Merge pull request #834 from akaita/667_fix_categories

667 fix categories

app/build.gradle

@@ -17,7 +17,7 @@ dependencies {
     compile "com.android.support:design:${project.supportLibVersion}"
     compile 'com.google.code.gson:gson:2.8.0'
     compile "com.jakewharton:butterknife:$BUTTERKNIFE_VERSION"
-    compile 'com.github.pedrovgs:renderers:3.3.0'
+    compile 'com.github.pedrovgs:renderers:3.3.3'
     annotationProcessor "com.jakewharton:butterknife-compiler:$BUTTERKNIFE_VERSION"
     compile 'com.jakewharton.timber:timber:4.5.1'
     compile 'com.squareup.okhttp3:okhttp:3.8.1'
@@ -30,7 +30,10 @@ dependencies {
     // Because RxAndroid releases are few and far between, it is recommended you also
     // explicitly depend on RxJava's latest version for bug fixes and new features.
     compile 'io.reactivex.rxjava2:rxjava:2.1.2'
-
+    compile 'com.jakewharton.rxbinding2:rxbinding:2.0.0'
+    compile 'com.jakewharton.rxbinding2:rxbinding-support-v4:2.0.0'
+    compile 'com.jakewharton.rxbinding2:rxbinding-appcompat-v7:2.0.0'
+    compile 'com.jakewharton.rxbinding2:rxbinding-design:2.0.0'
 
     compile 'com.facebook.fresco:fresco:1.3.0'
     compile 'com.facebook.stetho:stetho:1.5.0'

app/src/main/java/fr/free/nrw/commons/CommonsApplication.java

@@ -25,8 +25,8 @@ import java.io.IOException;
 
 import fr.free.nrw.commons.auth.AccountUtil;
 import fr.free.nrw.commons.caching.CacheController;
-import fr.free.nrw.commons.category.Category;
 import fr.free.nrw.commons.contributions.Contribution;
+import fr.free.nrw.commons.data.Category;
 import fr.free.nrw.commons.data.DBOpenHelper;
 import fr.free.nrw.commons.modifications.ModifierSequence;
 import fr.free.nrw.commons.mwapi.ApacheHttpClientMediaWikiApi;

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

@@ -2,18 +2,13 @@ package fr.free.nrw.commons.category;
 
 import android.content.ContentProviderClient;
 import android.content.SharedPreferences;
-import android.database.Cursor;
-import android.os.AsyncTask;
 import android.os.Bundle;
-import android.os.RemoteException;
 import android.preference.PreferenceManager;
 import android.support.v4.app.Fragment;
 import android.support.v7.app.AlertDialog;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
-import android.text.Editable;
 import android.text.TextUtils;
-import android.text.TextWatcher;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuInflater;
@@ -24,24 +19,26 @@ import android.widget.EditText;
 import android.widget.ProgressBar;
 import android.widget.TextView;
 
-import com.pedrogomez.renderers.ListAdapteeCollection;
+import com.jakewharton.rxbinding2.view.RxView;
+import com.jakewharton.rxbinding2.widget.RxTextView;
 import com.pedrogomez.renderers.RVRendererAdapter;
 
 import java.util.ArrayList;
+import java.util.Calendar;
+import java.util.Date;
 import java.util.HashMap;
-import java.util.HashSet;
-import java.util.LinkedHashSet;
 import java.util.List;
-import java.util.Set;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.ScheduledThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 
 import butterknife.BindView;
 import butterknife.ButterKnife;
+import fr.free.nrw.commons.CommonsApplication;
 import fr.free.nrw.commons.R;
-import fr.free.nrw.commons.category.CategoriesRenderer.CategoryClickedListener;
+import fr.free.nrw.commons.data.Category;
 import fr.free.nrw.commons.upload.MwVolleyApi;
+import io.reactivex.Observable;
+import io.reactivex.android.schedulers.AndroidSchedulers;
+import io.reactivex.schedulers.Schedulers;
 import timber.log.Timber;
 
 import static android.view.KeyEvent.ACTION_UP;
@@ -51,7 +48,8 @@ import static fr.free.nrw.commons.category.CategoryContentProvider.AUTHORITY;
 /**
  * Displays the category suggestion and selection screen. Category search is initiated here.
  */
-public class CategorizationFragment extends Fragment implements CategoryClickedListener {
+public class CategorizationFragment extends Fragment {
+
     public static final int SEARCH_CATS_LIMIT = 25;
 
     @BindView(R.id.categoriesListBox)
@@ -68,19 +66,18 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
     private RVRendererAdapter<CategoryItem> categoriesAdapter;
     private OnCategoriesSaveHandler onCategoriesSaveHandler;
     private HashMap<String, ArrayList<String>> categoriesCache;
-    private ArrayList<String> selectedCategories = new ArrayList<>();
+    private List<CategoryItem> selectedCategories = new ArrayList<>();
-    private ContentProviderClient client;
+    private ContentProviderClient databaseClient;
-    private PrefixUpdater prefixUpdaterSub;
+
-    private MethodAUpdater methodAUpdaterSub;
+    private final CategoriesAdapterFactory adapterFactory = new CategoriesAdapterFactory(item -> {
-    private final CategoryTextWatcher textWatcher = new CategoryTextWatcher();
+        if (item.isSelected()) {
-    private final CategoriesAdapterFactory adapterFactory = new CategoriesAdapterFactory(this);
+            selectedCategories.add(item);
-    private final ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(2);
+            updateCategoryCount(item, databaseClient);
-    private final ArrayList<String> titleCatItems = new ArrayList<>();
+        } else {
-    private final CountDownLatch mergeLatch = new CountDownLatch(1);
+            selectedCategories.remove(item);
-    // LHS guarantees ordered insertions, allowing for prioritized method A results
+        }
-    private final Set<String> results = new LinkedHashSet<>();
+    });
 
-    @SuppressWarnings("unchecked")
     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
                              Bundle savedInstanceState) {
@@ -89,27 +86,29 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
 
         categoriesList.setLayoutManager(new LinearLayoutManager(getContext()));
 
-        categoriesSkip.setOnClickListener(view -> {
+        RxView.clicks(categoriesSkip)
-            getActivity().onBackPressed();
+                .takeUntil(RxView.detaches(categoriesSkip))
-            getActivity().finish();
+                .subscribe(o -> {
-        });
+                    getActivity().onBackPressed();
+                    getActivity().finish();
+                });
 
