isEmpty()) {
-            initEmptyView();
-        }
-        else {
-            progressBar.setVisibility(View.GONE);
-            categoriesAdapter.addAll(subCategoryList);
-            categoriesAdapter.notifyDataSetChanged();
-        }
-    }
-
-    /**
-     * Logs and handles API error scenario
-     * @param throwable
-     */
-    private void handleError(Throwable throwable) {
-        if (!isParentCategory){
-            Timber.e(throwable, "Error occurred while loading queried subcategories");
-            ViewUtil.showShortSnackbar(categoriesRecyclerView,R.string.error_loading_categories);
-        }else {
-            Timber.e(throwable, "Error occurred while loading queried parentcategories");
-            ViewUtil.showShortSnackbar(categoriesRecyclerView,R.string.error_loading_categories);
-        }
-    }
-
-    /**
-     * Handles the UI updates for a empty results scenario
-     */
-    private void initEmptyView() {
-        progressBar.setVisibility(GONE);
-        categoriesNotFoundView.setVisibility(VISIBLE);
-        if (!isParentCategory){
-            categoriesNotFoundView.setText(getString(R.string.no_subcategory_found));
-        }else {
-            categoriesNotFoundView.setText(getString(R.string.no_parentcategory_found));
-        }
-
-    }
-
-    /**
-     * Handles the UI updates for no internet scenario
-     */
-    private void handleNoInternet() {
-        progressBar.setVisibility(GONE);
-        ViewUtil.showShortSnackbar(categoriesRecyclerView, R.string.no_internet);
-    }
-}

app/src/main/java/fr/free/nrw/commons/contributions/ContributionBoundaryCallback.kt

@@ -51,9 +51,6 @@ class ContributionBoundaryCallback @Inject constructor(
      * Fetches contributions using the MediaWiki API
      */
     fun fetchContributions() {
-        if (mediaClient.doesMediaListForUserHaveMorePages(sessionManager.userName!!).not()) {
-            return
-        }
         compositeDisposable.add(
             mediaClient.getMediaListForUser(sessionManager.userName!!)
                 .map { mediaList: List<Media?> ->

app/src/main/java/fr/free/nrw/commons/di/FragmentBuilderModule.java

@@ -4,14 +4,15 @@ import dagger.Module;
 import dagger.android.ContributesAndroidInjector;
 import fr.free.nrw.commons.bookmarks.locations.BookmarkLocationsFragment;
 import fr.free.nrw.commons.bookmarks.pictures.BookmarkPicturesFragment;
-import fr.free.nrw.commons.category.SubCategoryListFragment;
 import fr.free.nrw.commons.contributions.ContributionsFragment;
 import fr.free.nrw.commons.contributions.ContributionsListFragment;
 import fr.free.nrw.commons.explore.categories.media.CategoriesMediaFragment;
+import fr.free.nrw.commons.explore.categories.parent.ParentCategoriesFragment;
+import fr.free.nrw.commons.explore.categories.search.SearchCategoryFragment;
+import fr.free.nrw.commons.explore.categories.sub.SubCategoriesFragment;
 import fr.free.nrw.commons.explore.depictions.child.ChildDepictionsFragment;
 import fr.free.nrw.commons.explore.depictions.media.DepictedImagesFragment;
 import fr.free.nrw.commons.explore.depictions.parent.ParentDepictionsFragment;
-import fr.free.nrw.commons.explore.categories.search.SearchCategoryFragment;
 import fr.free.nrw.commons.explore.depictions.search.SearchDepictionsFragment;
 import fr.free.nrw.commons.explore.media.SearchMediaFragment;
 import fr.free.nrw.commons.explore.recentsearches.RecentSearchesFragment;
@@ -49,9 +50,6 @@ public abstract class FragmentBuilderModule {
     @ContributesAndroidInjector
     abstract DepictedImagesFragment bindDepictedImagesFragment();
 
-    @ContributesAndroidInjector
-    abstract SubCategoryListFragment bindSubCategoryListFragment();
-
     @ContributesAndroidInjector
     abstract SearchMediaFragment bindBrowseImagesListFragment();
 
@@ -99,4 +97,10 @@ public abstract class FragmentBuilderModule {
 
     @ContributesAndroidInjector
     abstract CategoriesMediaFragment bindCategoriesMediaFragment();
+
+    @ContributesAndroidInjector
+    abstract SubCategoriesFragment bindSubCategoriesFragment();
+
+    @ContributesAndroidInjector
+    abstract ParentCategoriesFragment bindParentCategoriesFragment();
 }

app/src/main/java/fr/free/nrw/commons/explore/ExploreActivity.java

@@ -7,7 +7,6 @@ import android.view.Menu;
 import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.View;
-import android.widget.AdapterView;
 import android.widget.FrameLayout;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
@@ -31,8 +30,7 @@ import java.util.List;
 
 public class ExploreActivity
         extends NavigationBaseActivity
-        implements MediaDetailPagerFragment.MediaDetailProvider,
+        implements MediaDetailPagerFragment.MediaDetailProvider, CategoryImagesCallback {
-        AdapterView.OnItemClickListener, CategoryImagesCallback {
 
     private static final String FEATURED_IMAGES_CATEGORY = "Featured_pictures_on_Wikimedia_Commons";
     private static final String MOBILE_UPLOADS_CATEGORY = "Uploaded_with_Mobile/Android";
@@ -163,21 +161,11 @@ public class ExploreActivity
         super.onBackPressed();
     }
 
-
-    /**
-     * This method is called when viewPager has reached its end.
-     * Fetches more images and adds them to the recycler view and viewpager adapter
-     */
-    @Override
-    public void requestMoreImages() {
-        //unneeded
-    }
-
     /**
      * This method is called onClick of media inside category featured images or mobile uploads.
      */
     @Override
-    public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
+    public void onMediaClicked( int position) {
         tabLayout.setVisibility(View.GONE);
         viewPager.setVisibility(View.GONE);
         mediaContainer.setVisibility(View.VISIBLE);
@@ -195,7 +183,7 @@ public class ExploreActivity
             // coming back to the explore activity. See https://github.com/commons-app/apps-android-commons/issues/1631
             // https://stackoverflow.com/questions/11353075/how-can-i-maintain-fragment-state-when-added-to-the-back-stack/19022550#19022550            supportFragmentManager.executePendingTransactions();
         }
-        mediaDetails.showImage(i);
+        mediaDetails.showImage(position);
         forceInitBackButton();
     }
 

app/src/main/java/fr/free/nrw/commons/explore/SearchActivity.java

@@ -191,7 +191,8 @@ public class SearchActivity extends NavigationBaseActivity
      * Open media detail pager fragment on click of image in search results
      * @param index item index that should be opened
      */
-    public void onSearchImageClicked(int index) {
+    @Override
+    public void onMediaClicked(int index) {
         ViewUtil.hideKeyboard(this.findViewById(R.id.searchBox));
         toolbar.setVisibility(View.GONE);
         tabLayout.setVisibility(View.GONE);
@@ -263,15 +264,6 @@ public class SearchActivity extends NavigationBaseActivity
         viewPager.requestFocus();
     }
 
