Feat: Make it smoother to switch between nearby and explore maps

.gitignore

@@ -46,4 +46,5 @@ captures/*
 
 # Test and other output
 app/jacoco.exec
-app/CommonsContributions
+app/CommonsContributions
+app/.*

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

@@ -207,6 +207,9 @@ private void setUpLoggedOutPager() {
     private boolean loadFragment(Fragment fragment, boolean showBottom) {
         //showBottom so that we do not show the bottom tray again when constructing
         //from the saved instance state.
+
+        freeUpFragments();
+
         if (fragment instanceof ContributionsFragment) {
             if (activeFragment == ActiveFragment.CONTRIBUTIONS) {
                 // scroll to top if already on the Contributions tab
@@ -256,6 +259,31 @@ private boolean loadFragment(Fragment fragment, boolean showBottom) {
         return false;
     }
 
+    /**
+     * loadFragment() overload that supports passing extras to fragments
+     **/
+    private boolean loadFragment(Fragment fragment, boolean showBottom, Bundle args) {
+        if (fragment != null && args != null) {
+            fragment.setArguments(args);
+        }
+
+        return loadFragment(fragment, showBottom);
+    }
+
+    /**
+     * Old implementation of loadFragment() was causing memory leaks, due to MainActivity holding
+     * references to cleared fragments. This function frees up all fragment references.
+     * <p>
+     * Called in loadFragment() before doing the actual loading.
+     **/
+    public void freeUpFragments() {
+        // free all fragments except contributionsFragment because several tests depend on it.
+        // hence, contributionsFragment is probably still a leak
+        nearbyParentFragment = null;
+        exploreFragment = null;
+        bookmarkFragment = null;
+    }
+
     public void hideTabs() {
         binding.fragmentMainNavTabLayout.setVisibility(View.GONE);
     }
@@ -432,6 +460,42 @@ public void onReady() {
             });
     }
 
+    /**
+     * Launch the Explore fragment from Nearby fragment. This method is called when a user clicks
+     * the 'Show in Explore' option in the 3-dots menu in Nearby.
+     *
+     * @param zoom      current zoom of Nearby map
+     * @param latitude  current latitude of Nearby map
+     * @param longitude current longitude of Nearby map
+     **/
+    public void loadExploreMapFromNearby(double zoom, double latitude, double longitude) {
+        Bundle bundle = new Bundle();
+        bundle.putDouble("prev_zoom", zoom);
+        bundle.putDouble("prev_latitude", latitude);
+        bundle.putDouble("prev_longitude", longitude);
+
+        loadFragment(ExploreFragment.newInstance(), false, bundle);
+        setSelectedItemId(NavTab.EXPLORE.code());
+    }
+
+    /**
+     * Launch the Nearby fragment from Explore fragment. This method is called when a user clicks
+     * the 'Show in Nearby' option in the 3-dots menu in Explore.
+     *
+     * @param zoom      current zoom of Explore map
+     * @param latitude  current latitude of Explore map
+     * @param longitude current longitude of Explore map
+     **/
+    public void loadNearbyMapFromExplore(double zoom, double latitude, double longitude) {
+        Bundle bundle = new Bundle();
+        bundle.putDouble("prev_zoom", zoom);
+        bundle.putDouble("prev_latitude", latitude);
+        bundle.putDouble("prev_longitude", longitude);
+
+        loadFragment(NearbyParentFragment.newInstance(), false, bundle);
+        setSelectedItemId(NavTab.NEARBY.code());
+    }
+
     @Override
     protected void onResume() {
         super.onResume();

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

@@ -1,5 +1,7 @@
 package fr.free.nrw.commons.explore;
 
+import static androidx.viewpager.widget.ViewPager.SCROLL_STATE_IDLE;
+
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.Menu;
@@ -42,9 +44,13 @@ public class ExploreFragment extends CommonsDaggerSupportFragment {
     @Named("default_preferences")
     public JsonKvStore applicationKvStore;
 
-    public void setScroll(boolean canScroll){
-        if (binding != null)
-        {
+    // Nearby map state (for if we came from Nearby fragment)
+    private double prevZoom;
+    private double prevLatitude;
+    private double prevLongitude;
+
+    public void setScroll(boolean canScroll) {
+        if (binding != null) {
             binding.viewPager.setCanScroll(canScroll);
         }
     }
@@ -60,6 +66,7 @@ public static ExploreFragment newInstance() {
     public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
         @Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
+        loadNearbyMapData();
         binding = FragmentExploreBinding.inflate(inflater, container, false);
 
         viewPagerAdapter = new ViewPagerAdapter(getChildFragmentManager());
@@ -89,6 +96,11 @@ public void onPageScrollStateChanged(int state) {
         });
         setTabs();
         setHasOptionsMenu(true);
+
+        // if we came from 'Show in Explore' in Nearby, jump to Map tab
+        if (isCameFromNearbyMap()) {
+            binding.viewPager.setCurrentItem(2);
+        }
         return binding.getRoot();
     }
 
@@ -108,6 +120,13 @@ public void setTabs() {
         Bundle mapArguments = new Bundle();
         mapArguments.putString("categoryName", EXPLORE_MAP);
 