-        ArrayList<CategoryItem> items;
+        ArrayList<CategoryItem> items = new ArrayList<>();
-        if (savedInstanceState == null) {
+        categoriesCache = new HashMap<>();
-            items = new ArrayList<>();
+        if (savedInstanceState != null) {
-            categoriesCache = new HashMap<>();
+            items.addAll(savedInstanceState.getParcelableArrayList("currentCategories"));
-        } else {
+            categoriesCache.putAll((HashMap<String, ArrayList<String>>) savedInstanceState
-            items = savedInstanceState.getParcelableArrayList("currentCategories");
+                    .getSerializable("categoriesCache"));
-            categoriesCache = (HashMap<String, ArrayList<String>>) savedInstanceState
-                    .getSerializable("categoriesCache");
         }
 
         categoriesAdapter = adapterFactory.create(items);
         categoriesList.setAdapter(categoriesAdapter);
-        categoriesFilter.addTextChangedListener(textWatcher);
-
-        startUpdatingCategoryList();
 
+        RxTextView.textChanges(categoriesFilter)
+                .takeUntil(RxView.detaches(categoriesFilter))
+                .debounce(300, TimeUnit.MILLISECONDS)
+                .observeOn(AndroidSchedulers.mainThread())
+                .subscribe(filter -> updateCategoryList(filter.toString()));
         return rootView;
     }
 
@@ -129,7 +128,7 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
             rootView.requestFocus();
             rootView.setOnKeyListener((v, keyCode, event) -> {
                 if (event.getAction() == ACTION_UP && keyCode == KEYCODE_BACK) {
-                    backButtonDialog();
+                    showBackButtonDialog();
                     return true;
                 }
                 return false;
@@ -137,16 +136,10 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
         }
     }
 
-    @Override
-    public void onDestroyView() {
-        categoriesFilter.removeTextChangedListener(textWatcher);
-        super.onDestroyView();
-    }
-
     @Override
     public void onDestroy() {
         super.onDestroy();
-        client.release();
+        databaseClient.release();
     }
 
     @Override
@@ -165,42 +158,17 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
     public boolean onOptionsItemSelected(MenuItem menuItem) {
         switch (menuItem.getItemId()) {
             case R.id.menu_save_categories:
-
+                if (selectedCategories.size() > 0) {
-                int numberSelected = 0;
+                    //Some categories selected, proceed to submission
-
+                    onCategoriesSaveHandler.onCategoriesSave(getStringList(selectedCategories));
-                selectedCategories = new ArrayList<>();
-                int count = categoriesAdapter.getItemCount();
-                for (int i = 0; i < count; i++) {
-                    CategoryItem item = categoriesAdapter.getItem(i);
-                    if (item.isSelected()) {
-                        selectedCategories.add(item.getName());
-                        numberSelected++;
-                    }
-                }
-
-                //If no categories selected, display warning to user
-                if (numberSelected == 0) {
-                    new AlertDialog.Builder(getActivity())
-                            .setMessage("Images without categories are rarely usable. "
-                                    + "Are you sure you want to submit without selecting "
-                                    + "categories?")
-                            .setTitle("No Categories Selected")
-                            .setPositiveButton("No, go back", (dialog, id) -> {
-                                //Exit menuItem so user can select their categories
-                            })
-                            .setNegativeButton("Yes, submit", (dialog, id) -> {
-                                //Proceed to submission
-                                onCategoriesSaveHandler.onCategoriesSave(selectedCategories);
-                            })
-                            .create()
-                            .show();
                 } else {
-                    //Proceed to submission
+                    //No categories selected, prompt the user to select some
-                    onCategoriesSaveHandler.onCategoriesSave(selectedCategories);
+                    showConfirmationDialog();
-                    return true;
                 }
+                return true;
+            default:
+                return super.onOptionsItemSelected(menuItem);
         }
-        return super.onOptionsItemSelected(menuItem);
     }
 
     @Override
@@ -209,249 +177,161 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
         setHasOptionsMenu(true);
         onCategoriesSaveHandler = (OnCategoriesSaveHandler) getActivity();
         getActivity().setTitle(R.string.categories_activity_title);
-        client = getActivity().getContentResolver().acquireContentProviderClient(AUTHORITY);
+        databaseClient = getActivity().getContentResolver().acquireContentProviderClient(AUTHORITY);
     }
 
-    public HashMap<String, ArrayList<String>> getCategoriesCache() {
+    private void updateCategoryList(String filter) {
-        return categoriesCache;
+        Observable.fromIterable(selectedCategories)
+                .subscribeOn(Schedulers.io())
+                .observeOn(AndroidSchedulers.mainThread())
+                .doOnSubscribe(disposable -> {
+                    categoriesSearchInProgress.setVisibility(View.VISIBLE);
+                    categoriesNotFoundView.setVisibility(View.GONE);
+                    categoriesSkip.setVisibility(View.GONE);
+                    categoriesAdapter.clear();
+                })
+                .observeOn(Schedulers.io())
+                .concatWith(
+                        searchAll(filter)
+                                .mergeWith(searchCategories(filter))
+                                .concatWith( TextUtils.isEmpty(filter)
+                                        ? defaultCategories() : Observable.empty())
+                )
+                .filter(categoryItem -> !containsYear(categoryItem.getName()))
+                .distinct()
+                .observeOn(AndroidSchedulers.mainThread())
+                .subscribe(
+                        s -> categoriesAdapter.add(s),
+                        throwable -> Timber.e(throwable),
+                        () -> {
+                            categoriesAdapter.notifyDataSetChanged();
+                            categoriesSearchInProgress.setVisibility(View.GONE);
+
+                            if (categoriesAdapter.getItemCount() == selectedCategories.size()) {
+                                // There are no suggestions
+                                if (TextUtils.isEmpty(filter)) {
+                                    // Allow to send image with no categories
+                                    categoriesSkip.setVisibility(View.VISIBLE);
+                                } else {
+                                    // Inform the user that the searched term matches  no category
+                                    categoriesNotFoundView.setText(getString(R.string.categories_not_found, filter));
+                                    categoriesNotFoundView.setVisibility(View.VISIBLE);
+                                }
+                            }
+                        }
+                );
     }
 
-    /**
+    private List<String> getStringList(List<CategoryItem> input) {
-     * Retrieves category suggestions from title input
+        List<String> output = new ArrayList<>();
-     *
+        for (CategoryItem item : input) {
-     * @return a list containing title-related categories
+            output.add(item.getName());
-     */
+        }
-    private ArrayList<String> titleCatQuery() {
+        return output;
-        TitleCategories titleCategoriesSub;
+    }
 
