convert top level classes to kotlin (#6368)

* Converted welcome activity / pager to kotlin

* Removed unused interface

* Convert ViewPagerAdapter to kotlin and enforce that all tabs must have a title that comes from strings.xml

* Convert OkHttpConnectionFactory and remove an exception class nobody was using

* Convert MapController to kotlin along with fixing nullability in a few places

.idea/codeStyles/Project.xml

@@ -16,6 +16,7 @@
       <option name="NAMES_COUNT_TO_USE_IMPORT_ON_DEMAND" value="999" />
       <option name="IMPORT_LAYOUT_TABLE">
         <value>
+          <package name="" withSubpackages="true" static="false" module="true" />
           <package name="" withSubpackages="true" static="true" />
           <emptyLine />
           <package name="" withSubpackages="true" static="false" />

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

@@ -1,30 +0,0 @@
-package fr.free.nrw.commons;
-
-import fr.free.nrw.commons.location.LatLng;
-import fr.free.nrw.commons.nearby.Place;
-import java.util.List;
-
-public abstract class MapController {
-
-    /**
-     * We pass this variable as a group of placeList and boundaryCoordinates
-     */
-    public class NearbyPlacesInfo {
-        public List<Place> placeList; // List of nearby places
-        public LatLng[] boundaryCoordinates; // Corners of nearby area
-        public LatLng currentLatLng; // Current location when this places are populated
-        public LatLng searchLatLng; // Search location for finding this places
-        public List<Media> mediaList; // Search location for finding this places
-    }
-
-    /**
-     * We pass this variable as a group of placeList and boundaryCoordinates
-     */
-    public class ExplorePlacesInfo {
-        public List<Place> explorePlaceList; // List of nearby places
-        public LatLng[] boundaryCoordinates; // Corners of nearby area
-        public LatLng currentLatLng; // Current location when this places are populated
-        public LatLng searchLatLng; // Search location for finding this places
-        public List<Media> mediaList; // Search location for finding this places
-    }
-}

app/src/main/java/fr/free/nrw/commons/MapController.kt

@@ -0,0 +1,46 @@
+package fr.free.nrw.commons
+
+import fr.free.nrw.commons.location.LatLng
+import fr.free.nrw.commons.nearby.Place
+
+abstract class MapController {
+    /**
+     * We pass this variable as a group of placeList and boundaryCoordinates
+     */
+    inner class NearbyPlacesInfo {
+        @JvmField
+        var placeList: List<Place> = emptyList() // List of nearby places
+
+        @JvmField
+        var boundaryCoordinates: Array<LatLng> = emptyArray() // Corners of nearby area
+
+        @JvmField
+        var currentLatLng: LatLng? = null // Current location when this places are populated
+
+        @JvmField
+        var searchLatLng: LatLng? = null // Search location for finding this places
+
+        @JvmField
+        var mediaList: List<Media>? = null // Search location for finding this places
+    }
+
+    /**
+     * We pass this variable as a group of placeList and boundaryCoordinates
+     */
+    inner class ExplorePlacesInfo {
+        @JvmField
+        var explorePlaceList: List<Place> = emptyList() // List of nearby places
+
+        @JvmField
+        var boundaryCoordinates: Array<LatLng> = emptyArray() // Corners of nearby area
+
+        @JvmField
+        var currentLatLng: LatLng? = null // Current location when this places are populated
+
+        @JvmField
+        var searchLatLng: LatLng? = null // Search location for finding this places
+
+        @JvmField
+        var mediaList: List<Media> = emptyList() // Search location for finding this places
+    }
+}

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

@@ -1,154 +0,0 @@
-package fr.free.nrw.commons;
-
-import androidx.annotation.NonNull;
-import fr.free.nrw.commons.wikidata.cookies.CommonsCookieJar;
-import java.io.File;
-import java.io.IOException;
-import java.util.Collections;
-import java.util.List;
-import java.util.concurrent.TimeUnit;
-import okhttp3.Cache;
-import okhttp3.Interceptor;
-import okhttp3.OkHttpClient;
-import okhttp3.Request;
-import okhttp3.Response;
-import okhttp3.ResponseBody;
-import okhttp3.logging.HttpLoggingInterceptor;
-import okhttp3.logging.HttpLoggingInterceptor.Level;
-import timber.log.Timber;
-
-public final class OkHttpConnectionFactory {
-    private static final String CACHE_DIR_NAME = "okhttp-cache";
-    private static final long NET_CACHE_SIZE = 64 * 1024 * 1024;
-
-    public static OkHttpClient CLIENT;
-
-    @NonNull public static OkHttpClient getClient(final CommonsCookieJar cookieJar) {
-        if (CLIENT == null) {
-            CLIENT = createClient(cookieJar);
-        }
-        return CLIENT;
-    }
-
-    @NonNull
-    private static OkHttpClient createClient(final CommonsCookieJar cookieJar) {
-        return new OkHttpClient.Builder()
-                .cookieJar(cookieJar)
-                .cache((CommonsApplication.getInstance()!=null) ? new Cache(new File(CommonsApplication.getInstance().getCacheDir(), CACHE_DIR_NAME), NET_CACHE_SIZE) : null)
-                .connectTimeout(120, TimeUnit.SECONDS)
-                .writeTimeout(120, TimeUnit.SECONDS)
-                .readTimeout(120, TimeUnit.SECONDS)
-                .addInterceptor(getLoggingInterceptor())
-                .addInterceptor(new UnsuccessfulResponseInterceptor())
-                .addInterceptor(new CommonHeaderRequestInterceptor())
-                .build();
-    }
-
-    private static HttpLoggingInterceptor getLoggingInterceptor() {
-        final HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor()
-            .setLevel(Level.BASIC);
-
-        httpLoggingInterceptor.redactHeader("Authorization");
-        httpLoggingInterceptor.redactHeader("Cookie");
-
-        return httpLoggingInterceptor;
-    }
-
-    private static class CommonHeaderRequestInterceptor implements Interceptor {
-
-        @Override
-        @NonNull
-        public Response intercept(@NonNull final Chain chain) throws IOException {
-            final Request request = chain.request().newBuilder()
-                    .header("User-Agent", CommonsApplication.getInstance().getUserAgent())
-                    .build();
-            return chain.proceed(request);
-        }
-    }
-
-    public static class UnsuccessfulResponseInterceptor implements Interceptor {
-        private static final String SUPPRESS_ERROR_LOG = "x-commons-suppress-error-log";
-        public static final String SUPPRESS_ERROR_LOG_HEADER = SUPPRESS_ERROR_LOG+": true";
-        private static final List<String> DO_NOT_INTERCEPT = Collections.singletonList(
-            "api.php?format=json&formatversion=2&errorformat=plaintext&action=upload&ignorewarnings=1");
-
-        private static final String ERRORS_PREFIX = "{\"error";
-
-        @Override
-        @NonNull
-        public Response intercept(@NonNull final Chain chain) throws IOException {
-            final Request rq = chain.request();
-
-            // If the request contains our special "suppress errors" header, make note of it
-            // but don't pass that on to the server.
-            final boolean suppressErrors = rq.headers().names().contains(SUPPRESS_ERROR_LOG);
-            final Request request = rq.newBuilder()
-                .removeHeader(SUPPRESS_ERROR_LOG)
-                .build();
-
-            final Response rsp = chain.proceed(request);
-
-            // Do not intercept certain requests and let the caller handle the errors
-            if(isExcludedUrl(chain.request())) {
-                return rsp;
-            }
-            if (rsp.isSuccessful()) {
-                try (final ResponseBody responseBody = rsp.peekBody(ERRORS_PREFIX.length())) {
-                    if (ERRORS_PREFIX.equals(responseBody.string())) {
-                        try (final ResponseBody body = rsp.body()) {
-                            throw new IOException(body.string());
-                        }
-                    }
-                } catch (final IOException e) {
-                    // Log the error as debug (and therefore, "expected") or at error level
-                    if (suppressErrors) {
-                        Timber.d(e, "Suppressed (known / expected) error");
-                    } else {
-                        Timber.e(e);
-                    }
-                }
-                return rsp;
-            }
-            throw new HttpStatusException(rsp);
-        }
-
-        private boolean isExcludedUrl(final Request request) {
-            final String requestUrl = request.url().toString();
-            for(final String url: DO_NOT_INTERCEPT) {
-                if(requestUrl.contains(url)) {
-                    return true;
-                }
-            }
-            return false;
-        }
-    }
-
-    private OkHttpConnectionFactory() {
-    }
-
-    public static class HttpStatusException extends IOException {
-        private final int code;
-        private final String url;
-        public HttpStatusException(@NonNull Response rsp) {
-            this.code = rsp.code();
-            this.url = rsp.request().url().uri().toString();
-            try {
-                if (rsp.body() != null && rsp.body().contentType() != null
-                        && rsp.body().contentType().toString().contains("json")) {
-                }
-            } catch (Exception e) {
-                // Log?
-            }
-        }
-
-        public int code() {
-            return code;
-        }
-
-        @Override
-        public String getMessage() {
-            String str = "Code: " + code + ", URL: " + url;
-            return str;
-        }
-    }
-}