-    /**
-     * This method is called when viewPager has reached its end.
-     * Fetches more images using search query and adds it to the recycler view and viewpager adapter
-     */
-    @Override
-    public void requestMoreImages() {
-        //unneeded
-    }
-
     @Override protected void onDestroy() {
         super.onDestroy();
         //Dispose the disposables when the activity is destroyed

app/src/main/java/fr/free/nrw/commons/explore/categories/CategoriesModule.kt

@@ -4,12 +4,24 @@ import dagger.Binds
 import dagger.Module
 import fr.free.nrw.commons.explore.categories.media.CategoryMediaPresenter
 import fr.free.nrw.commons.explore.categories.media.CategoryMediaPresenterImpl
+import fr.free.nrw.commons.explore.categories.parent.ParentCategoriesPresenter
+import fr.free.nrw.commons.explore.categories.parent.ParentCategoriesPresenterImpl
+import fr.free.nrw.commons.explore.categories.sub.SubCategoriesPresenter
+import fr.free.nrw.commons.explore.categories.sub.SubCategoriesPresenterImpl
 
 
 @Module
 abstract class CategoriesModule {
 
     @Binds
-    abstract fun CategoryMediaPresenterImpl.bindsParentDepictionPresenter()
+    abstract fun CategoryMediaPresenterImpl.bindsCategoryMediaPresenter()
             : CategoryMediaPresenter
+
+    @Binds
+    abstract fun SubCategoriesPresenterImpl.bindsSubCategoriesPresenter()
+            : SubCategoriesPresenter
+
+    @Binds
+    abstract fun ParentCategoriesPresenterImpl.bindsParentCategoriesPresenter()
+            : ParentCategoriesPresenter
 }

app/src/main/java/fr/free/nrw/commons/explore/categories/PageableCategoryFragment.kt

@@ -0,0 +1,15 @@
+package fr.free.nrw.commons.explore.categories
+
+import fr.free.nrw.commons.R
+import fr.free.nrw.commons.category.CategoryDetailsActivity
+import fr.free.nrw.commons.explore.paging.BasePagingFragment
+
+
+abstract class PageableCategoryFragment : BasePagingFragment<String>() {
+    override val errorTextId: Int = R.string.error_loading_categories
+    override val pagedListAdapter by lazy {
+        PagedSearchCategoriesAdapter {
+            CategoryDetailsActivity.startYourself(context, it)
+        }
+    }
+}

app/src/main/java/fr/free/nrw/commons/explore/categories/PagedCategoriesAdapter.kt

@@ -1,4 +1,4 @@
-package fr.free.nrw.commons.explore.categories.search
+package fr.free.nrw.commons.explore.categories
 
 import android.view.View
 import android.view.ViewGroup
@@ -41,5 +41,3 @@ class CategoryItemViewHolder(containerView: View, val onCategoryClicked: (String
         textView1.text = item.substringAfter(CATEGORY_PREFIX)
     }
 }
-
-

app/src/main/java/fr/free/nrw/commons/explore/categories/media/CategoriesMediaFragment.kt

@@ -3,8 +3,6 @@ package fr.free.nrw.commons.explore.categories.media
 import android.os.Bundle
 import android.view.View
 import fr.free.nrw.commons.category.CATEGORY_PREFIX
-import fr.free.nrw.commons.category.CategoryDetailsActivity
-import fr.free.nrw.commons.category.CategoryImagesCallback
 import fr.free.nrw.commons.explore.media.PageableMediaFragment
 import javax.inject.Inject
 
@@ -20,12 +18,4 @@ class CategoriesMediaFragment : PageableMediaFragment() {
         super.onViewCreated(view, savedInstanceState)
         onQueryUpdated("$CATEGORY_PREFIX${arguments!!.getString("categoryName")!!}")
     }
-
-    override fun onItemClicked(position: Int) {
-        (activity as CategoryDetailsActivity).onMediaClicked(position)
-    }
-
-    override fun notifyViewPager() {
-        (activity as CategoryImagesCallback).viewPagerNotifyDataSetChanged()
-    }
 }

app/src/main/java/fr/free/nrw/commons/explore/categories/parent/PageableParentCategoriesDataSource.kt

@@ -0,0 +1,19 @@
+package fr.free.nrw.commons.explore.categories.parent
+
+import fr.free.nrw.commons.category.CategoryClient
+import fr.free.nrw.commons.explore.paging.LiveDataConverter
+import fr.free.nrw.commons.explore.paging.PageableBaseDataSource
+import javax.inject.Inject
+
+class PageableParentCategoriesDataSource @Inject constructor(
+    liveDataConverter: LiveDataConverter,
+    val categoryClient: CategoryClient
+) : PageableBaseDataSource<String>(liveDataConverter) {
+
+    override val loadFunction = { loadSize: Int, startPosition: Int ->
+        if (startPosition == 0) {
+            categoryClient.resetParentCategoryContinuation(query)
+        }
+        categoryClient.getParentCategoryList(query).blockingGet()
+    }
+}

app/src/main/java/fr/free/nrw/commons/explore/categories/parent/ParentCategoriesFragment.kt