+    private Observable<CategoryItem> defaultCategories() {
+        return gpsCategories()
+                .concatWith(titleCategories())
+                .concatWith(recentCategories());
+    }
+
+    private Observable<CategoryItem> gpsCategories() {
+        return Observable.fromIterable(
+                MwVolleyApi.GpsCatExists.getGpsCatExists()
+                        ? MwVolleyApi.getGpsCat() : new ArrayList<>())
+                .map(name -> new CategoryItem(name, false));
+    }
+
+    private Observable<CategoryItem> titleCategories() {
         //Retrieve the title that was saved when user tapped submit icon
         SharedPreferences titleDesc = PreferenceManager.getDefaultSharedPreferences(getActivity());
         String title = titleDesc.getString("Title", "");
-        Timber.d("Title: %s", title);
 
-        //Override onPostExecute to access the results of async API call
+        return CommonsApplication.getInstance().getMWApi()
-        titleCategoriesSub = new TitleCategories(title) {
+                .searchTitles(title, SEARCH_CATS_LIMIT)
-            @Override
+                .map(name -> new CategoryItem(name, false));
-            protected void onPostExecute(List<String> result) {
-                super.onPostExecute(result);
-                Timber.d("Results in onPostExecute: %s", result);
-                titleCatItems.addAll(result);
-                Timber.d("TitleCatItems in onPostExecute: %s", titleCatItems);
-                mergeLatch.countDown();
-            }
-        };
-
-        titleCategoriesSub.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
-        Timber.d("TitleCatItems in titleCatQuery: %s", titleCatItems);
-
-        //Only return titleCatItems after API call has finished
-        try {
-            mergeLatch.await(5L, TimeUnit.SECONDS);
-        } catch (InterruptedException e) {
-            Timber.e(e, "Interrupted exception: ");
-        }
-        return titleCatItems;
     }
 
-    /**
+    private Observable<CategoryItem> recentCategories() {
-     * Retrieves recently-used categories
+        return Observable.fromIterable(Category.recentCategories(databaseClient, SEARCH_CATS_LIMIT))
-     *
+                .map(s -> new CategoryItem(s, false));
-     * @return a list containing recent categories
-     */
-    private ArrayList<String> recentCatQuery() {
-        ArrayList<String> items = new ArrayList<>();
-        Cursor cursor = null;
-        try {
-            cursor = client.query(
-                    CategoryContentProvider.BASE_URI,
-                    Category.Table.ALL_FIELDS,
-                    null,
-                    new String[]{},
-                    Category.Table.COLUMN_LAST_USED + " DESC");
-            // fixme add a limit on the original query instead of falling out of the loop?
-            while (cursor != null && cursor.moveToNext()
-                    && cursor.getPosition() < SEARCH_CATS_LIMIT) {
-                Category cat = Category.fromCursor(cursor);
-                items.add(cat.getName());
-            }
-        } catch (RemoteException e) {
-            throw new RuntimeException(e);
-        } finally {
-            if (cursor != null) {
-                cursor.close();
-            }
-        }
-        return items;
     }
 
-    /**
+    private Observable<CategoryItem> searchAll(String term) {
-     * Merges nearby categories, categories suggested based on title, and recent categories...
+        //If user hasn't typed anything in yet, get GPS and recent items
-     * without duplicates.
+        if (TextUtils.isEmpty(term)) {
-     *
+            return Observable.empty();
-     * @return a list containing merged categories
-     */
-    ArrayList<String> mergeItems() {
-        Set<String> mergedItems = new LinkedHashSet<>();
-
-        Timber.d("Calling APIs for GPS cats, title cats and recent cats...");
-
-        List<String> gpsItems = new ArrayList<>();
-        if (MwVolleyApi.GpsCatExists.getGpsCatExists()) {
-            gpsItems.addAll(MwVolleyApi.getGpsCat());
-        }
-        List<String> titleItems = new ArrayList<>(titleCatQuery());
-        List<String> recentItems = new ArrayList<>(recentCatQuery());
-
-        //Await results of titleItems, which is likely to come in last
-        try {
-            mergeLatch.await(5L, TimeUnit.SECONDS);
-            Timber.d("Waited for merge");
-        } catch (InterruptedException e) {
-            Timber.e(e, "Interrupted Exception: ");
         }
 
-        mergedItems.addAll(gpsItems);
+        //if user types in something that is in cache, return cached category
-        Timber.d("Adding GPS items: %s", gpsItems);
+        if (categoriesCache.containsKey(term)) {
-        mergedItems.addAll(titleItems);
+            return Observable.fromIterable(categoriesCache.get(term))
-        Timber.d("Adding title items: %s", titleItems);
+                    .map(name -> new CategoryItem(name, false));
-        mergedItems.addAll(recentItems);
+        }
-        Timber.d("Adding recent items: %s", recentItems);
 
-        // Needs to be an ArrayList and not a List unless we want to modify a big portion
+        //otherwise, search API for matching categories
-        // of preexisting code
+        return CommonsApplication.getInstance().getMWApi()
-        ArrayList<String> mergedItemsList = new ArrayList<>(mergedItems);
+                .allCategories(term, SEARCH_CATS_LIMIT)
-
+                .map(name -> new CategoryItem(name, false));
-        Timber.d("Merged item list: %s", mergedItemsList);
-        return mergedItemsList;
     }
 