app/src/main/java/fr/free/nrw/commons/OkHttpConnectionFactory.kt

@@ -0,0 +1,122 @@
+package fr.free.nrw.commons
+
+import androidx.annotation.VisibleForTesting
+import fr.free.nrw.commons.wikidata.cookies.CommonsCookieJar
+import okhttp3.Cache
+import okhttp3.Interceptor
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.Response
+import okhttp3.logging.HttpLoggingInterceptor
+import timber.log.Timber
+import java.io.File
+import java.io.IOException
+import java.util.concurrent.TimeUnit
+
+object OkHttpConnectionFactory {
+    private const val CACHE_DIR_NAME = "okhttp-cache"
+    private const val NET_CACHE_SIZE = (64 * 1024 * 1024).toLong()
+
+    @VisibleForTesting
+    var CLIENT: OkHttpClient? = null
+
+    fun getClient(cookieJar: CommonsCookieJar): OkHttpClient {
+        if (CLIENT == null) {
+            CLIENT = createClient(cookieJar)
+        }
+        return CLIENT!!
+    }
+
+    private fun createClient(cookieJar: CommonsCookieJar): OkHttpClient {
+        return OkHttpClient.Builder()
+            .cookieJar(cookieJar)
+            .cache(
+                if (CommonsApplication.instance != null) Cache(
+                    File(CommonsApplication.instance.cacheDir, CACHE_DIR_NAME),
+                    NET_CACHE_SIZE
+                ) else null
+            )
+            .connectTimeout(120, TimeUnit.SECONDS)
+            .writeTimeout(120, TimeUnit.SECONDS)
+            .readTimeout(120, TimeUnit.SECONDS)
+            .addInterceptor(HttpLoggingInterceptor().apply {
+                setLevel(HttpLoggingInterceptor.Level.BASIC)
+                redactHeader("Authorization")
+                redactHeader("Cookie")
+            })
+            .addInterceptor(UnsuccessfulResponseInterceptor())
+            .addInterceptor(CommonHeaderRequestInterceptor())
+            .build()
+    }
+}
+
+private class CommonHeaderRequestInterceptor : Interceptor {
+    @Throws(IOException::class)
+    override fun intercept(chain: Interceptor.Chain): Response {
+        val request = chain.request().newBuilder()
+            .header("User-Agent", CommonsApplication.instance.userAgent)
+            .build()
+        return chain.proceed(request)
+    }
+}
+
+private const val SUPPRESS_ERROR_LOG = "x-commons-suppress-error-log"
+const val SUPPRESS_ERROR_LOG_HEADER: String = "$SUPPRESS_ERROR_LOG: true"
+
+private class UnsuccessfulResponseInterceptor : Interceptor {
+    @Throws(IOException::class)
+    override fun intercept(chain: Interceptor.Chain): Response {
+        val rq = chain.request()
+
+        // If the request contains our special "suppress errors" header, make note of it
+        // but don't pass that on to the server.
+        val suppressErrors = rq.headers.names().contains(SUPPRESS_ERROR_LOG)
+        val request = rq.newBuilder()
+            .removeHeader(SUPPRESS_ERROR_LOG)
+            .build()
+
+        val rsp = chain.proceed(request)
+
+        // Do not intercept certain requests and let the caller handle the errors
+        if (isExcludedUrl(chain.request())) {
+            return rsp
+        }
+        if (rsp.isSuccessful) {
+            try {
+                rsp.peekBody(ERRORS_PREFIX.length.toLong()).use { responseBody ->
+                    if (ERRORS_PREFIX == responseBody.string()) {
+                        rsp.body.use { body ->
+                            throw IOException(body!!.string())
+                        }
+                    }
+                }
+            } catch (e: IOException) {
+                // Log the error as debug (and therefore, "expected") or at error level
+                if (suppressErrors) {
+                    Timber.d(e, "Suppressed (known / expected) error")
+                } else {
+                    Timber.e(e)
+                }
+            }
+            return rsp
+        }
+        throw IOException("Unsuccessful response")
+    }
+
+    private fun isExcludedUrl(request: Request): Boolean {
+        val requestUrl = request.url.toString()
+        for (url in DO_NOT_INTERCEPT) {
+            if (requestUrl.contains(url)) {
+                return true
+            }
+        }
+        return false
+    }
+
+    companion object {
+        val DO_NOT_INTERCEPT = listOf(
+            "api.php?format=json&formatversion=2&errorformat=plaintext&action=upload&ignorewarnings=1"
+        )
+        const val ERRORS_PREFIX = "{\"error"
+    }
+}

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

@@ -1,7 +0,0 @@
-package fr.free.nrw.commons;
-
-import android.content.Context;
-
-public interface ViewHolder<T> {
-    void bindModel(Context context, T model);
-}

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

@@ -1,68 +0,0 @@
-package fr.free.nrw.commons;
-
-import androidx.fragment.app.Fragment;
-import androidx.fragment.app.FragmentManager;
-import androidx.fragment.app.FragmentPagerAdapter;
-
-import java.util.ArrayList;
-import java.util.List;
-
-/**
- * This adapter will be used to display fragments in a ViewPager
- */
-public class ViewPagerAdapter extends FragmentPagerAdapter {
-    private List<Fragment> fragmentList = new ArrayList<>();
-    private List<String> fragmentTitleList = new ArrayList<>();
-
-    public ViewPagerAdapter(FragmentManager manager) {
-        super(manager);
-    }
-
-    /**
-     * Constructs a ViewPagerAdapter with a specified Fragment Manager and Fragment resume behavior.
-     *
-     * @param manager The FragmentManager
-     * @param behavior An integer which represents the behavior of non visible fragments. See
-     *                 FragmentPagerAdapter.java for options.
-     */
-    public ViewPagerAdapter(FragmentManager manager, int behavior) {
-        super(manager, behavior);
-    }
-
-    /**
-     * This method returns the fragment of the viewpager at a particular position
-     * @param position
-     */
-    @Override
-    public Fragment getItem(int position) {
-        return fragmentList.get(position);
-    }
-
-    /**
-     * This method returns the total number of fragments in the viewpager.
-     * @return size
-     */
-    @Override
-    public int getCount() {
-        return fragmentList.size();
-    }
-
-    /**
-     * This method sets the fragment and title list in the viewpager
-     * @param fragmentList List of all fragments to be displayed in the viewpager
-     * @param fragmentTitleList List of all titles of the fragments
-     */
-    public void setTabData(List<Fragment> fragmentList, List<String> fragmentTitleList) {
-        this.fragmentList = fragmentList;
-        this.fragmentTitleList = fragmentTitleList;
-    }
-
-    /**
-     * This method returns the title of the page at a particular position
-     * @param position
-     */
-    @Override
-    public CharSequence getPageTitle(int position) {
-        return fragmentTitleList.get(position);
-    }
-}