@@ -0,0 +1,26 @@
+package fr.free.nrw.commons.explore.categories.parent
+
+import android.os.Bundle
+import android.view.View
+import fr.free.nrw.commons.R
+import fr.free.nrw.commons.category.CATEGORY_PREFIX
+import fr.free.nrw.commons.explore.categories.PageableCategoryFragment
+import javax.inject.Inject
+
+
+class ParentCategoriesFragment : PageableCategoryFragment() {
+
+    @Inject
+    lateinit var presenter: ParentCategoriesPresenter
+
+    override val injectedPresenter
+        get() = presenter
+
+    override fun getEmptyText(query: String) = getString(R.string.no_parentcategory_found)
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+        onQueryUpdated("$CATEGORY_PREFIX${arguments!!.getString("categoryName")!!}")
+    }
+}
+

app/src/main/java/fr/free/nrw/commons/explore/categories/parent/ParentCategoriesPresenterImpl.kt

@@ -0,0 +1,17 @@
+package fr.free.nrw.commons.explore.categories.parent
+
+import fr.free.nrw.commons.di.CommonsApplicationModule
+import fr.free.nrw.commons.explore.paging.BasePagingPresenter
+import fr.free.nrw.commons.explore.paging.PagingContract
+import io.reactivex.Scheduler
+import javax.inject.Inject
+import javax.inject.Named
+
+
+interface ParentCategoriesPresenter : PagingContract.Presenter<String>
+
+class ParentCategoriesPresenterImpl @Inject constructor(
+    @Named(CommonsApplicationModule.MAIN_THREAD) mainThreadScheduler: Scheduler,
+    dataSourceFactory: PageableParentCategoriesDataSource
+) : BasePagingPresenter<String>(mainThreadScheduler, dataSourceFactory),
+    ParentCategoriesPresenter

app/src/main/java/fr/free/nrw/commons/explore/categories/search/PageableSearchCategoriesDataSource.kt

@@ -5,12 +5,12 @@ import fr.free.nrw.commons.explore.paging.LiveDataConverter
 import fr.free.nrw.commons.explore.paging.PageableBaseDataSource
 import javax.inject.Inject
 
-class PageableCategoriesDataSource @Inject constructor(
+class PageableSearchCategoriesDataSource @Inject constructor(
     liveDataConverter: LiveDataConverter,
     val categoryClient: CategoryClient
 ) : PageableBaseDataSource<String>(liveDataConverter) {
 
     override val loadFunction = { loadSize: Int, startPosition: Int ->
-        categoryClient.searchCategories(query, loadSize, startPosition).blockingFirst()
+        categoryClient.searchCategories(query, loadSize, startPosition).blockingGet()
     }
 }

app/src/main/java/fr/free/nrw/commons/explore/categories/search/SearchCategoriesAdapter.kt

@@ -1,11 +0,0 @@
-package fr.free.nrw.commons.explore.categories.search
-
-import fr.free.nrw.commons.upload.categories.BaseDelegateAdapter
-
-
-class SearchCategoriesAdapter(onCateoryClicked: (String) -> Unit) : BaseDelegateAdapter<String>(
-    searchCategoryDelegate(
-        onCateoryClicked
-    ),
-    areItemsTheSame = { oldItem, newItem -> oldItem == newItem }
-)

app/src/main/java/fr/free/nrw/commons/explore/categories/search/SearchCategoriesAdapterDelegates.kt

@@ -1,15 +0,0 @@
-package fr.free.nrw.commons.explore.categories.search
-
-import com.hannesdorfmann.adapterdelegates4.dsl.adapterDelegateLayoutContainer
-import fr.free.nrw.commons.R
-import fr.free.nrw.commons.category.CATEGORY_PREFIX
-import kotlinx.android.synthetic.main.item_recent_searches.*
-
-
-fun searchCategoryDelegate(onCategoryClicked: (String) -> Unit) =
-    adapterDelegateLayoutContainer<String, String>(R.layout.item_recent_searches) {
-        containerView.setOnClickListener { onCategoryClicked(item) }
-        bind {
-            textView1.text = item.substringAfter(CATEGORY_PREFIX)
-        }
-    }

app/src/main/java/fr/free/nrw/commons/explore/categories/search/SearchCategoriesFragmentPresenterImpl.kt

@@ -11,6 +11,6 @@ interface SearchCategoriesFragmentPresenter : PagingContract.Presenter<String>
 
 class SearchCategoriesFragmentPresenterImpl @Inject constructor(
     @Named(CommonsApplicationModule.MAIN_THREAD) mainThreadScheduler: Scheduler,
-    dataSourceFactory: PageableCategoriesDataSource
+    dataSourceFactory: PageableSearchCategoriesDataSource
 ) : BasePagingPresenter<String>(mainThreadScheduler, dataSourceFactory),
     SearchCategoriesFragmentPresenter

app/src/main/java/fr/free/nrw/commons/explore/categories/search/SearchCategoryFragment.kt

@@ -1,27 +1,18 @@
 package fr.free.nrw.commons.explore.categories.search
 
 import fr.free.nrw.commons.R
-import fr.free.nrw.commons.category.CategoryDetailsActivity
+import fr.free.nrw.commons.explore.categories.PageableCategoryFragment
-import fr.free.nrw.commons.explore.paging.BasePagingFragment
 import javax.inject.Inject
 
 /**
  * Displays the category search screen.
  */
-class SearchCategoryFragment : BasePagingFragment<String>() {
+class SearchCategoryFragment : PageableCategoryFragment() {
     @Inject
     lateinit var presenter: SearchCategoriesFragmentPresenter
 
-    override val errorTextId: Int = R.string.error_loading_categories
-
     override val injectedPresenter
         get() = presenter
 
-    override val pagedListAdapter by lazy {
-        PagedSearchCategoriesAdapter {
-            CategoryDetailsActivity.startYourself(context, it)
-        }
-    }
-
     override fun getEmptyText(query: String) = getString(R.string.categories_not_found, query)
 }

app/src/main/java/fr/free/nrw/commons/explore/categories/sub/PageableSubCategoriesDataSource.kt

@@ -0,0 +1,19 @@
+package fr.free.nrw.commons.explore.categories.sub
+
+import fr.free.nrw.commons.category.CategoryClient
+import fr.free.nrw.commons.explore.paging.LiveDataConverter
+import fr.free.nrw.commons.explore.paging.PageableBaseDataSource
+import javax.inject.Inject
+
+class PageableSubCategoriesDataSource @Inject constructor(
+    liveDataConverter: LiveDataConverter,
+    val categoryClient: CategoryClient
+) : PageableBaseDataSource<String>(liveDataConverter) {
+
+    override val loadFunction = { loadSize: Int, startPosition: Int ->
+        if (startPosition == 0) {
+            categoryClient.resetSubCategoryContinuation(query)
+        }
+        categoryClient.getSubCategoryList(query).blockingGet()
+    }
+}

app/src/main/java/fr/free/nrw/commons/explore/categories/sub/SubCategoriesFragment.kt