-    /**
+    private Observable<CategoryItem> searchCategories(String term) {
-     * Displays categories found to the user as they type in the search box
+        //If user hasn't typed anything in yet, get GPS and recent items
-     *
+        if (TextUtils.isEmpty(term)) {
-     * @param categories a list of all categories found for the search string
+            return Observable.empty();
-     * @param filter     the search string
-     */
-    private void setCatsAfterAsync(ArrayList<String> categories, String filter) {
-        if (getActivity() != null) {
-            ArrayList<CategoryItem> items = new ArrayList<>();
-            HashSet<String> existingKeys = new HashSet<>();
-            int count = categoriesAdapter.getItemCount();
-            for (int i = 0; i < count; i++) {
-                CategoryItem item = categoriesAdapter.getItem(i);
-                if (item.isSelected()) {
-                    items.add(item);
-                    existingKeys.add(item.getName());
-                }
-            }
-            for (String category : categories) {
-                if (!existingKeys.contains(category)) {
-                    items.add(new CategoryItem(category, false));
-                }
-            }
-
-            categoriesAdapter.setCollection(new ListAdapteeCollection<>(items));
-            categoriesAdapter.notifyDataSetChanged();
-            categoriesSearchInProgress.setVisibility(View.GONE);
-
-            if (categories.isEmpty()) {
-                if (TextUtils.isEmpty(filter)) {
-                    // If we found no recent cats, show the skip message!
-                    categoriesSkip.setVisibility(View.VISIBLE);
-                } else {
-                    categoriesNotFoundView.setText(getString(R.string.categories_not_found, filter));
-                    categoriesNotFoundView.setVisibility(View.VISIBLE);
-                }
-            } else {
-                categoriesList.smoothScrollToPosition(existingKeys.size());
-            }
-        } else {
-            Timber.e("Error: Fragment is null");
         }
+
+        return CommonsApplication.getInstance().getMWApi()
+                .searchCategories(term, SEARCH_CATS_LIMIT)
+                .map(s -> new CategoryItem(s, false));
     }
 
+    private boolean containsYear(String item) {
+        //Check for current and previous year to exclude these categories from removal
+        Calendar now = Calendar.getInstance();
+        int year = now.get(Calendar.YEAR);
+        String yearInString = String.valueOf(year);
 
-    /**
+        int prevYear = year - 1;
-     * Makes asynchronous calls to the Commons MediaWiki API via anonymous subclasses of
+        String prevYearInString = String.valueOf(prevYear);
-     * 'MethodAUpdater' and 'PrefixUpdater'. Some of their methods are overridden in order to
+        Timber.d("Previous year: %s", prevYearInString);
-     * aggregate the results. A CountDownLatch is used to ensure that MethodA results are shown
-     * above Prefix results.
-     */
-    private void requestSearchResults() {
-        final CountDownLatch latch = new CountDownLatch(1);
 
-        prefixUpdaterSub = new PrefixUpdater(this) {
+        //Check if item contains a 4-digit word anywhere within the string (.* is wildcard)
-            @Override
+        //And that item does not equal the current year or previous year
-            protected List<String> doInBackground(Void... voids) {
+        //And if it is an irrelevant category such as Media_needing_categories_as_of_16_June_2017(Issue #750)
-                List<String> result = new ArrayList<>();
+        return ((item.matches(".*(19|20)\\d{2}.*") && !item.contains(yearInString) && !item.contains(prevYearInString))
-                try {
+                || item.matches("(.*)needing(.*)") || item.matches("(.*)taken on(.*)"));
-                    result = super.doInBackground();
-                    latch.await();
-                } catch (InterruptedException e) {
-                    Timber.w(e);
-                    //Thread.currentThread().interrupt();
-                }
-                return result;
-            }
-
-            @Override
-            protected void onPostExecute(List<String> result) {
-                super.onPostExecute(result);
-
-                results.addAll(result);
-                Timber.d("Prefix result: %s", result);
-
-                String filter = categoriesFilter.getText().toString();
-                ArrayList<String> resultsList = new ArrayList<>(results);
-                categoriesCache.put(filter, resultsList);
-                Timber.d("Final results List: %s", resultsList);
-
-                categoriesAdapter.notifyDataSetChanged();
-                setCatsAfterAsync(resultsList, filter);
-            }
-        };
-
-        methodAUpdaterSub = new MethodAUpdater(this) {
-            @Override
-            protected void onPostExecute(List<String> result) {
-                results.clear();
-                super.onPostExecute(result);
-
-                results.addAll(result);
-                Timber.d("Method A result: %s", result);
-                categoriesAdapter.notifyDataSetChanged();
-
-                latch.countDown();
-            }
-        };
-        prefixUpdaterSub.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
-        methodAUpdaterSub.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }
 
-    private void startUpdatingCategoryList() {
+    private void updateCategoryCount(CategoryItem item, ContentProviderClient client) {
-        if (prefixUpdaterSub != null) {
+        Category cat = lookupCategory(item.getName());
-            prefixUpdaterSub.cancel(true);
+        cat.incTimesUsed();
+        cat.save(client);
+    }
+
+    private Category lookupCategory(String name) {
+        Category cat = Category.find(databaseClient, name);
+
+        if (cat == null) {
+            // Newly used category...
+            cat = new Category();
+            cat.setName(name);
+            cat.setLastUsed(new Date());
+            cat.setTimesUsed(0);
         }
 
-        if (methodAUpdaterSub != null) {
+        return cat;
-            methodAUpdaterSub.cancel(true);
-        }
-
-        requestSearchResults();
     }
 
     public int getCurrentSelectedCount() {
-        int count = 0;
+        return selectedCategories.size();
-        int numberOfItems = categoriesAdapter.getItemCount();
-        for (int i = 0; i < numberOfItems; i++) {
-            CategoryItem item = categoriesAdapter.getItem(i);
-            if (item.isSelected()) {
-                count++;
-            }
-        }
-        return count;
     }
 
-    public void backButtonDialog() {
+    /**
+     * Show dialog asking for confirmation to leave without saving categories.
+     */
+    public void showBackButtonDialog() {
         new AlertDialog.Builder(getActivity())
                 .setMessage("Are you sure you want to go back? The image will not "
                         + "have any categories saved.")
@@ -464,26 +344,20 @@ public class CategorizationFragment extends Fragment implements CategoryClickedL
                 .show();
     }
 
-    @Override
+    private void showConfirmationDialog() {
-    public void categoryClicked(CategoryItem item) {
+        new AlertDialog.Builder(getActivity())
-        if (item.isSelected()) {
+                .setMessage("Images without categories are rarely usable. "
-            new CategoryCountUpdater(item.getName(), client).executeOnExecutor(executor);
+                        + "Are you sure you want to submit without selecting "
-        }
+                        + "categories?")
-    }
+                .setTitle("No Categories Selected")
-
+                .setPositiveButton("No, go back", (dialog, id) -> {
-    private class CategoryTextWatcher implements TextWatcher {
+                    //Exit menuItem so user can select their categories
-        @Override
+                })
-        public void beforeTextChanged(CharSequence charSequence, int i, int i2, int i3) {
+                .setNegativeButton("Yes, submit", (dialog, id) -> {
-        }
+                    //Proceed to submission
-
+                    onCategoriesSaveHandler.onCategoriesSave(getStringList(selectedCategories));
-        @Override
+                })
-        public void onTextChanged(CharSequence charSequence, int i, int i2, int i3) {
+                .create()
-            startUpdatingCategoryList();
+                .show();
-        }
-
-        @Override
-        public void afterTextChanged(Editable editable) {
-
-        }
     }
 }