app/src/main/java/fr/free/nrw/commons/ViewPagerAdapter.kt

@@ -0,0 +1,44 @@
+package fr.free.nrw.commons
+
+import android.content.Context
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.FragmentManager
+import androidx.fragment.app.FragmentPagerAdapter
+import java.util.Locale
+
+/**
+ * This adapter will be used to display fragments in a ViewPager
+ */
+class ViewPagerAdapter : FragmentPagerAdapter {
+    private val context: Context
+    private var fragmentList: List<Fragment> = emptyList()
+    private var fragmentTitleList: List<String> = emptyList()
+
+    constructor(context: Context, manager: FragmentManager) : super(manager) {
+        this.context = context
+    }
+
+    constructor(context: Context, manager: FragmentManager, behavior: Int) : super(manager, behavior) {
+        this.context = context
+    }
+
+    override fun getItem(position: Int): Fragment = fragmentList[position]
+
+    override fun getPageTitle(position: Int): CharSequence = fragmentTitleList[position]
+
+    override fun getCount(): Int = fragmentList.size
+
+    fun setTabs(vararg titlesToFragments: Pair<Int, Fragment>) {
+        // Enforce that every title must come from strings.xml and all will consistently be uppercase
+        fragmentTitleList = titlesToFragments.map {
+            context.getString(it.first).uppercase(Locale.ROOT)
+        }
+        fragmentList = titlesToFragments.map { it.second }
+    }
+
+    companion object {
+        // Convenience method for Java callers, can be removed when everything is migrated
+        @JvmStatic
+        fun pairOf(first: Int, second: Fragment) = first to second
+    }
+}

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

@@ -1,109 +0,0 @@
-package fr.free.nrw.commons;
-
-import android.app.AlertDialog;
-import android.content.Context;
-import android.content.Intent;
-import android.os.Bundle;
-import android.view.View;
-import fr.free.nrw.commons.databinding.ActivityWelcomeBinding;
-import fr.free.nrw.commons.databinding.PopupForCopyrightBinding;
-import fr.free.nrw.commons.quiz.QuizActivity;
-import fr.free.nrw.commons.theme.BaseActivity;
-import fr.free.nrw.commons.utils.ConfigUtils;
-
-public class WelcomeActivity extends BaseActivity {
-
-    private ActivityWelcomeBinding binding;
-    private PopupForCopyrightBinding copyrightBinding;
-
-    private final WelcomePagerAdapter adapter = new WelcomePagerAdapter();
-    private boolean isQuiz;
-    private AlertDialog.Builder dialogBuilder;
-    private AlertDialog dialog;
-
-    /**
-     * Initialises exiting fields and dependencies
-     *
-     * @param savedInstanceState WelcomeActivity bundled data
-     */
-    @Override
-    public void onCreate(final Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-        binding = ActivityWelcomeBinding.inflate(getLayoutInflater());
-        final View view = binding.getRoot();
-        setContentView(view);
-
-        if (getIntent() != null) {
-            final Bundle bundle = getIntent().getExtras();
-            if (bundle != null) {
-                isQuiz = bundle.getBoolean("isQuiz");
-            }
-        } else {
-            isQuiz = false;
-        }
-
-        // Enable skip button if beta flavor
-        if (ConfigUtils.isBetaFlavour()) {
-            binding.finishTutorialButton.setVisibility(View.VISIBLE);
-
-            dialogBuilder = new AlertDialog.Builder(this);
-            copyrightBinding = PopupForCopyrightBinding.inflate(getLayoutInflater());
-            final View contactPopupView = copyrightBinding.getRoot();
-            dialogBuilder.setView(contactPopupView);
-            dialogBuilder.setCancelable(false);
-            dialog = dialogBuilder.create();
-            dialog.show();
-
-            copyrightBinding.buttonOk.setOnClickListener(v -> dialog.dismiss());
-        }
-
-        binding.welcomePager.setAdapter(adapter);
-        binding.welcomePagerIndicator.setViewPager(binding.welcomePager);
-
-        binding.finishTutorialButton.setOnClickListener(v -> finishTutorial());
-
-    }
-
-    /**
-     * References WelcomePageAdapter to null before the activity is destroyed
-     */
-    @Override
-    public void onDestroy() {
-        if (isQuiz) {
-            final Intent i = new Intent(this, QuizActivity.class);
-            startActivity(i);
-        }
-        super.onDestroy();
-    }
-
-    /**
-     * Creates a way to change current activity to WelcomeActivity
-     *
-     * @param context Activity context
-     */
-    public static void startYourself(final Context context) {
-        final Intent welcomeIntent = new Intent(context, WelcomeActivity.class);
-        context.startActivity(welcomeIntent);
-    }
-
-    /**
-     * Override onBackPressed() to go to previous tutorial 'pages' if not on first page
-     */
-    @Override
-    public void onBackPressed() {
-        if (binding.welcomePager.getCurrentItem() != 0) {
-            binding.welcomePager.setCurrentItem(binding.welcomePager.getCurrentItem() - 1, true);
-        } else {
-            if (defaultKvStore.getBoolean("firstrun", true)) {
-                finishAffinity();
-            } else {
-                super.onBackPressed();
-            }
-        }
-    }
-
-    public void finishTutorial() {
-        defaultKvStore.putBoolean("firstrun", false);
-        finish();
-    }
-}

app/src/main/java/fr/free/nrw/commons/WelcomeActivity.kt

@@ -0,0 +1,78 @@
+package fr.free.nrw.commons
+
+import android.app.AlertDialog
+import android.content.Context
+import android.content.Intent
+import android.os.Bundle
+import android.view.View
+import fr.free.nrw.commons.databinding.ActivityWelcomeBinding
+import fr.free.nrw.commons.databinding.PopupForCopyrightBinding
+import fr.free.nrw.commons.quiz.QuizActivity
+import fr.free.nrw.commons.theme.BaseActivity
+import fr.free.nrw.commons.utils.ConfigUtils.isBetaFlavour
+
+class WelcomeActivity : BaseActivity() {
+    private var binding: ActivityWelcomeBinding? = null
+    private var isQuiz = false
+
+    /**
+     * Initialises exiting fields and dependencies
+     *
+     * @param savedInstanceState WelcomeActivity bundled data
+     */
+    public override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        binding = ActivityWelcomeBinding.inflate(layoutInflater)
+        setContentView(binding!!.root)
+
+        isQuiz = intent?.extras?.getBoolean("isQuiz", false) ?: false
+
+        // Enable skip button if beta flavor
+        if (isBetaFlavour) {
+            binding!!.finishTutorialButton.visibility = View.VISIBLE
+
+            val copyrightBinding = PopupForCopyrightBinding.inflate(layoutInflater)
+
+            val dialog = AlertDialog.Builder(this)
+                .setView(copyrightBinding.root)
+                .setCancelable(false)
+                .create()
+            dialog.show()
+
+            copyrightBinding.buttonOk.setOnClickListener { v: View? -> dialog.dismiss() }
+        }
+
+        val adapter = WelcomePagerAdapter()
+        binding!!.welcomePager.adapter = adapter
+        binding!!.welcomePagerIndicator.setViewPager(binding!!.welcomePager)
+        binding!!.finishTutorialButton.setOnClickListener { v: View? -> finishTutorial() }
+    }
+
+    public override fun onDestroy() {
+        if (isQuiz) {
+            startActivity(Intent(this, QuizActivity::class.java))
+        }
+        super.onDestroy()
+    }
+
+    override fun onBackPressed() {
+        if (binding!!.welcomePager.currentItem != 0) {
+            binding!!.welcomePager.setCurrentItem(binding!!.welcomePager.currentItem - 1, true)
+        } else {
+            if (defaultKvStore.getBoolean("firstrun", true)) {
+                finishAffinity()
+            } else {
+                super.onBackPressed()
+            }
+        }
+    }
+
+    fun finishTutorial() {
+        defaultKvStore.putBoolean("firstrun", false)
+        finish()
+    }
+}
+
+fun Context.startWelcome() {
+    startActivity(Intent(this, WelcomeActivity::class.java))
+}