@@ -0,0 +1,24 @@
+package fr.free.nrw.commons.explore.categories.sub
+
+import android.os.Bundle
+import android.view.View
+import fr.free.nrw.commons.R
+import fr.free.nrw.commons.category.CATEGORY_PREFIX
+import fr.free.nrw.commons.explore.categories.PageableCategoryFragment
+import javax.inject.Inject
+
+
+class SubCategoriesFragment : PageableCategoryFragment() {
+
+    @Inject lateinit var presenter: SubCategoriesPresenter
+
+    override val injectedPresenter
+        get() = presenter
+
+    override fun getEmptyText(query: String) = getString(R.string.no_subcategory_found)
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+        onQueryUpdated("$CATEGORY_PREFIX${arguments!!.getString("categoryName")!!}")
+    }
+}

app/src/main/java/fr/free/nrw/commons/explore/categories/sub/SubCategoriesPresenterImpl.kt

@@ -0,0 +1,16 @@
+package fr.free.nrw.commons.explore.categories.sub
+
+import fr.free.nrw.commons.di.CommonsApplicationModule
+import fr.free.nrw.commons.explore.paging.BasePagingPresenter
+import fr.free.nrw.commons.explore.paging.PagingContract
+import io.reactivex.Scheduler
+import javax.inject.Inject
+import javax.inject.Named
+
+interface SubCategoriesPresenter : PagingContract.Presenter<String>
+
+class SubCategoriesPresenterImpl @Inject constructor(
+    @Named(CommonsApplicationModule.MAIN_THREAD) mainThreadScheduler: Scheduler,
+    dataSourceFactory: PageableSubCategoriesDataSource
+) : BasePagingPresenter<String>(mainThreadScheduler, dataSourceFactory),
+    SubCategoriesPresenter

app/src/main/java/fr/free/nrw/commons/explore/depictions/WikidataItemDetailsActivity.java

@@ -13,6 +13,7 @@ import butterknife.ButterKnife;
 import com.google.android.material.tabs.TabLayout;
 import fr.free.nrw.commons.Media;
 import fr.free.nrw.commons.R;
+import fr.free.nrw.commons.category.CategoryImagesCallback;
 import fr.free.nrw.commons.explore.depictions.child.ChildDepictionsFragment;
 import fr.free.nrw.commons.explore.depictions.media.DepictedImagesFragment;
 import fr.free.nrw.commons.explore.depictions.parent.ParentDepictionsFragment;
@@ -26,7 +27,8 @@ import java.util.List;
 /**
  * Activity to show depiction media, parent classes and child classes of depicted items in Explore
  */
-public class WikidataItemDetailsActivity extends NavigationBaseActivity implements MediaDetailPagerFragment.MediaDetailProvider {
+public class WikidataItemDetailsActivity extends NavigationBaseActivity implements MediaDetailPagerFragment.MediaDetailProvider,
+    CategoryImagesCallback {
     private FragmentManager supportFragmentManager;
     private DepictedImagesFragment depictionImagesListFragment;
     private MediaDetailPagerFragment mediaDetailPagerFragment;
@@ -73,13 +75,13 @@ public class WikidataItemDetailsActivity extends NavigationBaseActivity implemen
      * This method is called on success of API call for featured Images.
      * The viewpager will notified that number of items have changed.
      */
+    @Override
     public void viewPagerNotifyDataSetChanged() {
         if (mediaDetailPagerFragment !=null){
             mediaDetailPagerFragment.notifyDataSetChanged();
         }
     }
 
-
     /**
      * This activity contains 3 tabs and a viewpager. This method is used to set the titles of tab,
      * Set the fragments according to the tab selected in the viewPager.

app/src/main/java/fr/free/nrw/commons/explore/depictions/media/DepictedImagesFragment.kt

@@ -17,12 +17,4 @@ class DepictedImagesFragment : PageableMediaFragment() {
         super.onViewCreated(view, savedInstanceState)
         onQueryUpdated(arguments!!.getString("entityId")!!)
     }
-
-    override fun onItemClicked(position: Int) {
-        (activity as WikidataItemDetailsActivity).onMediaClicked(position)
-    }
-
-    override fun notifyViewPager() {
-        (activity as WikidataItemDetailsActivity).viewPagerNotifyDataSetChanged()
-    }
 }

app/src/main/java/fr/free/nrw/commons/explore/media/PageableMediaFragment.kt

@@ -1,25 +1,35 @@
 package fr.free.nrw.commons.explore.media
 
+import android.content.Context
 import android.os.Bundle
 import android.view.View
 import fr.free.nrw.commons.Media
 import fr.free.nrw.commons.R
+import fr.free.nrw.commons.category.CategoryImagesCallback
 import fr.free.nrw.commons.explore.paging.BasePagingFragment
+import fr.free.nrw.commons.media.MediaDetailPagerFragment.MediaDetailProvider
 import kotlinx.android.synthetic.main.fragment_search_paginated.*
 
 
-abstract class PageableMediaFragment : BasePagingFragment<Media>() {
+abstract class PageableMediaFragment : BasePagingFragment<Media>(), MediaDetailProvider {
-    override val pagedListAdapter by lazy { PagedMediaAdapter(::onItemClicked) }
+
+    override val pagedListAdapter by lazy {
+        PagedMediaAdapter(categoryImagesCallback::onMediaClicked)
+    }
 
     override val errorTextId: Int = R.string.error_loading_images
 
     override fun getEmptyText(query: String) = getString(R.string.no_images_found)
 
-    protected abstract fun onItemClicked(position: Int)
+    lateinit var categoryImagesCallback: CategoryImagesCallback
 
-    protected abstract fun notifyViewPager()
+    override fun onAttach(context: Context) {
+        super.onAttach(context)
+        categoryImagesCallback = (context as CategoryImagesCallback)
+    }
 
-    private val simpleDataObserver = SimpleDataObserver { notifyViewPager() }
+    private val simpleDataObserver =
+        SimpleDataObserver { categoryImagesCallback.viewPagerNotifyDataSetChanged() }
 