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

@@ -11,6 +11,7 @@ import android.support.annotation.NonNull;
 import android.text.TextUtils;
 
 import fr.free.nrw.commons.CommonsApplication;
+import fr.free.nrw.commons.data.Category;
 import fr.free.nrw.commons.data.DBOpenHelper;
 import timber.log.Timber;
 

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

@@ -1,59 +0,0 @@
-package fr.free.nrw.commons.category;
-
-import android.content.ContentProviderClient;
-import android.database.Cursor;
-import android.os.AsyncTask;
-import android.os.RemoteException;
-
-import java.util.Date;
-
-class CategoryCountUpdater extends AsyncTask<Void, Void, Void> {
-
-    private final String name;
-    private final ContentProviderClient client;
-
-    CategoryCountUpdater(String name, ContentProviderClient client) {
-        this.name = name;
-        this.client = client;
-    }
-
-    @Override
-    protected Void doInBackground(Void... voids) {
-        Category cat = lookupCategory(name);
-        cat.incTimesUsed();
-
-        cat.setContentProviderClient(client);
-        cat.save();
-
-        return null; // Make the compiler happy.
-    }
-
-    private Category lookupCategory(String name) {
-        Cursor cursor = null;
-        try {
-            cursor = client.query(
-                    CategoryContentProvider.BASE_URI,
-                    Category.Table.ALL_FIELDS,
-                    Category.Table.COLUMN_NAME + "=?",
-                    new String[]{name},
-                    null);
-            if (cursor != null && cursor.moveToFirst()) {
-                return Category.fromCursor(cursor);
-            }
-        } catch (RemoteException e) {
-            // This feels lazy, but to hell with checked exceptions. :)
-            throw new RuntimeException(e);
-        } finally {
-            if (cursor != null) {
-                cursor.close();
-            }
-        }
-
-        // Newly used category...
-        Category cat = new Category();
-        cat.setName(name);
-        cat.setLastUsed(new Date());
-        cat.setTimesUsed(0);
-        return cat;
-    }
-}

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

@@ -51,4 +51,24 @@ class CategoryItem implements Parcelable {
         parcel.writeString(name);
         parcel.writeInt(selected ? 1 : 0);
     }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        CategoryItem that = (CategoryItem) o;
+
+        return name.equals(that.name);
+
+    }
+
+    @Override
+    public int hashCode() {
+        return name.hashCode();
+    }
 }

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

@@ -1,100 +0,0 @@
-package fr.free.nrw.commons.category;
-
-import android.os.AsyncTask;
-import android.view.View;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Calendar;
-import java.util.Iterator;
-import java.util.List;
-
-import fr.free.nrw.commons.CommonsApplication;
-import fr.free.nrw.commons.mwapi.MediaWikiApi;
-import timber.log.Timber;
-
-import static fr.free.nrw.commons.category.CategorizationFragment.SEARCH_CATS_LIMIT;
-
-/**
- * Sends asynchronous queries to the Commons MediaWiki API to retrieve categories that are close to
- * the keyword typed in by the user. The 'srsearch' action-specific parameter is used for this
- * purpose. This class should be subclassed in CategorizationFragment.java to aggregate the results.
- */
-class MethodAUpdater extends AsyncTask<Void, Void, List<String>> {
-
-    private final CategorizationFragment catFragment;
-    private String filter;
-
-    MethodAUpdater(CategorizationFragment catFragment) {
-        this.catFragment = catFragment;
-    }
-
-    @Override
-    protected void onPreExecute() {
-        super.onPreExecute();
-        filter = catFragment.categoriesFilter.getText().toString();
-        catFragment.categoriesSearchInProgress.setVisibility(View.VISIBLE);
-        catFragment.categoriesNotFoundView.setVisibility(View.GONE);
-
-        catFragment.categoriesSkip.setVisibility(View.GONE);
-    }
-
-    /**
-     * Remove categories that contain a year in them (starting with 19__ or 20__), except for this year
-     * and previous year
-     * Rationale: https://github.com/commons-app/apps-android-commons/issues/47
-     *
-     * @param items Unfiltered list of categories
-     * @return Filtered category list
-     */
-    private List<String> filterYears(List<String> items) {
-
-        Iterator<String> iterator;
-
-        //Check for current and previous year to exclude these categories from removal
-        Calendar now = Calendar.getInstance();
-        int year = now.get(Calendar.YEAR);
-        String yearInString = String.valueOf(year);
-        Timber.d("Year: %s", yearInString);
-
-        int prevYear = year - 1;
-        String prevYearInString = String.valueOf(prevYear);
-        Timber.d("Previous year: %s", prevYearInString);
-
-        //Copy to Iterator to prevent ConcurrentModificationException when removing item
-        for (iterator = items.iterator(); iterator.hasNext(); ) {
-            String s = iterator.next();
-
-            //Check if s contains a 4-digit word anywhere within the string (.* is wildcard)
-            //And that s does not equal the current year or previous year
-            if (s.matches(".*(19|20)\\d{2}.*") && !s.contains(yearInString) && !s.contains(prevYearInString)) {
-                Timber.d("Filtering out year %s", s);
-                iterator.remove();
-            }
-        }
-
-        Timber.d("Items: %s", items);
-        return items;
-    }
-
-    @Override
-    protected List<String> doInBackground(Void... voids) {
-
-        //otherwise if user has typed something in that isn't in cache, search API for matching categories
-        MediaWikiApi api = CommonsApplication.getInstance().getMWApi();
-        List<String> categories = new ArrayList<>();
-
-        //URL https://commons.wikimedia.org/w/api.php?action=query&format=xml&list=search&srwhat=text&srenablerewrites=1&srnamespace=14&srlimit=10&srsearch=
-        try {
-            categories = api.searchCategories(SEARCH_CATS_LIMIT, filter);
-            Timber.d("Method A URL filter %s", categories);
-        } catch (IOException e) {
-            Timber.e(e, "IO Exception: ");
-            //Return empty arraylist
-            return categories;
-        }
-
-        Timber.d("Found categories from Method A search, waiting for filter");
-        return new ArrayList<>(filterYears(categories));
-    }
-}

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

@@ -1,7 +1,7 @@
 package fr.free.nrw.commons.category;
 
