The viewmodels have been modified to not repeat calls to the backend during the lifecycle of the fragment

app/src/main/java/com/cappielloantonio/play/ui/dialog/PlaylistChooserDialog.java

@@ -82,7 +82,7 @@ public class PlaylistChooserDialog extends DialogFragment {
         playlistDialogHorizontalAdapter = new PlaylistDialogHorizontalAdapter(requireContext(), playlistChooserViewModel, this);
         bind.playlistDialogRecyclerView.setAdapter(playlistDialogHorizontalAdapter);
 
-        playlistChooserViewModel.getPlaylistList().observe(getViewLifecycleOwner(), playlists -> {
+        playlistChooserViewModel.getPlaylistList(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), playlists -> {
             if (playlists != null) {
                 if (playlists.size() > 0) {
                     if (bind != null) bind.noPlaylistsCreatedTextView.setVisibility(View.GONE);

app/src/main/java/com/cappielloantonio/play/ui/fragment/HomeFragment.java

@@ -256,7 +256,7 @@ public class HomeFragment extends Fragment {
         discoverSongAdapter = new DiscoverSongAdapter(activity, requireContext());
         bind.discoverSongViewPager.setAdapter(discoverSongAdapter);
         bind.discoverSongViewPager.setOffscreenPageLimit(1);
-        homeViewModel.getDiscoverSongSample().observe(getViewLifecycleOwner(), songs -> {
+        homeViewModel.getDiscoverSongSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), songs -> {
             if (songs == null) {
                 if (bind != null) bind.homeDiscoveryPlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.homeDiscoverSector.setVisibility(View.GONE);
@@ -277,7 +277,7 @@ public class HomeFragment extends Fragment {
 
         similarMusicAdapter = new SimilarTrackAdapter(activity, requireContext());
         bind.similarTracksRecyclerView.setAdapter(similarMusicAdapter);
-        homeViewModel.getStarredTracksSample().observe(getViewLifecycleOwner(), songs -> {
+        homeViewModel.getStarredTracksSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), songs -> {
             if (songs == null) {
                 if (bind != null) bind.homeSimilarTracksPlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.homeSimilarTracksSector.setVisibility(View.GONE);
@@ -299,7 +299,7 @@ public class HomeFragment extends Fragment {
 
         radioArtistAdapter = new ArtistAdapter((MainActivity) requireActivity(), requireContext());
         bind.radioArtistRecyclerView.setAdapter(radioArtistAdapter);
-        homeViewModel.getStarredArtistsSample().observe(getViewLifecycleOwner(), artists -> {
+        homeViewModel.getStarredArtistsSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), artists -> {
             if (artists == null) {
                 if (bind != null) bind.homeRadioArtistPlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.homeRadioArtistSector.setVisibility(View.GONE);

app/src/main/java/com/cappielloantonio/play/ui/fragment/LibraryFragment.java

@@ -145,7 +145,7 @@ public class LibraryFragment extends Fragment {
 
         albumAdapter = new AlbumAdapter(requireContext());
         bind.albumRecyclerView.setAdapter(albumAdapter);
-        libraryViewModel.getAlbumSample().observe(getViewLifecycleOwner(), albums -> {
+        libraryViewModel.getAlbumSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), albums -> {
             if (albums == null) {
                 if (bind != null) bind.libraryAlbumPlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.libraryAlbumSector.setVisibility(View.GONE);
@@ -167,7 +167,7 @@ public class LibraryFragment extends Fragment {
 
         artistAdapter = new ArtistAdapter((MainActivity) requireActivity(), requireContext());
         bind.artistRecyclerView.setAdapter(artistAdapter);
-        libraryViewModel.getArtistSample().observe(getViewLifecycleOwner(), artists -> {
+        libraryViewModel.getArtistSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), artists -> {
             if (artists == null) {
                 if (bind != null) bind.libraryArtistPlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.libraryArtistSector.setVisibility(View.GONE);
@@ -195,7 +195,7 @@ public class LibraryFragment extends Fragment {
             activity.navController.navigate(R.id.action_libraryFragment_to_songListPageFragment, bundle);
         });
         bind.genreRecyclerView.setAdapter(genreAdapter);
-        libraryViewModel.getGenreSample().observe(getViewLifecycleOwner(), genres -> {
+        libraryViewModel.getGenreSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), genres -> {
             if (genres == null) {
                 if (bind != null) bind.libraryGenrePlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.libraryGenresSector.setVisibility(View.GONE);
@@ -217,7 +217,7 @@ public class LibraryFragment extends Fragment {
 