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
@@ -31,12 +41,12 @@ abstract class PageableMediaFragment : BasePagingFragment<Media>() {
         pagedListAdapter.unregisterAdapterDataObserver(simpleDataObserver)
     }
 
-    fun getMediaAtPosition(position: Int): Media? =
+    override fun getMediaAtPosition(position: Int): Media? =
         pagedListAdapter.currentList?.get(position)?.takeIf { it.filename != null }
             .also {
                 pagedListAdapter.currentList?.loadAround(position)
                 paginatedSearchResultsList.scrollToPosition(position)
             }
 
-    fun getTotalMediaCount(): Int = pagedListAdapter.itemCount
+    override fun getTotalMediaCount(): Int = pagedListAdapter.itemCount
 }

app/src/main/java/fr/free/nrw/commons/explore/media/SearchMediaFragment.kt

@@ -1,7 +1,5 @@
 package fr.free.nrw.commons.explore.media
 
-import fr.free.nrw.commons.category.CategoryImagesCallback
-import fr.free.nrw.commons.explore.SearchActivity
 import javax.inject.Inject
 
 /**
@@ -13,14 +11,5 @@ class SearchMediaFragment : PageableMediaFragment(){
 
     override val injectedPresenter
         get() = presenter
-
-    override fun onItemClicked(position: Int) {
-        (context as SearchActivity).onSearchImageClicked(position)
-    }
-
-    override fun notifyViewPager() {
-        (activity as CategoryImagesCallback).viewPagerNotifyDataSetChanged()
-    }
-
 }
 

app/src/main/java/fr/free/nrw/commons/media/MediaClient.kt

@@ -2,6 +2,7 @@ package fr.free.nrw.commons.media
 
 import fr.free.nrw.commons.BuildConfig
 import fr.free.nrw.commons.Media
+import fr.free.nrw.commons.category.ContinuationClient
 import fr.free.nrw.commons.explore.media.MediaConverter
 import fr.free.nrw.commons.utils.CommonsDateUtil
 import io.reactivex.Single
@@ -24,14 +25,10 @@ class MediaClient @Inject constructor(
     private val pageMediaInterface: PageMediaInterface,
     private val mediaDetailInterface: MediaDetailInterface,
     private val mediaConverter: MediaConverter
-) {
+) : ContinuationClient<MwQueryResponse, Media>() {
 
     fun getMediaById(id: String) =
-        responseToMediaList(mediaInterface.getMediaById(id)).map { it.first() }
+        responseMapper(mediaInterface.getMediaById(id)).map { it.first() }
-
-    //OkHttpJsonApiClient used JsonKvStore for this. I don't know why.
-    private val continuationStore: MutableMap<String, Map<String, String>?> = mutableMapOf()
-    private val continuationExists: MutableMap<String, Boolean> = mutableMapOf()
 
     /**
      * Checks if a page exists on Commons
@@ -62,18 +59,8 @@ class MediaClient @Inject constructor(
      * @return
      */
     fun getMediaListFromCategory(category: String): Single<List<Media>> {
-        val key = "$CATEGORY_CONTINUATION_PREFIX$category"
+        return continuationRequest(CATEGORY_CONTINUATION_PREFIX, category) {
-        return if (hasMorePagesFor(key)) {
+            mediaInterface.getMediaListFromCategory(category, 10, it)
-            responseToMediaList(
-                mediaInterface.getMediaListFromCategory(
-                    category,
-                    10,
-                    continuationStore[key] ?: emptyMap()
-                ),
-                key
-            )
-        } else {
-            Single.just(emptyList())
         }
     }
 
@@ -86,16 +73,10 @@ class MediaClient @Inject constructor(
      * @return
      */
     fun getMediaListForUser(userName: String): Single<List<Media>> {
-        return responseToMediaList(
+        return continuationRequest("user_", userName) {
-            mediaInterface.getMediaListForUser(
+            mediaInterface.getMediaListForUser(userName, 10, it)
-                userName,
+        }
-                10,
-                continuationStore["user_$userName"] ?: Collections.emptyMap()
-            ),
-            "user_$userName"
-        )
     }
-
 
     /**
      * This method takes a keyword as input and returns a list of  Media objects filtered using image generator query
@@ -107,7 +88,7 @@ class MediaClient @Inject constructor(
      * @return
      */
     fun getMediaListFromSearch(keyword: String?, limit: Int, offset: Int) =
-        responseToMediaList(mediaInterface.getMediaListFromSearch(keyword, limit, offset))
+        responseMapper(mediaInterface.getMediaListFromSearch(keyword, limit, offset))
 
     /**
      * @return list of images for a particular depict entity
@@ -117,7 +98,7 @@ class MediaClient @Inject constructor(
         srlimit: Int,
         sroffset: Int
     ): Single<List<Media>> {
-        return responseToMediaList(
+        return responseMapper(
             mediaInterface.fetchImagesForDepictedItem(
                 "haswbstatement:" + BuildConfig.DEPICTS_PROPERTY + "=" + query,
                 srlimit.toString(),
@@ -126,23 +107,6 @@ class MediaClient @Inject constructor(
         )
     }
 
-    private fun responseToMediaList(
-        response: Single<MwQueryResponse>,
-        key: String? = null
-    ): Single<List<Media>> {
-        return response.map {
-            if (key != null) {
-                continuationExists[key] =
-                    it.continuation()?.let { continuation ->
-                        continuationStore[key] = continuation
-                        true
-                    } ?: false
-            }
-            it.query()?.pages() ?: emptyList()
-        }.flatMap(::mediaFromPageAndEntity)
-
-    }
-
     private fun mediaFromPageAndEntity(pages: List<MwQueryPage>): Single<List<Media>> {
         return if (pages.isEmpty())
             Single.just(emptyList())
@@ -165,7 +129,7 @@ class MediaClient @Inject constructor(
      * @return
      */
     fun getMedia(titles: String?): Single<Media> {
-        return responseToMediaList(mediaInterface.getMedia(titles))
+        return responseMapper(mediaInterface.getMedia(titles))
             .map { it.first() }
     }
 
@@ -176,7 +140,7 @@ class MediaClient @Inject constructor(
      */
     fun getPictureOfTheDay(): Single<Media> {
         val date = CommonsDateUtil.getIso8601DateFormatShort().format(Date())
-        return responseToMediaList(mediaInterface.getMediaWithGenerator("Template:Potd/$date")).map { it.first() }
+        return responseMapper(mediaInterface.getMediaWithGenerator("Template:Potd/$date")).map { it.first() }
 