-import java.util.ArrayList;
+import java.util.List;
 
 public interface OnCategoriesSaveHandler {
-    void onCategoriesSave(ArrayList<String> categories);
+    void onCategoriesSave(List<String> categories);
 }

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

@@ -1,119 +0,0 @@
-package fr.free.nrw.commons.category;
-
-import android.os.AsyncTask;
-import android.text.TextUtils;
-import android.view.View;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Calendar;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.List;
-
-import fr.free.nrw.commons.CommonsApplication;
-import fr.free.nrw.commons.mwapi.MediaWikiApi;
-import timber.log.Timber;
-
-import static fr.free.nrw.commons.category.CategorizationFragment.SEARCH_CATS_LIMIT;
-
-/**
- * Sends asynchronous queries to the Commons MediaWiki API to retrieve categories that share the
- * same prefix as the keyword typed in by the user. The 'acprefix' action-specific parameter is used
- * for this purpose. This class should be subclassed in CategorizationFragment.java to aggregate
- * the results.
- */
-class PrefixUpdater extends AsyncTask<Void, Void, List<String>> {
-
-    private final CategorizationFragment catFragment;
-    private String filter;
-
-    PrefixUpdater(CategorizationFragment catFragment) {
-        this.catFragment = catFragment;
-    }
-
-    @Override
-    protected void onPreExecute() {
-        super.onPreExecute();
-        filter = catFragment.categoriesFilter.getText().toString();
-        catFragment.categoriesSearchInProgress.setVisibility(View.VISIBLE);
-        catFragment.categoriesNotFoundView.setVisibility(View.GONE);
-
-        catFragment.categoriesSkip.setVisibility(View.GONE);
-    }
-
-    /**
-     * Remove categories that contain a year in them (starting with 19__ or 20__), except for this year
-     * and previous year
-     * Rationale: https://github.com/commons-app/apps-android-commons/issues/47
-     *
-     * @param items Unfiltered list of categories
-     * @return Filtered category list
-     */
-    private List<String> filterIrrelevantResults(List<String> items) {
-
-        Iterator<String> iterator;
-
-        //Check for current and previous year to exclude these categories from removal
-        Calendar now = Calendar.getInstance();
-        int year = now.get(Calendar.YEAR);
-        String yearInString = String.valueOf(year);
-        Timber.d("Year: %s", yearInString);
-
-        int prevYear = year - 1;
-        String prevYearInString = String.valueOf(prevYear);
-        Timber.d("Previous year: %s", prevYearInString);
-
-        //Copy to Iterator to prevent ConcurrentModificationException when removing item
-        for (iterator = items.iterator(); iterator.hasNext();) {
-            String s = iterator.next();
-
-            //Check if s contains a 4-digit word anywhere within the string (.* is wildcard)
-            //And that s does not equal the current year or previous year
-            //And if it is an irrelevant category such as Media_needing_categories_as_of_16_June_2017(Issue #750)
-            if ((s.matches(".*(19|20)\\d{2}.*") && !s.contains(yearInString) && !s.contains(prevYearInString))
-                    || s.matches("(.*)needing(.*)")||s.matches("(.*)taken on(.*)")) {
-                Timber.d("Filtering out irrelevant result: %s", s);
-                iterator.remove();
-            }
-
-        }
-
-        Timber.d("Items: %s", items);
-        return items;
-    }
-
-    @Override
-    protected List<String> doInBackground(Void... voids) {
-        //If user hasn't typed anything in yet, get GPS and recent items
-        if (TextUtils.isEmpty(filter)) {
-            ArrayList<String> mergedItems = new ArrayList<>(catFragment.mergeItems());
-            Timber.d("Merged items, waiting for filter");
-            return new ArrayList<>(filterIrrelevantResults(mergedItems));
-        }
-
-        //if user types in something that is in cache, return cached category
-        HashMap<String, ArrayList<String>> categoriesCache = catFragment.getCategoriesCache();
-        if (categoriesCache.containsKey(filter)) {
-            ArrayList<String> cachedItems = new ArrayList<>(categoriesCache.get(filter));
-            Timber.d("Found cache items, waiting for filter");
-            return new ArrayList<>(filterIrrelevantResults(cachedItems));
-        }
-
-        //otherwise if user has typed something in that isn't in cache, search API for matching categories
-        //URL: https://commons.wikimedia.org/w/api.php?action=query&list=allcategories&acprefix=filter&aclimit=25
-        MediaWikiApi api = CommonsApplication.getInstance().getMWApi();
-        List<String> categories = new ArrayList<>();
-        try {
-            categories = api.allCategories(SEARCH_CATS_LIMIT, this.filter);
-            Timber.d("Prefix URL filter %s", categories);
-        } catch (IOException e) {
-            Timber.e(e, "IO Exception: ");
-            //Return empty arraylist
-            return categories;
-        }
-
-        Timber.d("Found categories from Prefix search, waiting for filter");
-        return new ArrayList<>(filterIrrelevantResults(categories));
-    }
-}

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

@@ -1,48 +0,0 @@
-package fr.free.nrw.commons.category;
-
-import android.os.AsyncTask;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
-
-import fr.free.nrw.commons.CommonsApplication;
-import fr.free.nrw.commons.mwapi.MediaWikiApi;
-import timber.log.Timber;
-
-/**
- * Sends asynchronous queries to the Commons MediaWiki API to retrieve categories that are related to
- * the title entered in previous screen. The 'srsearch' action-specific parameter is used for this
- * purpose. This class should be subclassed in CategorizationFragment.java to add the results to recent and GPS cats.
- */
-class TitleCategories extends AsyncTask<Void, Void, List<String>> {
-
-    private final static int SEARCH_CATS_LIMIT = 25;
-
-    private final String title;
-
-    TitleCategories(String title) {
-        this.title = title;
-    }
-
-    @Override
-    protected List<String> doInBackground(Void... voids) {
-
-        MediaWikiApi api = CommonsApplication.getInstance().getMWApi();
-        List<String> titleCategories = new ArrayList<>();
-
-        //URL https://commons.wikimedia.org/w/api.php?action=query&format=xml&list=search&srwhat=text&srenablerewrites=1&srnamespace=14&srlimit=10&srsearch=
-        try {
-            titleCategories = api.searchTitles(SEARCH_CATS_LIMIT, this.title);
-        } catch (IOException e) {
-            Timber.e(e, "IO Exception: ");
-            //Return empty arraylist
-            return titleCategories;
-        }
-
-        Timber.d("Title cat query results: %s", titleCategories);
-
-        return titleCategories;
-    }
-
-}

app/src/main/java/fr/free/nrw/commons/data/Category.java

@@ -1,4 +1,4 @@
-package fr.free.nrw.commons.category;
+package fr.free.nrw.commons.data;
 
 import android.content.ContentProviderClient;
 import android.content.ContentValues;
@@ -6,11 +6,15 @@ import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.net.Uri;
 import android.os.RemoteException;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
+import java.util.ArrayList;
 import java.util.Date;
 