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

@@ -1,77 +0,0 @@
-package fr.free.nrw.commons;
-
-import static fr.free.nrw.commons.utils.UrlUtilsKt.handleWebUrl;
-
-import android.net.Uri;
-import android.view.LayoutInflater;
-import android.view.View;
-import android.view.ViewGroup;
-import android.widget.TextView;
-
-import androidx.viewpager.widget.PagerAdapter;
-import fr.free.nrw.commons.utils.UnderlineUtils;
-
-public class WelcomePagerAdapter extends PagerAdapter {
-    private static final int[] PAGE_LAYOUTS = new int[]{
-            R.layout.welcome_wikipedia,
-            R.layout.welcome_do_upload,
-            R.layout.welcome_dont_upload,
-            R.layout.welcome_image_example,
-            R.layout.welcome_final
-    };
-
-    /**
-     * Gets total number of layouts
-     * @return Number of layouts
-     */
-    @Override
-    public int getCount() {
-        return PAGE_LAYOUTS.length;
-    }
-
-    /**
-     * Compares given view with provided object
-     * @param view Adapter view
-     * @param object Adapter object
-     * @return Equality between view and object
-     */
-    @Override
-    public boolean isViewFromObject(View view, Object object) {
-        return (view == object);
-    }
-
-    @Override
-    public Object instantiateItem(ViewGroup container, int position) {
-        LayoutInflater inflater = LayoutInflater.from(container.getContext());
-        ViewGroup layout = (ViewGroup) inflater.inflate(PAGE_LAYOUTS[position], container, false);
-
-        // If final page
-        if (position == PAGE_LAYOUTS.length - 1) {
-            // Add link to more information
-            TextView moreInfo = layout.findViewById(R.id.welcomeInfo);
-            UnderlineUtils.setUnderlinedText(moreInfo, R.string.welcome_help_button_text);
-            moreInfo.setOnClickListener(view -> handleWebUrl(
-                    container.getContext(),
-                    Uri.parse("https://commons.wikimedia.org/wiki/Help:Contents")
-            ));
-
-            // Handle click of finishTutorialButton ("YES!" button) inside layout
-            layout.findViewById(R.id.finishTutorialButton)
-                    .setOnClickListener(view -> ((WelcomeActivity) container.getContext()).finishTutorial());
-        }
-
-        container.addView(layout);
-        return layout;
-    }
-
-    /**
-     * Provides a way to remove an item from container
-     * @param container Adapter view group container
-     * @param position Index of item
-     * @param obj Adapter object
-     */
-    @Override
-    public void destroyItem(ViewGroup container, int position, Object obj) {
-        container.removeView((View) obj);
-    }
-}

app/src/main/java/fr/free/nrw/commons/WelcomePagerAdapter.kt

@@ -0,0 +1,70 @@
+package fr.free.nrw.commons
+
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.TextView
+import androidx.core.net.toUri
+import androidx.viewpager.widget.PagerAdapter
+import fr.free.nrw.commons.utils.UnderlineUtils.setUnderlinedText
+import fr.free.nrw.commons.utils.handleWebUrl
+
+class WelcomePagerAdapter : PagerAdapter() {
+    /**
+     * Gets total number of layouts
+     * @return Number of layouts
+     */
+    override fun getCount(): Int = PAGE_LAYOUTS.size
+
+    /**
+     * Compares given view with provided object
+     * @param view Adapter view
+     * @param obj Adapter object
+     * @return Equality between view and object
+     */
+    override fun isViewFromObject(view: View, obj: Any): Boolean = (view === obj)
+
+    /**
+     * Provides a way to remove an item from container
+     * @param container Adapter view group container
+     * @param position Index of item
+     * @param obj Adapter object
+     */
+    override fun destroyItem(container: ViewGroup, position: Int, obj: Any) =
+        container.removeView(obj as View)
+
+    override fun instantiateItem(container: ViewGroup, position: Int): Any {
+        val inflater = LayoutInflater.from(container.context)
+        val layout = inflater.inflate(PAGE_LAYOUTS[position], container, false) as ViewGroup
+
+        // If final page
+        if (position == PAGE_LAYOUTS.size - 1) {
+            // Add link to more information
+            val moreInfo = layout.findViewById<TextView>(R.id.welcomeInfo)
+            setUnderlinedText(moreInfo, R.string.welcome_help_button_text)
+            moreInfo.setOnClickListener {
+                handleWebUrl(
+                    container.context,
+                    "https://commons.wikimedia.org/wiki/Help:Contents".toUri()
+                )
+            }
+
+            // Handle click of finishTutorialButton ("YES!" button) inside layout
+            layout.findViewById<View>(R.id.finishTutorialButton)
+                .setOnClickListener { view: View? -> (container.context as WelcomeActivity).finishTutorial() }
+        }
+
+        container.addView(layout)
+        return layout
+    }
+
+    companion object {
+        private val PAGE_LAYOUTS = intArrayOf(
+            R.layout.welcome_wikipedia,
+            R.layout.welcome_do_upload,
+            R.layout.welcome_dont_upload,
+            R.layout.welcome_image_example,
+            R.layout.welcome_final
+        )
+    }
+}

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

@@ -59,7 +59,7 @@ class CategoryDetailsActivity : BaseActivity(),
         val view = binding.root
         setContentView(view)
         supportFragmentManager = getSupportFragmentManager()
-        viewPagerAdapter = ViewPagerAdapter(supportFragmentManager)
+        viewPagerAdapter = ViewPagerAdapter(this, supportFragmentManager)
         binding.viewPager.adapter = viewPagerAdapter
         binding.viewPager.offscreenPageLimit = 2
         binding.tabLayout.setupWithViewPager(binding.viewPager)
@@ -83,8 +83,6 @@ class CategoryDetailsActivity : BaseActivity(),
      * Set the fragments according to the tab selected in the viewPager.
      */
     private fun setTabs() {
-        val fragmentList = mutableListOf<Fragment>()
-        val titleList = mutableListOf<String>()
         categoriesMediaFragment = CategoriesMediaFragment()
         val subCategoryListFragment = SubCategoriesFragment()
         val parentCategoriesFragment = ParentCategoriesFragment()
@@ -99,13 +97,12 @@ class CategoryDetailsActivity : BaseActivity(),
 
             viewModel.onCheckIfBookmarked(categoryName!!)
         }
-        fragmentList.add(categoriesMediaFragment)
+
-        titleList.add("MEDIA")
+        viewPagerAdapter.setTabs(
-        fragmentList.add(subCategoryListFragment)
+            R.string.title_for_media to categoriesMediaFragment,
-        titleList.add("SUBCATEGORIES")
+            R.string.title_for_subcategories to subCategoryListFragment,
-        fragmentList.add(parentCategoriesFragment)
+            R.string.title_for_parent_categories to parentCategoriesFragment
-        titleList.add("PARENT CATEGORIES")
+        )
-        viewPagerAdapter.setTabData(fragmentList, titleList)
         viewPagerAdapter.notifyDataSetChanged()
     }
 