     }
 
@@ -193,23 +157,22 @@ class MediaClient @Inject constructor(
     }
 
 
-    /**
-     * Check if media for user has reached the end of the list.
-     * @param userName
-     * @return
-     */
-    fun doesMediaListForUserHaveMorePages(userName: String): Boolean {
-        return hasMorePagesFor("user_$userName")
-    }
-
-    private fun hasMorePagesFor(key: String) = continuationExists[key] ?: true
-
     fun doesPageContainMedia(title: String?): Single<Boolean> {
         return pageMediaInterface.getMediaList(title)
             .map { it.items.isNotEmpty() }
     }
 
     fun resetCategoryContinuation(category: String) {
-        continuationExists.remove("$CATEGORY_CONTINUATION_PREFIX$category")
+        resetContinuation(CATEGORY_CONTINUATION_PREFIX, category)
+    }
+
+    override fun responseMapper(
+        networkResult: Single<MwQueryResponse>,
+        key: String?
+    ): Single<List<Media>> {
+        return networkResult.map {
+            handleContinuationResponse(it.continuation(), key)
+            it.query()?.pages() ?: emptyList()
+        }.flatMap(::mediaFromPageAndEntity)
     }
 }

app/src/main/java/fr/free/nrw/commons/media/MediaDetailPagerFragment.java

@@ -13,7 +13,6 @@ import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
-import android.widget.Toast;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
 import androidx.fragment.app.FragmentStatePagerAdapter;
@@ -26,7 +25,6 @@ import fr.free.nrw.commons.R;
 import fr.free.nrw.commons.bookmarks.Bookmark;
 import fr.free.nrw.commons.bookmarks.pictures.BookmarkPicturesContentProvider;
 import fr.free.nrw.commons.bookmarks.pictures.BookmarkPicturesDao;
-import fr.free.nrw.commons.category.CategoryImagesCallback;
 import fr.free.nrw.commons.contributions.Contribution;
 import fr.free.nrw.commons.di.CommonsDaggerSupportFragment;
 import fr.free.nrw.commons.utils.DownloadUtils;
@@ -269,8 +267,6 @@ public class MediaDetailPagerFragment extends CommonsDaggerSupportFragment imple
             Timber.d("Returning as activity is destroyed!");
             return;
         }
-        if (i+1 >= adapter.getCount() && getContext() instanceof CategoryImagesCallback)
-            ((CategoryImagesCallback) getContext()).requestMoreImages();
 
         getActivity().invalidateOptionsMenu();
     }

app/src/main/res/layout/fragment_browse_image.xml

@@ -1,44 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="match_parent"
-    android:layout_height="match_parent"
-    android:focusableInTouchMode="true"
-    android:id="@+id/image_search_results_display"
-    android:orientation="vertical"
-    android:paddingTop="@dimen/tiny_gap"
-    >
-
-    <TextView
-        android:id="@+id/imagesNotFound"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:gravity="center"
-        android:layout_centerInParent="true"
-        android:visibility="gone" />
-
-    <ProgressBar
-        android:id="@+id/bottomProgressBar"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:layout_centerHorizontal="true"
-        android:layout_alignParentBottom="true"
-        android:paddingTop="@dimen/tiny_padding"
-        android:paddingBottom="@dimen/tiny_padding"
-        android:visibility="gone"
-         />
-    <ProgressBar
-        android:id="@+id/imageSearchInProgress"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:layout_centerInParent="true"
-         />
-    <androidx.recyclerview.widget.RecyclerView
-        android:id="@+id/imagesListBox"
-        android:layout_width="match_parent"
-        android:layout_height="match_parent"
-        android:scrollbars="vertical"
-        android:layout_above="@+id/bottomProgressBar"
-        android:scrollbarSize="@dimen/standard_gap"
-        android:fadingEdge="none" />
-
-</RelativeLayout>

app/src/test/kotlin/fr/free/nrw/commons/category/CategoriesModelTest.kt

@@ -4,9 +4,8 @@ import categoryItem
 import com.nhaarman.mockitokotlin2.mock
 import com.nhaarman.mockitokotlin2.whenever
 import depictedItem
-import fr.free.nrw.commons.explore.depictions.DepictsClient
 import fr.free.nrw.commons.upload.GpsCategoryModel
-import io.reactivex.Observable
+import io.reactivex.Single
 import io.reactivex.subjects.BehaviorSubject
 import org.junit.Before
 import org.junit.Test
@@ -35,7 +34,7 @@ class CategoriesModelTest {
 
         val expectedList = listOf("Test")
         whenever(categoryClient.searchCategoriesForPrefix("tes", 25))
-            .thenReturn(Observable.just(expectedList))
+            .thenReturn(Single.just(expectedList))
 
         // Checking if both return "Test"
         val expectedItems = expectedList.map { CategoryItem(it, false) }
@@ -56,7 +55,7 @@ class CategoriesModelTest {
         whenever(gpsCategoryModel.categoriesFromLocation)
             .thenReturn(BehaviorSubject.createDefault(listOf("gpsCategory")))
         whenever(categoryClient.searchCategories("tes", 25))
-            .thenReturn(Observable.just(listOf("titleSearch")))
+            .thenReturn(Single.just(listOf("titleSearch")))
         whenever(categoryDao.recentCategories(25)).thenReturn(listOf("recentCategories"))
         CategoriesModel(categoryClient, categoryDao, gpsCategoryModel)
             .searchAll("", listOf("tes"), listOf(depictedItem))