+import fr.free.nrw.commons.category.CategoryContentProvider;
+
 public class Category {
-    private ContentProviderClient client;
     private Uri contentUri;
 
     private String name;
@@ -53,12 +57,13 @@ public class Category {
         touch();
     }
 
-    // Database/content-provider stuff
+    //region Database/content-provider stuff
-    public void setContentProviderClient(ContentProviderClient client) {
-        this.client = client;
-    }
 
-    public void save() {
+    /**
+     * Persist category.
+     * @param client ContentProviderClient to handle DB connection
+     */
+    public void save(ContentProviderClient client) {
         try {
             if (contentUri == null) {
                 contentUri = client.insert(CategoryContentProvider.BASE_URI, this.toContentValues());
@@ -78,7 +83,7 @@ public class Category {
         return cv;
     }
 
-    public static Category fromCursor(Cursor cursor) {
+    private static Category fromCursor(Cursor cursor) {
         // Hardcoding column positions!
         Category c = new Category();
         c.contentUri = CategoryContentProvider.uriForId(cursor.getInt(0));
@@ -88,6 +93,65 @@ public class Category {
         return c;
     }
 
+    /**
+     * Find persisted category in database, based on its name.
+     * @param client ContentProviderClient to handle DB connection
+     * @param name Category's name
+     * @return category from database, or null if not found
+     */
+    public static @Nullable Category find(ContentProviderClient client, String name) {
+        Cursor cursor = null;
+        try {
+            cursor = client.query(
+                    CategoryContentProvider.BASE_URI,
+                    Category.Table.ALL_FIELDS,
+                    Category.Table.COLUMN_NAME + "=?",
+                    new String[]{name},
+                    null);
+            if (cursor != null && cursor.moveToFirst()) {
+                return Category.fromCursor(cursor);
+            }
+        } catch (RemoteException e) {
+            // This feels lazy, but to hell with checked exceptions. :)
+            throw new RuntimeException(e);
+        } finally {
+            if (cursor != null) {
+                cursor.close();
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Retrieve recently-used categories, ordered by descending date.
+     * @return a list containing recent categories
+     */
+    public static @NonNull ArrayList<String> recentCategories(ContentProviderClient client, int limit) {
+        ArrayList<String> items = new ArrayList<>();
+        Cursor cursor = null;
+        try {
+            cursor = client.query(
+                    CategoryContentProvider.BASE_URI,
+                    Category.Table.ALL_FIELDS,
+                    null,
+                    new String[]{},
+                    Category.Table.COLUMN_LAST_USED + " DESC");
+            // fixme add a limit on the original query instead of falling out of the loop?
+            while (cursor != null && cursor.moveToNext()
+                    && cursor.getPosition() < limit) {
+                Category cat = Category.fromCursor(cursor);
+                items.add(cat.getName());
+            }
+        } catch (RemoteException e) {
+            throw new RuntimeException(e);
+        } finally {
+            if (cursor != null) {
+                cursor.close();
+            }
+        }
+        return items;
+    }
+
     public static class Table {
         public static final String TABLE_NAME = "categories";
 
@@ -144,4 +208,5 @@ public class Category {
             }
         }
     }
+    //endregion
 }

app/src/main/java/fr/free/nrw/commons/data/DBOpenHelper.java

@@ -4,7 +4,6 @@ import android.content.Context;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
 
-import fr.free.nrw.commons.category.Category;
 import fr.free.nrw.commons.contributions.Contribution;
 import fr.free.nrw.commons.modifications.ModifierSequence;
 

app/src/main/java/fr/free/nrw/commons/mwapi/ApacheHttpClientMediaWikiApi.java

@@ -35,6 +35,7 @@ import fr.free.nrw.commons.BuildConfig;
 import fr.free.nrw.commons.PageTitle;
 import fr.free.nrw.commons.Utils;
 import in.yuvi.http.fluent.Http;
+import io.reactivex.Observable;
 import io.reactivex.Single;
 import timber.log.Timber;
 
@@ -205,78 +206,104 @@ public class ApacheHttpClientMediaWikiApi implements MediaWikiApi {
 
     @Override
     @NonNull
-    public List<String> searchCategories(int searchCatsLimit, String filterValue) throws IOException {
+    public Observable<String> searchCategories(String filterValue, int searchCatsLimit) {
-        List<ApiResult> categoryNodes = api.action("query")
+        return Single.fromCallable(() -> {
-                .param("format", "xml")
+            List<ApiResult> categoryNodes = null;
-                .param("list", "search")
+            try {
-                .param("srwhat", "text")
+                categoryNodes = api.action("query")
-                .param("srnamespace", "14")
+                        .param("format", "xml")
-                .param("srlimit", searchCatsLimit)
+                        .param("list", "search")
-                .param("srsearch", filterValue)
+                        .param("srwhat", "text")
-                .get()
+                        .param("srnamespace", "14")
-                .getNodes("/api/query/search/p/@title");
+                        .param("srlimit", searchCatsLimit)
+                        .param("srsearch", filterValue)
+                        .get()
+                        .getNodes("/api/query/search/p/@title");
+            } catch (IOException e) {
+                Timber.e("Failed to obtain searchCategories", e);
+            }
 
-        if (categoryNodes == null) {
+            if (categoryNodes == null) {
-            return Collections.emptyList();
+                return new ArrayList<String>();
-        }
+            }
 
-        List<String> categories = new ArrayList<>();
+            List<String> categories = new ArrayList<>();
-        for (ApiResult categoryNode : categoryNodes) {
+            for (ApiResult categoryNode : categoryNodes) {
-            String cat = categoryNode.getDocument().getTextContent();
+                String cat = categoryNode.getDocument().getTextContent();
-            String catString = cat.replace("Category:", "");
+                String catString = cat.replace("Category:", "");
-            categories.add(catString);
+                categories.add(catString);
-        }
+            }
 