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

@@ -12,7 +12,6 @@ import androidx.fragment.app.FragmentManager
 import androidx.work.ExistingWorkPolicy
 import com.google.android.material.bottomnavigation.BottomNavigationView
 import fr.free.nrw.commons.R
-import fr.free.nrw.commons.WelcomeActivity
 import fr.free.nrw.commons.auth.SessionManager
 import fr.free.nrw.commons.bookmarks.BookmarkFragment
 import fr.free.nrw.commons.contributions.ContributionsFragment.Companion.newInstance
@@ -33,6 +32,7 @@ import fr.free.nrw.commons.notification.NotificationActivity.Companion.startYour
 import fr.free.nrw.commons.notification.NotificationController
 import fr.free.nrw.commons.quiz.QuizChecker
 import fr.free.nrw.commons.settings.SettingsFragment
+import fr.free.nrw.commons.startWelcome
 import fr.free.nrw.commons.theme.BaseActivity
 import fr.free.nrw.commons.upload.UploadProgressActivity
 import fr.free.nrw.commons.upload.worker.WorkRequestHelper.Companion.makeOneTimeWorkRequest
@@ -517,7 +517,7 @@ after opening the app.
             (!applicationKvStore!!.getBoolean("login_skipped"))
         ) {
             defaultKvStore.putBoolean("inAppCameraFirstRun", true)
-            WelcomeActivity.startYourself(this)
+            startWelcome()
         }
 
         retryAllFailedUploads()

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

@@ -1,6 +1,7 @@
 package fr.free.nrw.commons.explore;
 
 import static androidx.viewpager.widget.ViewPager.SCROLL_STATE_IDLE;
+import static fr.free.nrw.commons.ViewPagerAdapter.pairOf;
 
 import android.os.Bundle;
 import android.view.LayoutInflater;
@@ -23,10 +24,12 @@ import fr.free.nrw.commons.kvstore.JsonKvStore;
 import fr.free.nrw.commons.theme.BaseActivity;
 import fr.free.nrw.commons.utils.ActivityUtils;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Locale;
 import javax.inject.Inject;
 import javax.inject.Named;
+import kotlin.Pair;
 
 public class ExploreFragment extends CommonsDaggerSupportFragment {
 
@@ -70,7 +73,7 @@ public class ExploreFragment extends CommonsDaggerSupportFragment {
         loadNearbyMapData();
         binding = FragmentExploreBinding.inflate(inflater, container, false);
 
-        viewPagerAdapter = new ViewPagerAdapter(getChildFragmentManager(),
+        viewPagerAdapter = new ViewPagerAdapter(requireContext(), getChildFragmentManager(),
             FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
 
         binding.viewPager.setAdapter(viewPagerAdapter);
@@ -111,9 +114,6 @@ public class ExploreFragment extends CommonsDaggerSupportFragment {
      * Sets the titles in the tabLayout and fragments in the viewPager
      */
     public void setTabs() {
-        List<Fragment> fragmentList = new ArrayList<>();
-        List<String> titleList = new ArrayList<>();
-
         Bundle featuredArguments = new Bundle();
         featuredArguments.putString("categoryName", FEATURED_IMAGES_CATEGORY);
 
@@ -133,19 +133,15 @@ public class ExploreFragment extends CommonsDaggerSupportFragment {
         featuredRootFragment = new ExploreListRootFragment(featuredArguments);
         mobileRootFragment = new ExploreListRootFragment(mobileArguments);
         mapRootFragment = new ExploreMapRootFragment(mapArguments);
-        fragmentList.add(featuredRootFragment);
-        titleList.add(getString(R.string.explore_tab_title_featured).toUpperCase(Locale.ROOT));
-
-        fragmentList.add(mobileRootFragment);
-        titleList.add(getString(R.string.explore_tab_title_mobile).toUpperCase(Locale.ROOT));
-
-        fragmentList.add(mapRootFragment);
-        titleList.add(getString(R.string.explore_tab_title_map).toUpperCase(Locale.ROOT));
 
         ((MainActivity) getActivity()).showTabs();
         ((BaseActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(false);
 
-        viewPagerAdapter.setTabData(fragmentList, titleList);
+        viewPagerAdapter.setTabs(
+            pairOf(R.string.explore_tab_title_featured, featuredRootFragment),
+            pairOf(R.string.explore_tab_title_mobile, mobileRootFragment),
+            pairOf(R.string.explore_tab_title_map, mapRootFragment)
+        );
         viewPagerAdapter.notifyDataSetChanged();
     }
 

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

@@ -1,5 +1,7 @@
 package fr.free.nrw.commons.explore;
 
+import static fr.free.nrw.commons.ViewPagerAdapter.pairOf;
+
 import android.os.Bundle;
 import android.text.TextUtils;
 import android.view.View;
@@ -26,11 +28,13 @@ import fr.free.nrw.commons.utils.FragmentUtils;
 import fr.free.nrw.commons.utils.ViewUtil;
 import io.reactivex.android.schedulers.AndroidSchedulers;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Date;
 import java.util.List;
 import java.util.Locale;
 import java.util.concurrent.TimeUnit;
 import javax.inject.Inject;
+import kotlin.Pair;
 import timber.log.Timber;
 
 /**
@@ -65,7 +69,7 @@ public class SearchActivity extends BaseActivity
         binding.toolbarSearch.setNavigationOnClickListener(v->onBackPressed());
         supportFragmentManager = getSupportFragmentManager();
         setSearchHistoryFragment();
-        viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
+        viewPagerAdapter = new ViewPagerAdapter(this, getSupportFragmentManager());
         binding.viewPager.setAdapter(viewPagerAdapter);
         binding.viewPager.setOffscreenPageLimit(2); // Because we want all the fragments to be alive
         binding.tabLayout.setupWithViewPager(binding.viewPager);
@@ -90,19 +94,15 @@ public class SearchActivity extends BaseActivity
      * Sets the titles in the tabLayout and fragments in the viewPager
      */
     public void setTabs() {
-        List<Fragment> fragmentList = new ArrayList<>();
-        List<String> titleList = new ArrayList<>();
         searchMediaFragment = new SearchMediaFragment();
         searchDepictionsFragment = new SearchDepictionsFragment();
         searchCategoryFragment= new SearchCategoryFragment();
-        fragmentList.add(searchMediaFragment);
-        titleList.add(getResources().getString(R.string.search_tab_title_media).toUpperCase(Locale.ROOT));
-        fragmentList.add(searchCategoryFragment);
-        titleList.add(getResources().getString(R.string.search_tab_title_categories).toUpperCase(Locale.ROOT));
-        fragmentList.add(searchDepictionsFragment);
-        titleList.add(getResources().getString(R.string.search_tab_title_depictions).toUpperCase(Locale.ROOT));
 
-        viewPagerAdapter.setTabData(fragmentList, titleList);
+        viewPagerAdapter.setTabs(
+            pairOf(R.string.search_tab_title_media, searchMediaFragment),
+            pairOf(R.string.search_tab_title_categories, searchCategoryFragment),
+            pairOf(R.string.search_tab_title_depictions, searchDepictionsFragment)
+        );
         viewPagerAdapter.notifyDataSetChanged();
         getCompositeDisposable().add(RxSearchView.queryTextChanges(binding.searchBox)
                 .takeUntil(RxView.detaches(binding.searchBox))

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

@@ -1,5 +1,6 @@
 package fr.free.nrw.commons.explore.depictions;
 
+import static fr.free.nrw.commons.ViewPagerAdapter.pairOf;
 import static fr.free.nrw.commons.utils.UrlUtilsKt.handleWebUrl;
 
 import android.content.Context;
@@ -31,8 +32,10 @@ import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.disposables.CompositeDisposable;
 import io.reactivex.schedulers.Schedulers;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import javax.inject.Inject;
+import kotlin.Pair;
 