         playlistHorizontalAdapter = new PlaylistHorizontalAdapter(activity, requireContext());
         bind.playlistRecyclerView.setAdapter(playlistHorizontalAdapter);
-        libraryViewModel.getPlaylistSample().observe(getViewLifecycleOwner(), playlists -> {
+        libraryViewModel.getPlaylistSample(getViewLifecycleOwner()).observe(getViewLifecycleOwner(), playlists -> {
             if (playlists == null) {
                 if (bind != null) bind.libraryPlaylistPlaceholder.placeholder.setVisibility(View.VISIBLE);
                 if (bind != null) bind.libraryPlaylistSector.setVisibility(View.GONE);

app/src/main/java/com/cappielloantonio/play/viewmodel/HomeViewModel.java

@@ -56,67 +56,98 @@ public class HomeViewModel extends AndroidViewModel {
         artistRepository = new ArtistRepository(application);
         playlistRepository = new PlaylistRepository(application);
         podcastRepository = new PodcastRepository(application);
-
-        songRepository.getRandomSample(10, null, null).observeForever(dicoverSongSample::postValue);
-        songRepository.getStarredSongs(true, 10).observeForever(starredTracksSample::postValue);
-        artistRepository.getStarredArtists(true, 10).observeForever(starredArtistsSample::postValue);
     }
 
-    public LiveData<List<Media>> getDiscoverSongSample() {
+    public LiveData<List<Media>> getDiscoverSongSample(LifecycleOwner owner) {
+        if (dicoverSongSample.getValue() == null) {
+            songRepository.getRandomSample(10, null, null).observe(owner, dicoverSongSample::postValue);
+        }
+
         return dicoverSongSample;
     }
 
     public LiveData<List<Album>> getRecentlyReleasedAlbums(LifecycleOwner owner) {
-        int currentYear = Calendar.getInstance().get(Calendar.YEAR);
+        if (newReleasedAlbum.getValue() == null) {
+            int currentYear = Calendar.getInstance().get(Calendar.YEAR);
 
-        albumRepository.getAlbums("byYear", 500, currentYear, currentYear).observe(owner, albums -> {
+            albumRepository.getAlbums("byYear", 500, currentYear, currentYear).observe(owner, albums -> {
-            albums.sort(Comparator.comparing(Album::getCreated).reversed());
+                albums.sort(Comparator.comparing(Album::getCreated).reversed());
-            newReleasedAlbum.postValue(albums.subList(0, Math.min(20, albums.size())));
+                newReleasedAlbum.postValue(albums.subList(0, Math.min(20, albums.size())));
-        });
+            });
+        }
 
         return newReleasedAlbum;
     }
 
-    public LiveData<List<Media>> getStarredTracksSample() {
+    public LiveData<List<Media>> getStarredTracksSample(LifecycleOwner owner) {
+        if (starredTracksSample.getValue() == null) {
+            songRepository.getStarredSongs(true, 10).observe(owner, starredTracksSample::postValue);
+        }
+
         return starredTracksSample;
     }
 
-    public LiveData<List<Artist>> getStarredArtistsSample() {
+    public LiveData<List<Artist>> getStarredArtistsSample(LifecycleOwner owner) {
+        if (starredArtistsSample.getValue() == null) {
+            artistRepository.getStarredArtists(true, 10).observe(owner, starredArtistsSample::postValue);
+        }
+
         return starredArtistsSample;
     }
 
     public LiveData<List<Media>> getStarredTracks(LifecycleOwner owner) {
-        songRepository.getStarredSongs(true, 20).observe(owner, starredTracks::postValue);
+        if (starredTracks.getValue() == null) {
+            songRepository.getStarredSongs(true, 20).observe(owner, starredTracks::postValue);
+        }
+
         return starredTracks;
     }
 
     public LiveData<List<Album>> getStarredAlbums(LifecycleOwner owner) {
-        albumRepository.getStarredAlbums(true, 20).observe(owner, starredAlbums::postValue);
+        if (starredAlbums.getValue() == null) {
+            albumRepository.getStarredAlbums(true, 20).observe(owner, starredAlbums::postValue);
+        }
+
         return starredAlbums;
     }
 
     public LiveData<List<Artist>> getStarredArtists(LifecycleOwner owner) {
-        artistRepository.getStarredArtists(true, 20).observe(owner, starredArtists::postValue);
+        if (starredArtists.getValue() == null) {
+            artistRepository.getStarredArtists(true, 20).observe(owner, starredArtists::postValue);
+        }
+
         return starredArtists;
     }
 
     public LiveData<List<Integer>> getYearList(LifecycleOwner owner) {
-        albumRepository.getDecades().observe(owner, years::postValue);
+        if (years.getValue() == null) {
+            albumRepository.getDecades().observe(owner, years::postValue);
+        }
+
         return years;
     }
 