app/src/test/kotlin/fr/free/nrw/commons/category/CategoryClientTest.kt

@@ -2,11 +2,10 @@ package fr.free.nrw.commons.category
 
 import com.nhaarman.mockitokotlin2.mock
 import com.nhaarman.mockitokotlin2.whenever
-import io.reactivex.Observable
+import io.reactivex.Single
 import org.junit.Before
 import org.junit.Test
-import org.mockito.ArgumentMatchers.anyInt
+import org.mockito.ArgumentMatchers.*
-import org.mockito.ArgumentMatchers.anyString
 import org.mockito.InjectMocks
 import org.mockito.Mock
 import org.mockito.Mockito.mock
@@ -32,7 +31,7 @@ class CategoryClientTest {
     fun searchCategoriesFound() {
         val mockResponse = withMockResponse("Category:Test")
         whenever(categoryInterface.searchCategories(anyString(), anyInt(), anyInt()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.searchCategories("tes", 10)
             .test()
             .assertValues(listOf("Test"))
@@ -45,7 +44,7 @@ class CategoryClientTest {
     fun searchCategoriesNull() {
         val mockResponse = withNullPages()
         whenever(categoryInterface.searchCategories(anyString(), anyInt(), anyInt()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.searchCategories("tes", 10)
             .test()
             .assertValues(emptyList())
@@ -58,7 +57,7 @@ class CategoryClientTest {
     fun searchCategoriesForPrefixFound() {
         val mockResponse = withMockResponse("Category:Test")
         whenever(categoryInterface.searchCategoriesForPrefix(anyString(), anyInt(), anyInt()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.searchCategoriesForPrefix("tes", 10)
             .test()
             .assertValues(listOf("Test"))
@@ -71,7 +70,7 @@ class CategoryClientTest {
     fun searchCategoriesForPrefixNull() {
         val mockResponse = withNullPages()
         whenever(categoryInterface.searchCategoriesForPrefix(anyString(), anyInt(), anyInt()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.searchCategoriesForPrefix("tes", 10)
             .test()
             .assertValues(emptyList())
@@ -83,8 +82,8 @@ class CategoryClientTest {
     @Test
     fun getParentCategoryListFound() {
         val mockResponse = withMockResponse("Category:Test")
-        whenever(categoryInterface.getParentCategoryList(anyString()))
+        whenever(categoryInterface.getParentCategoryList(anyString(), anyMap()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.getParentCategoryList("tes")
             .test()
             .assertValues(listOf("Test"))
@@ -93,8 +92,8 @@ class CategoryClientTest {
     @Test
     fun getParentCategoryListNull() {
         val mockResponse = withNullPages()
-        whenever(categoryInterface.getParentCategoryList(anyString()))
+        whenever(categoryInterface.getParentCategoryList(anyString(), anyMap()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.getParentCategoryList("tes")
             .test()
             .assertValues(emptyList())
@@ -103,8 +102,8 @@ class CategoryClientTest {
     @Test
     fun getSubCategoryListFound() {
         val mockResponse = withMockResponse("Category:Test")
-        whenever(categoryInterface.getSubCategoryList("tes"))
+        whenever(categoryInterface.getSubCategoryList("tes", emptyMap()))
-            .thenReturn(Observable.just(mockResponse))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.getSubCategoryList("tes")
             .test()
             .assertValues(listOf("Test"))
@@ -113,8 +112,11 @@ class CategoryClientTest {
     @Test
     fun getSubCategoryListNull() {
         val mockResponse = withNullPages()
-        whenever(categoryInterface.getSubCategoryList(anyString()))
+        whenever(categoryInterface.getSubCategoryList(
-            .thenReturn(Observable.just(mockResponse))
+            anyString(),
+            anyMap()
+        ))
+            .thenReturn(Single.just(mockResponse))
         categoryClient.getSubCategoryList("tes")
             .test()
             .assertValues(emptyList())

app/src/test/kotlin/fr/free/nrw/commons/contributions/ContributionBoundaryCallbackTest.kt

@@ -1,7 +1,9 @@
 package fr.free.nrw.commons.contributions
 
 import androidx.arch.core.executor.testing.InstantTaskExecutorRule
-import com.nhaarman.mockitokotlin2.*
+import com.nhaarman.mockitokotlin2.verify
+import com.nhaarman.mockitokotlin2.verifyZeroInteractions
+import com.nhaarman.mockitokotlin2.whenever
 import fr.free.nrw.commons.Media
 import fr.free.nrw.commons.auth.SessionManager
 import fr.free.nrw.commons.media.MediaClient
@@ -58,8 +60,6 @@ class ContributionBoundaryCallbackTest {
         whenever(mediaClient.getMediaListForUser(anyString())).thenReturn(
             Single.just(listOf(mock(Media::class.java)))
         )
-        whenever(mediaClient.doesMediaListForUserHaveMorePages(anyString()))
-            .thenReturn(true)
         contributionBoundaryCallback.onZeroItemsLoaded()
         verify(repository).save(anyList<Contribution>());
         verify(mediaClient).getMediaListForUser(anyString());
@@ -73,8 +73,6 @@ class ContributionBoundaryCallbackTest {
         whenever(mediaClient.getMediaListForUser(anyString())).thenReturn(
             Single.just(listOf(mock(Media::class.java)))
         )
-        whenever(mediaClient.doesMediaListForUserHaveMorePages(anyString()))
-            .thenReturn(true)
         contributionBoundaryCallback.onItemAtEndLoaded(mock(Contribution::class.java))
         verify(repository).save(anyList());
         verify(mediaClient).getMediaListForUser(anyString());
@@ -88,8 +86,6 @@ class ContributionBoundaryCallbackTest {
         whenever(mediaClient.getMediaListForUser(anyString())).thenReturn(
             Single.just(listOf(mock(Media::class.java)))
         )
-        whenever(mediaClient.doesMediaListForUserHaveMorePages(anyString()))
-            .thenReturn(true)
         contributionBoundaryCallback.onItemAtFrontLoaded(mock(Contribution::class.java))
         verify(repository).save(anyList());
         verify(mediaClient).getMediaListForUser(anyString());
@@ -103,28 +99,14 @@ class ContributionBoundaryCallbackTest {
         whenever(mediaClient.getMediaListForUser(anyString())).thenReturn(
             Single.just(listOf(mock(Media::class.java)))
         )
-        whenever(mediaClient.doesMediaListForUserHaveMorePages(anyString()))
-            .thenReturn(true)
         contributionBoundaryCallback.fetchContributions()
         verify(repository).save(anyList());
         verify(mediaClient).getMediaListForUser(anyString());
     }
 