 /**
  * Activity to show depiction media, parent classes and child classes of depicted items in Explore
@@ -66,7 +69,7 @@ public class WikidataItemDetailsActivity extends BaseActivity implements MediaDe
         setContentView(binding.getRoot());
         compositeDisposable = new CompositeDisposable();
         supportFragmentManager = getSupportFragmentManager();
-        viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
+        viewPagerAdapter = new ViewPagerAdapter(this, getSupportFragmentManager());
         binding.viewPager.setAdapter(viewPagerAdapter);
         binding.viewPager.setOffscreenPageLimit(2);
         binding.tabLayout.setupWithViewPager(binding.viewPager);
@@ -105,8 +108,6 @@ public class WikidataItemDetailsActivity extends BaseActivity implements MediaDe
      * Set the fragments according to the tab selected in the viewPager.
      */
     private void setTabs() {
-        List<Fragment> fragmentList = new ArrayList<>();
-        List<String> titleList = new ArrayList<>();
         depictionImagesListFragment = new DepictedImagesFragment();
         ChildDepictionsFragment childDepictionsFragment = new ChildDepictionsFragment();
         ParentDepictionsFragment parentDepictionsFragment = new ParentDepictionsFragment();
@@ -120,13 +121,12 @@ public class WikidataItemDetailsActivity extends BaseActivity implements MediaDe
             parentDepictionsFragment.setArguments(arguments);
             childDepictionsFragment.setArguments(arguments);
         }
-        fragmentList.add(depictionImagesListFragment);
+
-        titleList.add(getResources().getString(R.string.title_for_media));
+        viewPagerAdapter.setTabs(
-        fragmentList.add(childDepictionsFragment);
+            pairOf(R.string.title_for_media, depictionImagesListFragment),
-        titleList.add(getResources().getString(R.string.title_for_child_classes));
+            pairOf(R.string.title_for_subcategories, childDepictionsFragment),
-        fragmentList.add(parentDepictionsFragment);
+            pairOf(R.string.title_for_parent_categories, parentDepictionsFragment)
-        titleList.add(getResources().getString(R.string.title_for_parent_classes));
+        );
-        viewPagerAdapter.setTabData(fragmentList, titleList);
         binding.viewPager.setOffscreenPageLimit(2);
         viewPagerAdapter.notifyDataSetChanged();
 

app/src/main/java/fr/free/nrw/commons/explore/map/ExploreMapCalls.java

@@ -1,8 +1,10 @@
 package fr.free.nrw.commons.explore.map;
 
+import androidx.annotation.NonNull;
 import fr.free.nrw.commons.Media;
 import fr.free.nrw.commons.location.LatLng;
 import fr.free.nrw.commons.media.MediaClient;
+import java.util.Collections;
 import java.util.List;
 import javax.inject.Inject;
 import javax.inject.Singleton;
@@ -23,6 +25,7 @@ public class ExploreMapCalls {
      * @param currentLatLng coordinates of search location
      * @return list of places obtained
      */
+    @NonNull
     List<Media> callCommonsQuery(final LatLng currentLatLng) {
         String coordinates = currentLatLng.getLatitude() + "|" + currentLatLng.getLongitude();
         return mediaClient.getMediaListFromGeoSearch(coordinates).blockingGet();

app/src/main/java/fr/free/nrw/commons/explore/map/ExploreMapPresenter.java

@@ -14,6 +14,7 @@ import fr.free.nrw.commons.explore.map.ExploreMapController.NearbyBaseMarkerThum
 import fr.free.nrw.commons.kvstore.JsonKvStore;
 import fr.free.nrw.commons.location.LatLng;
 import fr.free.nrw.commons.location.LocationServiceManager.LocationChangeType;
+import fr.free.nrw.commons.nearby.Place;
 import io.reactivex.Observable;
 import java.lang.reflect.Proxy;
 import java.util.List;
@@ -182,7 +183,7 @@ public class ExploreMapPresenter
         exploreMapController
             .loadAttractionsFromLocationToBaseMarkerOptions(explorePlacesInfo.currentLatLng,
                 // Curlatlang will be used to calculate distances
-                explorePlacesInfo.explorePlaceList,
+                (List<Place>) explorePlacesInfo.explorePlaceList,
                 exploreMapFragmentView.getContext(),
                 this,
                 explorePlacesInfo);
@@ -230,11 +231,7 @@ public class ExploreMapPresenter
         mylocation.setLongitude(exploreMapFragmentView.getLastMapFocus().getLongitude());
         Float distance = mylocation.distanceTo(dest_location);
 
-        if (distance > 2000.0 * 3 / 4) {
+        return !(distance > 2000.0 * 3 / 4);
-            return false;
-        } else {
-            return true;
-        }
     }
 
 }

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

@@ -1,6 +1,6 @@
 package fr.free.nrw.commons.media
 
-import fr.free.nrw.commons.OkHttpConnectionFactory.UnsuccessfulResponseInterceptor.SUPPRESS_ERROR_LOG_HEADER
+import fr.free.nrw.commons.SUPPRESS_ERROR_LOG_HEADER
 import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
 import io.reactivex.Single
 import retrofit2.http.GET

app/src/main/java/fr/free/nrw/commons/navtab/MoreBottomSheetFragment.kt

@@ -18,7 +18,6 @@ import fr.free.nrw.commons.BuildConfig
 import fr.free.nrw.commons.CommonsApplication
 import fr.free.nrw.commons.CommonsApplication.ActivityLogoutListener
 import fr.free.nrw.commons.R
-import fr.free.nrw.commons.WelcomeActivity
 import fr.free.nrw.commons.actions.PageEditClient
 import fr.free.nrw.commons.databinding.FragmentMoreBottomSheetBinding
 import fr.free.nrw.commons.di.ApplicationlessInjection
@@ -32,6 +31,7 @@ import fr.free.nrw.commons.logging.CommonsLogSender
 import fr.free.nrw.commons.profile.ProfileActivity
 import fr.free.nrw.commons.review.ReviewActivity
 import fr.free.nrw.commons.settings.SettingsActivity
+import fr.free.nrw.commons.startWelcome
 import io.reactivex.Single
 import io.reactivex.android.schedulers.AndroidSchedulers
 import io.reactivex.schedulers.Schedulers
@@ -241,7 +241,7 @@ class MoreBottomSheetFragment : BottomSheetDialogFragment() {
     }
 
     fun onTutorialClicked() {
-        WelcomeActivity.startYourself(requireActivity())
+        requireContext().startWelcome()
     }
 
     fun onSettingsClicked() {

app/src/main/java/fr/free/nrw/commons/nearby/NearbyPlaces.java

@@ -1,10 +1,14 @@
 package fr.free.nrw.commons.nearby;
 
+import static java.util.Collections.emptyList;
+
 import android.location.Location;
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import fr.free.nrw.commons.nearby.model.NearbyQueryParams;
+import fr.free.nrw.commons.nearby.model.NearbyQueryParams.Radial;
+import fr.free.nrw.commons.nearby.model.NearbyQueryParams.Rectangular;
 import java.io.IOException;
-import java.util.Collections;
 import java.util.List;
 
 import javax.inject.Inject;
@@ -46,13 +50,14 @@ public class NearbyPlaces {
      * @param customQuery
      * @return list of places obtained
      */
+    @NonNull
     List<Place> radiusExpander(final LatLng currentLatLng, final String lang,
         final boolean returnClosestResult, @Nullable final String customQuery) throws Exception {
 
         final int minResults;
         final double maxRadius;
 
-        List<Place> places = Collections.emptyList();
+        List<Place> places = emptyList();
 
         // If returnClosestResult is true, then this means that we are trying to get closest point
         // to use in cardView in Contributions fragment
@@ -113,6 +118,7 @@ public class NearbyPlaces {
      * @return A list of places obtained from the Wikidata query.
      * @throws Exception If an error occurs during the retrieval process.
      */
+    @NonNull
     public List<Place> getFromWikidataQuery(
         final fr.free.nrw.commons.location.LatLng centerPoint,
         final fr.free.nrw.commons.location.LatLng screenTopRight,
@@ -120,11 +126,11 @@ public class NearbyPlaces {
         final boolean shouldQueryForMonuments,
         @Nullable final String customQuery) throws Exception {
         if (customQuery != null) {
-            return okHttpJsonApiClient
+            final List<Place> nearbyPlaces = okHttpJsonApiClient.getNearbyPlaces(
-                .getNearbyPlaces(
+                    new Rectangular(screenTopRight, screenBottomLeft), lang,
-                    new NearbyQueryParams.Rectangular(screenTopRight, screenBottomLeft), lang,
                     shouldQueryForMonuments,
                     customQuery);
+            return nearbyPlaces != null ? nearbyPlaces : emptyList();
         }
 
         final int lowerLimit = 1000, upperLimit = 1500;
@@ -141,9 +147,10 @@ public class NearbyPlaces {
             final int itemCount = okHttpJsonApiClient.getNearbyItemCount(
                 new NearbyQueryParams.Rectangular(screenTopRight, screenBottomLeft));
             if (itemCount < upperLimit) {
-                return okHttpJsonApiClient.getNearbyPlaces(
+                final List<Place> nearbyPlaces = okHttpJsonApiClient.getNearbyPlaces(
-                    new NearbyQueryParams.Rectangular(screenTopRight, screenBottomLeft), lang,
+                    new Rectangular(screenTopRight, screenBottomLeft), lang,
                     shouldQueryForMonuments, null);
+                return nearbyPlaces != null ? nearbyPlaces : emptyList();
             }
         }
 