+        // if we came from 'Show in Explore' in Nearby, pass on zoom and center to Explore map root
+        if (isCameFromNearbyMap()) {
+            mapArguments.putDouble("prev_zoom", prevZoom);
+            mapArguments.putDouble("prev_latitude", prevLatitude);
+            mapArguments.putDouble("prev_longitude", prevLongitude);
+        }
+
         featuredRootFragment = new ExploreListRootFragment(featuredArguments);
         mobileRootFragment = new ExploreListRootFragment(mobileArguments);
         mapRootFragment = new ExploreMapRootFragment(mapArguments);
@@ -120,13 +139,35 @@ public void setTabs() {
         fragmentList.add(mapRootFragment);
         titleList.add(getString(R.string.explore_tab_title_map).toUpperCase(Locale.ROOT));
 
-        ((MainActivity)getActivity()).showTabs();
+        ((MainActivity) getActivity()).showTabs();
         ((BaseActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(false);
 
         viewPagerAdapter.setTabData(fragmentList, titleList);
         viewPagerAdapter.notifyDataSetChanged();
     }
 
+    /**
+     * Fetch Nearby map camera data from fragment arguments if any.
+     */
+    public void loadNearbyMapData() {
+        // get fragment arguments
+        if (getArguments() != null) {
+            prevZoom = getArguments().getDouble("prev_zoom");
+            prevLatitude = getArguments().getDouble("prev_latitude");
+            prevLongitude = getArguments().getDouble("prev_longitude");
+        }
+    }
+
+    /**
+     * Checks if fragment arguments contain data from Nearby map. if present, then the user
+     * navigated from Nearby using 'Show in Explore'.
+     *
+     * @return true if user navigated from Nearby map
+     **/
+    public boolean isCameFromNearbyMap() {
+        return prevZoom != 0.0 || prevLatitude != 0.0 || prevLongitude != 0.0;
+    }
+
     public boolean onBackPressed() {
         if (binding.tabLayout.getSelectedTabPosition() == 0) {
             if (featuredRootFragment.backPressed()) {
@@ -155,7 +196,38 @@ public boolean onBackPressed() {
      */
     @Override
     public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
-        inflater.inflate(R.menu.menu_search, menu);
+        // if logged in 'Show in Nearby' menu item is visible
+        if (applicationKvStore.getBoolean("login_skipped") == false) {
+            inflater.inflate(R.menu.explore_fragment_menu, menu);
+
+            MenuItem others = menu.findItem(R.id.list_item_show_in_nearby);
+
+            if (binding.viewPager.getCurrentItem() == 2) {
+                others.setVisible(true);
+            }
+
+            // if on Map tab, show all menu options, else only show search
+            binding.viewPager.addOnPageChangeListener(new OnPageChangeListener() {
+                @Override
+                public void onPageScrolled(int position, float positionOffset,
+                    int positionOffsetPixels) {
+                }
+
+                @Override
+                public void onPageSelected(int position) {
+                    others.setVisible((position == 2));
+                }
+
+                @Override
+                public void onPageScrollStateChanged(int state) {
+                    if (state == SCROLL_STATE_IDLE && binding.viewPager.getCurrentItem() == 2) {
+                        onPageSelected(2);
+                    }
+                }
+            });
+        } else {
+            inflater.inflate(R.menu.menu_search, menu);
+        }
         super.onCreateOptionsMenu(menu, inflater);
     }
 
@@ -171,6 +243,9 @@ public boolean onOptionsItemSelected(MenuItem item) {
             case R.id.action_search:
                 ActivityUtils.startActivityWithFlags(getActivity(), SearchActivity.class);
                 return true;
+            case R.id.list_item_show_in_nearby:
+                mapRootFragment.loadNearbyMapFromExplore();
+                return true;
             default:
                 return super.onOptionsItemSelected(item);
         }

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

@@ -39,10 +39,22 @@ public static ExploreMapRootFragment newInstance() {
     }
 
     public ExploreMapRootFragment(Bundle bundle) {
+        // get fragment arguments
         String title = bundle.getString("categoryName");
+        double zoom = bundle.getDouble("prev_zoom");
+        double latitude = bundle.getDouble("prev_latitude");
+        double longitude = bundle.getDouble("prev_longitude");
+
         mapFragment = new ExploreMapFragment();
         Bundle featuredArguments = new Bundle();
         featuredArguments.putString("categoryName", title);
+
+        // if we came from 'Show in Explore' in Nearby, pass on zoom and center
+        if (zoom != 0.0 || latitude != 0.0 || longitude != 0.0) {
+            featuredArguments.putDouble("prev_zoom", zoom);
+            featuredArguments.putDouble("prev_latitude", latitude);
+            featuredArguments.putDouble("prev_longitude", longitude);
+        }
         mapFragment.setArguments(featuredArguments);
     }
 
@@ -198,7 +210,8 @@ public boolean backPressed() {
             ((MainActivity) getActivity()).showTabs();
             return true;
 
-        } if (mapFragment != null && mapFragment.isVisible()) {
+        }
+        if (mapFragment != null && mapFragment.isVisible()) {
             if (mapFragment.backButtonClicked()) {
                 // Explore map fragment handled the event no further action required.
                 return true;
@@ -213,6 +226,10 @@ public boolean backPressed() {
         return false;
     }
 
+    public void loadNearbyMapFromExplore() {
+        mapFragment.loadNearbyMapFromExplore();
+    }
+
     @Override
     public void onDestroy() {
         super.onDestroy();