-        return categories;
+            return categories;
+        })
+                .flatMapObservable(list -> Observable.fromIterable(list));
     }
 
     @Override
     @NonNull
-    public List<String> allCategories(int searchCatsLimit, String filterValue) throws IOException {
+    public Observable<String> allCategories(String filterValue, int searchCatsLimit) {
-        ArrayList<ApiResult> categoryNodes = api.action("query")
+        return Single.fromCallable(() -> {
-                .param("list", "allcategories")
+            ArrayList<ApiResult> categoryNodes = null;
-                .param("acprefix", filterValue)
+            try {
-                .param("aclimit", searchCatsLimit)
+                categoryNodes = api.action("query")
-                .get()
+                        .param("list", "allcategories")
-                .getNodes("/api/query/allcategories/c");
+                        .param("acprefix", filterValue)
+                        .param("aclimit", searchCatsLimit)
+                        .get()
+                        .getNodes("/api/query/allcategories/c");
+            } catch (IOException e) {
+                Timber.e("Failed to obtain allCategories", e);
+            }
 
-        if (categoryNodes == null) {
+            if (categoryNodes == null) {
-            return Collections.emptyList();
+                return new ArrayList<String>();
-        }
+            }
 
-        List<String> categories = new ArrayList<>();
+            List<String> categories = new ArrayList<>();
-        for (ApiResult categoryNode : categoryNodes) {
+            for (ApiResult categoryNode : categoryNodes) {
-            categories.add(categoryNode.getDocument().getTextContent());
+                categories.add(categoryNode.getDocument().getTextContent());
-        }
+            }
 
-        return categories;
+            return categories;
+        })
+                .flatMapObservable(list -> Observable.fromIterable(list));
     }
 
     @Override
     @NonNull
-    public List<String> searchTitles(int searchCatsLimit, String title) throws IOException {
+    public Observable<String> searchTitles(String title, int searchCatsLimit) {
-        ArrayList<ApiResult> categoryNodes = api.action("query")
+        return Single.fromCallable(() -> {
-                .param("format", "xml")
+            ArrayList<ApiResult> categoryNodes = null;
-                .param("list", "search")
-                .param("srwhat", "text")
-                .param("srnamespace", "14")
-                .param("srlimit", searchCatsLimit)
-                .param("srsearch", title)
-                .get()
-                .getNodes("/api/query/search/p/@title");
 
-        if (categoryNodes == null) {
+            try {
-            return Collections.emptyList();
+                categoryNodes = api.action("query")
-        }
+                        .param("format", "xml")
+                        .param("list", "search")
+                        .param("srwhat", "text")
+                        .param("srnamespace", "14")
+                        .param("srlimit", searchCatsLimit)
+                        .param("srsearch", title)
+                        .get()
+                        .getNodes("/api/query/search/p/@title");
+            } catch (IOException e) {
+                Timber.e("Failed to obtain searchTitles", e);
+                return new ArrayList();
+            }
 
-        List<String> titleCategories = new ArrayList<>();
+            if (categoryNodes == null) {
-        for (ApiResult categoryNode : categoryNodes) {
+                return Collections.emptyList();
-            String cat = categoryNode.getDocument().getTextContent();
+            }
-            String catString = cat.replace("Category:", "");
-            titleCategories.add(catString);
-        }
 
-        return titleCategories;
+            List<String> titleCategories = new ArrayList<>();
+            for (ApiResult categoryNode : categoryNodes) {
+                String cat = categoryNode.getDocument().getTextContent();
+                String catString = cat.replace("Category:", "");
+                titleCategories.add(catString);
+            }
+
+            return titleCategories;
+        })
+                .flatMapObservable(list -> Observable.fromIterable(list));
     }
 
     @Override

app/src/main/java/fr/free/nrw/commons/mwapi/MediaWikiApi.java

@@ -7,6 +7,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;
 
+import io.reactivex.Observable;
 import io.reactivex.Single;
 
 public interface MediaWikiApi {
@@ -38,13 +39,13 @@ public interface MediaWikiApi {
     MediaResult fetchMediaByFilename(String filename) throws IOException;
 
     @NonNull
-    List<String> searchCategories(int searchCatsLimit, String filterValue) throws IOException;
+    Observable<String> searchCategories(String filterValue, int searchCatsLimit);
 
     @NonNull
-    List<String> allCategories(int searchCatsLimit, String filter) throws IOException;
+    Observable<String> allCategories(String filter, int searchCatsLimit);
 
     @NonNull
-    List<String> searchTitles(int searchCatsLimit, String title) throws IOException;
+    Observable<String> searchTitles(String title, int searchCatsLimit);
 
     @Nullable
     String revisionsByFilename(String filename) throws IOException;

app/src/main/java/fr/free/nrw/commons/upload/MultipleShareActivity.java

@@ -22,6 +22,7 @@ import android.widget.AdapterView;
 import android.widget.Toast;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import butterknife.ButterKnife;
 import fr.free.nrw.commons.CommonsApplication;
@@ -160,7 +161,7 @@ public  class       MultipleShareActivity
     }
 
     @Override
-    public void onCategoriesSave(ArrayList<String> categories) {
+    public void onCategoriesSave(List<String> categories) {
         if(categories.size() > 0) {
         ContentProviderClient client = getContentResolver().acquireContentProviderClient(ModificationsContentProvider.AUTHORITY);
             for(Contribution contribution: photosList) {

app/src/main/java/fr/free/nrw/commons/upload/ShareActivity.java

@@ -154,7 +154,7 @@ public  class       ShareActivity
     }
 
     @Override
-    public void onCategoriesSave(ArrayList<String> categories) {
+    public void onCategoriesSave(List<String> categories) {
         if(categories.size() > 0) {
             ModifierSequence categoriesSequence = new ModifierSequence(contribution.getContentUri());
 
@@ -525,7 +525,7 @@ public  class       ShareActivity
         switch (item.getItemId()) {
             case android.R.id.home:
                 if(categorizationFragment!=null && categorizationFragment.isVisible()) {
-                    categorizationFragment.backButtonDialog();
+                    categorizationFragment.showBackButtonDialog();
                 } else {
                     onBackPressed();
                 }

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

@@ -24,6 +24,7 @@
             android:layout_width="match_parent"
             android:hint="@string/categories_search_text_hint"
             android:maxLines="1"
+            android:inputType="text"
             android:imeOptions="flagNoExtractUi"
             />