@@ -175,9 +182,10 @@ public class NearbyPlaces {
                 maxRadius = targetRadius - 1;
             }
         }
-        return okHttpJsonApiClient.getNearbyPlaces(
+        final List<Place> nearbyPlaces = okHttpJsonApiClient.getNearbyPlaces(
-            new NearbyQueryParams.Radial(centerPoint, targetRadius / 100f), lang, shouldQueryForMonuments,
+            new Radial(centerPoint, targetRadius / 100f), lang, shouldQueryForMonuments,
             null);
+        return nearbyPlaces != null ? nearbyPlaces : emptyList();
     }
 
     /**

app/src/main/java/fr/free/nrw/commons/profile/ProfileActivity.kt

@@ -11,6 +11,7 @@ import android.view.View
 import android.widget.ImageView
 import android.widget.TextView
 import androidx.core.content.FileProvider
+import androidx.core.os.bundleOf
 import androidx.fragment.app.Fragment
 import fr.free.nrw.commons.R
 import fr.free.nrw.commons.ViewPagerAdapter
@@ -71,7 +72,7 @@ class ProfileActivity : BaseActivity() {
         title = userName
         shouldShowContributions = intent.getBooleanExtra(KEY_SHOULD_SHOW_CONTRIBUTIONS, false)
 
-        viewPagerAdapter = ViewPagerAdapter(supportFragmentManager)
+        viewPagerAdapter = ViewPagerAdapter(this, supportFragmentManager)
         binding.viewPager.adapter = viewPagerAdapter
         binding.tabLayout.setupWithViewPager(binding.viewPager)
         setTabs()
@@ -83,39 +84,23 @@ class ProfileActivity : BaseActivity() {
     }
 
     private fun setTabs() {
-        val fragmentList = mutableListOf<Fragment>()
-        val titleList = mutableListOf<String>()
-
-        // Add Achievements tab
         achievementsFragment = AchievementsFragment().apply {
-            arguments = Bundle().apply {
+            arguments = bundleOf(KEY_USERNAME to userName)
-                putString(KEY_USERNAME, userName)
         }
-        }
-        fragmentList.add(achievementsFragment)
-        titleList.add(resources.getString(R.string.achievements_tab_title).uppercase())
 
-        // Add Leaderboard tab
         leaderboardFragment = LeaderboardFragment().apply {
-            arguments = Bundle().apply {
+            arguments = bundleOf(KEY_USERNAME to userName)
-                putString(KEY_USERNAME, userName)
         }
-        }
-        fragmentList.add(leaderboardFragment)
-        titleList.add(resources.getString(R.string.leaderboard_tab_title).uppercase(Locale.ROOT))
 
-        // Add Contributions tab
         contributionsFragment = ContributionsFragment().apply {
-            arguments = Bundle().apply {
+            arguments = bundleOf(KEY_USERNAME to userName)
-                putString(KEY_USERNAME, userName)
-            }
-        }
-        contributionsFragment?.let {
-            fragmentList.add(it)
-            titleList.add(getString(R.string.contributions_fragment).uppercase(Locale.ROOT))
         }
 
-        viewPagerAdapter.setTabData(fragmentList, titleList)
+        viewPagerAdapter.setTabs(
+            R.string.achievements_tab_title to achievementsFragment,
+            R.string.leaderboard_tab_title to leaderboardFragment,
+            R.string.contributions_fragment to contributionsFragment!!
+        )
         viewPagerAdapter.notifyDataSetChanged()
     }
 

app/src/main/java/fr/free/nrw/commons/upload/UploadProgressActivity.kt

@@ -28,8 +28,6 @@ class UploadProgressActivity : BaseActivity() {
     @Inject
     lateinit var contributionDao: ContributionDao
 
-    val fragmentList: MutableList<Fragment> = ArrayList()
-    val titleList: MutableList<String> = ArrayList()
     var isPaused = true
     var isPendingIconsVisible = true
     var isErrorIconsVisisble = false
@@ -38,7 +36,7 @@ class UploadProgressActivity : BaseActivity() {
         super.onCreate(savedInstanceState)
         binding = ActivityUploadProgressBinding.inflate(layoutInflater)
         setContentView(binding.root)
-        viewPagerAdapter = ViewPagerAdapter(supportFragmentManager)
+        viewPagerAdapter = ViewPagerAdapter(this, supportFragmentManager)
         binding.uploadProgressViewPager.setAdapter(viewPagerAdapter)
         binding.uploadProgressViewPager.setId(R.id.upload_progress_view_pager)
         binding.uploadProgressTabLayout.setupWithViewPager(binding.uploadProgressViewPager)
@@ -81,11 +79,10 @@ class UploadProgressActivity : BaseActivity() {
         pendingUploadsFragment = PendingUploadsFragment()
         failedUploadsFragment = FailedUploadsFragment()
 
-        fragmentList.add(pendingUploadsFragment!!)
+        viewPagerAdapter!!.setTabs(
-        titleList.add(getString(R.string.pending))
+            R.string.pending to pendingUploadsFragment!!,
-        fragmentList.add(failedUploadsFragment!!)
+            R.string.failed to failedUploadsFragment!!
-        titleList.add(getString(R.string.failed))
+        )
-        viewPagerAdapter!!.setTabData(fragmentList, titleList)
         viewPagerAdapter!!.notifyDataSetChanged()
     }
 

app/src/main/res/values/strings.xml

@@ -617,6 +617,8 @@ Upload your first media by tapping on the add button.</string>
   <string name="title_for_media">MEDIA</string>
   <string name="title_for_child_classes">CHILD CLASSES</string>
   <string name="title_for_parent_classes">PARENT CLASSES</string>
+  <string name="title_for_subcategories">SUBCATEGORIES</string>
+  <string name="title_for_parent_categories">PARENT CATEGORIES</string>
 
   <string name="upload_nearby_place_found_title">Nearby Place Found</string>
   <string name="upload_nearby_place_found_description_plural">Are these pictures of %1$s?</string>