-    @Test
-    fun testFetchContributionsForEndOfList() {
-        whenever(sessionManager.userName).thenReturn("Test")
-        whenever(mediaClient.doesMediaListForUserHaveMorePages(anyString()))
-            .thenReturn(false)
-        contributionBoundaryCallback.fetchContributions()
-        verify(mediaClient, times(0)).getMediaListForUser(anyString())
-        verifyNoMoreInteractions(repository)
-    }
-
     @Test
     fun testFetchContributionsFailed() {
         whenever(sessionManager.userName).thenReturn("Test")
-        whenever(mediaClient.doesMediaListForUserHaveMorePages(anyString()))
-            .thenReturn(true)
         whenever(mediaClient.getMediaListForUser(anyString())).thenReturn(Single.error(Exception("Error")))
         contributionBoundaryCallback.fetchContributions()
         verifyZeroInteractions(repository);

app/src/test/kotlin/fr/free/nrw/commons/explore/categories/parent/PageableParentCategoriesDataSourceTest.kt

@@ -0,0 +1,48 @@
+package fr.free.nrw.commons.explore.categories.parent
+
+import com.nhaarman.mockitokotlin2.never
+import com.nhaarman.mockitokotlin2.verify
+import com.nhaarman.mockitokotlin2.whenever
+import fr.free.nrw.commons.category.CategoryClient
+import fr.free.nrw.commons.explore.paging.LiveDataConverter
+import io.reactivex.Single
+import org.hamcrest.CoreMatchers.`is`
+import org.hamcrest.MatcherAssert.assertThat
+import org.junit.Before
+import org.junit.Test
+import org.mockito.Mock
+import org.mockito.MockitoAnnotations
+
+class PageableParentCategoriesDataSourceTest{
+    @Mock
+    lateinit var categoryClient: CategoryClient
+    @Mock
+    lateinit var liveDataConverter: LiveDataConverter
+
+    @Before
+    fun setUp() {
+        MockitoAnnotations.initMocks(this)
+    }
+
+    @Test
+    fun `loadFunction calls reset at position 0`() {
+        val dataSource =
+            PageableParentCategoriesDataSource(liveDataConverter, categoryClient)
+        dataSource.onQueryUpdated("test")
+        whenever(categoryClient.getParentCategoryList("test"))
+            .thenReturn(Single.just(emptyList()))
+        assertThat(dataSource.loadFunction(-1, 0), `is`(emptyList()))
+        verify(categoryClient).resetParentCategoryContinuation("test")
+    }
+
+    @Test
+    fun `loadFunction does not call reset at any other position`() {
+        val dataSource =
+            PageableParentCategoriesDataSource(liveDataConverter, categoryClient)
+        dataSource.onQueryUpdated("test")
+        whenever(categoryClient.getParentCategoryList("test"))
+            .thenReturn(Single.just(emptyList()))
+        assertThat(dataSource.loadFunction(-1, 1), `is`(emptyList()))
+        verify(categoryClient, never()).resetParentCategoryContinuation("test")
+    }
+}

app/src/test/kotlin/fr/free/nrw/commons/explore/categories/sub/PageableSubCategoriesDataSourceTest.kt

@@ -0,0 +1,48 @@
+package fr.free.nrw.commons.explore.categories.sub
+
+import com.nhaarman.mockitokotlin2.never
+import com.nhaarman.mockitokotlin2.verify
+import com.nhaarman.mockitokotlin2.whenever
+import fr.free.nrw.commons.category.CategoryClient
+import fr.free.nrw.commons.explore.paging.LiveDataConverter
+import io.reactivex.Single
+import org.hamcrest.CoreMatchers.`is`
+import org.hamcrest.MatcherAssert.assertThat
+import org.junit.Before
+import org.junit.Test
+import org.mockito.Mock
+import org.mockito.MockitoAnnotations
+
+class PageableSubCategoriesDataSourceTest{
+    @Mock
+    lateinit var categoryClient: CategoryClient
+    @Mock
+    lateinit var liveDataConverter: LiveDataConverter
+
+    @Before
+    fun setUp() {
+        MockitoAnnotations.initMocks(this)
+    }
+
+    @Test
+    fun `loadFunction calls reset at position 0`() {
+        val dataSource =
+            PageableSubCategoriesDataSource(liveDataConverter, categoryClient)
+        dataSource.onQueryUpdated("test")
+        whenever(categoryClient.getSubCategoryList("test"))
+            .thenReturn(Single.just(emptyList()))
+        assertThat(dataSource.loadFunction(-1, 0), `is`(emptyList()))
+        verify(categoryClient).resetSubCategoryContinuation("test")
+    }
+
+    @Test
+    fun `loadFunction does not call reset at any other position`() {
+        val dataSource =
+            PageableSubCategoriesDataSource(liveDataConverter, categoryClient)
+        dataSource.onQueryUpdated("test")
+        whenever(categoryClient.getSubCategoryList("test"))
+            .thenReturn(Single.just(emptyList()))
+        assertThat(dataSource.loadFunction(-1, 1), `is`(emptyList()))
+        verify(categoryClient, never()).resetSubCategoryContinuation("test")
+    }
+}

app/src/test/kotlin/fr/free/nrw/commons/explore/categroies/PageableSearchCategoriesDataSourceTest.kt

@@ -3,19 +3,20 @@ package fr.free.nrw.commons.explore.categroies
 import com.nhaarman.mockitokotlin2.mock
 import com.nhaarman.mockitokotlin2.whenever
 import fr.free.nrw.commons.category.CategoryClient
-import fr.free.nrw.commons.explore.categories.search.PageableCategoriesDataSource
+import fr.free.nrw.commons.explore.categories.search.PageableSearchCategoriesDataSource
-import io.reactivex.Observable
+import io.reactivex.Single
 import org.hamcrest.MatcherAssert.assertThat
 import org.hamcrest.Matchers
 import org.junit.Test
 
-class PageableCategoriesDataSourceTest {
+class PageableSearchCategoriesDataSourceTest {
     @Test
     fun `loadFunction loads categories`() {
         val categoryClient: CategoryClient = mock()
         whenever(categoryClient.searchCategories("test", 0, 1))
-            .thenReturn(Observable.just(emptyList()))
+            .thenReturn(Single.just(emptyList()))
-        val pageableCategoriesDataSource = PageableCategoriesDataSource(mock(), categoryClient)
+        val pageableCategoriesDataSource =
+            PageableSearchCategoriesDataSource(mock(), categoryClient)
         pageableCategoriesDataSource.onQueryUpdated("test")
         assertThat(pageableCategoriesDataSource.loadFunction(0, 1), Matchers.`is`(emptyList()))
     }