app/src/test/kotlin/fr/free/nrw/commons/MockWebServerTest.java

@@ -1,110 +0,0 @@
-package fr.free.nrw.commons;
-
-import static fr.free.nrw.commons.TestConnectionFactoryKt.createTestClient;
-
-import androidx.annotation.NonNull;
-import java.util.List;
-import java.util.concurrent.AbstractExecutorService;
-import java.util.concurrent.Executor;
-import java.util.concurrent.TimeUnit;
-import okhttp3.Dispatcher;
-import okhttp3.OkHttpClient;
-import okhttp3.mockwebserver.MockResponse;
-import org.junit.After;
-import org.junit.Before;
-import org.junit.runner.RunWith;
-import org.robolectric.RobolectricTestRunner;
-import fr.free.nrw.commons.wikidata.GsonUtil;
-import retrofit2.Retrofit;
-import retrofit2.converter.gson.GsonConverterFactory;
-
-@RunWith(RobolectricTestRunner.class)
-public abstract class MockWebServerTest {
-    private OkHttpClient okHttpClient;
-    private final TestWebServer server = new TestWebServer();
-
-    @Before public void setUp() throws Throwable {
-        OkHttpConnectionFactory.CLIENT = createTestClient();
-        okHttpClient = OkHttpConnectionFactory.CLIENT.newBuilder()
-            .dispatcher(new Dispatcher(new ImmediateExecutorService())).build();
-        server.setUp();
-    }
-
-    @After public void tearDown() throws Throwable {
-        server.tearDown();
-    }
-
-    @NonNull protected TestWebServer server() {
-        return server;
-    }
-
-    protected void enqueueFromFile(@NonNull String filename) throws Throwable {
-        String json = TestFileUtil.readRawFile(filename);
-        server.enqueue(json);
-    }
-
-    protected void enqueue404() {
-        final int code = 404;
-        server.enqueue(new MockResponse().setResponseCode(code).setBody("Not Found"));
-    }
-
-    protected void enqueueMalformed() {
-        server.enqueue("(╯°□°）╯︵ ┻━┻");
-    }
-
-    protected void enqueueEmptyJson() {
-        server.enqueue(new MockResponse().setBody("{}"));
-    }
-
-    @NonNull protected OkHttpClient okHttpClient() {
-        return okHttpClient;
-    }
-
-    @NonNull protected <T> T service(Class<T> clazz) {
-        return service(clazz, server().getUrl());
-    }
-
-    @NonNull protected <T> T service(Class<T> clazz, @NonNull String url) {
-        return new Retrofit.Builder()
-                .baseUrl(url)
-                .callbackExecutor(new ImmediateExecutor())
-                .client(okHttpClient)
-                .addConverterFactory(GsonConverterFactory.create(GsonUtil.INSTANCE.getDefaultGson()))
-                .build()
-                .create(clazz);
-    }
-
-    public final class ImmediateExecutorService extends AbstractExecutorService {
-        @Override public void shutdown() {
-            throw new UnsupportedOperationException();
-        }
-
-        @NonNull @Override public List<Runnable> shutdownNow() {
-            throw new UnsupportedOperationException();
-        }
-
-        @Override public boolean isShutdown() {
-            throw new UnsupportedOperationException();
-        }
-
-        @Override public boolean isTerminated() {
-            throw new UnsupportedOperationException();
-        }
-
-        @Override public boolean awaitTermination(long l, @NonNull TimeUnit timeUnit)
-            throws InterruptedException {
-            throw new UnsupportedOperationException();
-        }
-
-        @Override public void execute(@NonNull Runnable runnable) {
-            runnable.run();
-        }
-    }
-
-    public class ImmediateExecutor implements Executor {
-        @Override
-        public void execute(@NonNull Runnable runnable) {
-            runnable.run();
-        }
-    }
-}

app/src/test/kotlin/fr/free/nrw/commons/MockWebServerTest.kt

@@ -0,0 +1,110 @@
+package fr.free.nrw.commons
+
+import fr.free.nrw.commons.wikidata.GsonUtil.defaultGson
+import okhttp3.Dispatcher
+import okhttp3.OkHttpClient
+import okhttp3.mockwebserver.MockResponse
+import org.junit.After
+import org.junit.Before
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import retrofit2.Retrofit
+import retrofit2.converter.gson.GsonConverterFactory
+import java.util.concurrent.AbstractExecutorService
+import java.util.concurrent.Executor
+import java.util.concurrent.TimeUnit
+
+@RunWith(RobolectricTestRunner::class)
+abstract class MockWebServerTest {
+    private var okHttpClient: OkHttpClient? = null
+    private val server = TestWebServer()
+
+    @Before
+    @Throws(Throwable::class)
+    open fun setUp() {
+        OkHttpConnectionFactory.CLIENT = createTestClient()
+        okHttpClient = OkHttpConnectionFactory.CLIENT!!.newBuilder()
+            .dispatcher(Dispatcher(ImmediateExecutorService())).build()
+        server.setUp()
+    }
+
+    @After
+    @Throws(Throwable::class)
+    fun tearDown() {
+        server.tearDown()
+    }
+
+    protected fun server(): TestWebServer {
+        return server
+    }
+
+    @Throws(Throwable::class)
+    protected fun enqueueFromFile(filename: String) {
+        val json = TestFileUtil.readRawFile(filename)
+        server.enqueue(json)
+    }
+
+    protected fun enqueue404() {
+        val code = 404
+        server.enqueue(MockResponse().setResponseCode(code).setBody("Not Found"))
+    }
+
+    protected fun enqueueMalformed() {
+        server.enqueue("(╯°□°）╯︵ ┻━┻")
+    }
+
+    protected fun enqueueEmptyJson() {
+        server.enqueue(MockResponse().setBody("{}"))
+    }
+
+    protected fun okHttpClient(): OkHttpClient {
+        return okHttpClient!!
+    }
+
+    protected fun <T> service(clazz: Class<T>): T {
+        return service(clazz, server().url)
+    }
+
+    protected fun <T> service(clazz: Class<T>, url: String): T {
+        return Retrofit.Builder()
+            .baseUrl(url)
+            .callbackExecutor(ImmediateExecutor())
+            .client(okHttpClient)
+            .addConverterFactory(GsonConverterFactory.create(defaultGson))
+            .build()
+            .create(clazz)
+    }
+
+    inner class ImmediateExecutorService : AbstractExecutorService() {
+        override fun shutdown() {
+            throw UnsupportedOperationException()
+        }
+
+        override fun shutdownNow(): List<Runnable> {
+            throw UnsupportedOperationException()
+        }
+
+        override fun isShutdown(): Boolean {
+            throw UnsupportedOperationException()
+        }
+
+        override fun isTerminated(): Boolean {
+            throw UnsupportedOperationException()
+        }
+
+        @Throws(InterruptedException::class)
+        override fun awaitTermination(l: Long, timeUnit: TimeUnit): Boolean {
+            throw UnsupportedOperationException()
+        }
+
+        override fun execute(runnable: Runnable) {
+            runnable.run()
+        }
+    }
+
+    inner class ImmediateExecutor : Executor {
+        override fun execute(runnable: Runnable) {
+            runnable.run()
+        }
+    }
+}

app/src/test/kotlin/fr/free/nrw/commons/TestConnectionFactory.kt

@@ -1,6 +1,5 @@
 package fr.free.nrw.commons
 
-import fr.free.nrw.commons.OkHttpConnectionFactory.HttpStatusException
 import okhttp3.Interceptor
 import okhttp3.OkHttpClient
 import okhttp3.Response
@@ -39,6 +38,6 @@ private class UnsuccessfulResponseInterceptor : Interceptor {
         if (rsp.isSuccessful) {
             return rsp
         }
-        throw HttpStatusException(rsp)
+        throw IOException("Unsuccessful response")
     }
 }

app/src/test/kotlin/fr/free/nrw/commons/auth/csrf/CsrfTokenClientTest.kt

@@ -2,7 +2,6 @@ package fr.free.nrw.commons.auth.csrf
 
 import com.google.gson.stream.MalformedJsonException
 import fr.free.nrw.commons.MockWebServerTest
-import fr.free.nrw.commons.OkHttpConnectionFactory.HttpStatusException
 import fr.free.nrw.commons.auth.SessionManager
 import fr.free.nrw.commons.auth.login.LoginClient
 import fr.free.nrw.commons.wikidata.mwapi.MwException
@@ -13,6 +12,7 @@ import org.mockito.ArgumentMatchers.isA
 import org.mockito.Mockito.mock
 import org.mockito.Mockito.never
 import org.mockito.Mockito.verify
+import java.io.IOException
 
 class CsrfTokenClientTest : MockWebServerTest() {
     private val cb = mock(CsrfTokenClient.Callback::class.java)
@@ -53,7 +53,7 @@ class CsrfTokenClientTest : MockWebServerTest() {
         performRequest()
 
         verify(cb, never()).success(any(String::class.java))
-        verify(cb).failure(isA(HttpStatusException::class.java))
+        verify(cb).failure(isA(IOException::class.java))
     }
 
     @Test