     public LiveData<List<Album>> getMostPlayedAlbums(LifecycleOwner owner) {
-        albumRepository.getAlbums("frequent", 20, null, null).observe(owner, mostPlayedAlbumSample::postValue);
+        if (mostPlayedAlbumSample.getValue() == null) {
+            albumRepository.getAlbums("frequent", 20, null, null).observe(owner, mostPlayedAlbumSample::postValue);
+        }
+
         return mostPlayedAlbumSample;
     }
 
     public LiveData<List<Album>> getMostRecentlyAddedAlbums(LifecycleOwner owner) {
-        albumRepository.getAlbums("newest", 20, null, null).observe(owner, recentlyAddedAlbumSample::postValue);
+        if (recentlyAddedAlbumSample.getValue() == null) {
+            albumRepository.getAlbums("newest", 20, null, null).observe(owner, recentlyAddedAlbumSample::postValue);
+        }
+
         return recentlyAddedAlbumSample;
     }
 
     public LiveData<List<Album>> getRecentlyPlayedAlbumList(LifecycleOwner owner) {
-        albumRepository.getAlbums("recent", 20, null, null).observe(owner, recentlyPlayedAlbumSample::postValue);
+        if (recentlyPlayedAlbumSample.getValue() == null) {
+            albumRepository.getAlbums("recent", 20, null, null).observe(owner, recentlyPlayedAlbumSample::postValue);
+        }
+
         return recentlyPlayedAlbumSample;
     }
 
@@ -126,6 +157,7 @@ public class HomeViewModel extends AndroidViewModel {
             List<Playlist> subPlaylist = playlists.subList(0, Math.min(maxNumber, playlists.size()));
             pinnedPlaylists.postValue(subPlaylist);
         });
+
         return pinnedPlaylists;
     }
 
@@ -134,7 +166,10 @@ public class HomeViewModel extends AndroidViewModel {
     }
 
     public LiveData<List<Media>> getNewestPodcastEpisodes(LifecycleOwner owner) {
-        podcastRepository.getNewestPodcastEpisodes(20).observe(owner, newestPodcastEpisodes::postValue);
+        if (newestPodcastEpisodes.getValue() == null) {
+            podcastRepository.getNewestPodcastEpisodes(20).observe(owner, newestPodcastEpisodes::postValue);
+        }
+
         return newestPodcastEpisodes;
     }
 

app/src/main/java/com/cappielloantonio/play/viewmodel/LibraryViewModel.java

@@ -17,8 +17,6 @@ import com.cappielloantonio.play.repository.ArtistRepository;
 import com.cappielloantonio.play.repository.GenreRepository;
 import com.cappielloantonio.play.repository.PlaylistRepository;
 
-import java.util.Calendar;
-import java.util.Comparator;
 import java.util.List;
 
 public class LibraryViewModel extends AndroidViewModel {
@@ -41,28 +39,37 @@ public class LibraryViewModel extends AndroidViewModel {
         artistRepository = new ArtistRepository(application);
         genreRepository = new GenreRepository(application);
         playlistRepository = new PlaylistRepository(application);
-
-        // Inizializzate all'interno del costruttore, in modo da rimanere immutabili per tutto il
-        // ciclo di vita dell'applicazione
-        albumRepository.getAlbums("random", 10, null, null).observeForever(sampleAlbum::postValue);
-        artistRepository.getArtists(true, 10).observeForever(sampleArtist::postValue);
-        genreRepository.getGenres(true, 15).observeForever(sampleGenres::postValue);
-        playlistRepository.getPlaylists(true, 10).observeForever(playlistSample::postValue);
     }
 
-    public LiveData<List<Album>> getAlbumSample() {
+    public LiveData<List<Album>> getAlbumSample(LifecycleOwner owner) {
+        if (sampleAlbum.getValue() == null) {
+            albumRepository.getAlbums("random", 10, null, null).observe(owner, sampleAlbum::postValue);
+        }
+
         return sampleAlbum;
     }
 
-    public LiveData<List<Artist>> getArtistSample() {
+    public LiveData<List<Artist>> getArtistSample(LifecycleOwner owner) {
+        if (sampleArtist.getValue() == null) {
+            artistRepository.getArtists(true, 10).observe(owner, sampleArtist::postValue);
+        }
+
         return sampleArtist;
     }
 
-    public LiveData<List<Genre>> getGenreSample() {
+    public LiveData<List<Genre>> getGenreSample(LifecycleOwner owner) {
+        if (sampleGenres.getValue() == null) {
+            genreRepository.getGenres(true, 15).observe(owner, sampleGenres::postValue);
+        }
+
         return sampleGenres;
     }
 
-    public LiveData<List<Playlist>> getPlaylistSample() {
+    public LiveData<List<Playlist>> getPlaylistSample(LifecycleOwner owner) {
+        if (playlistSample.getValue() == null) {
+            playlistRepository.getPlaylists(true, 10).observe(owner, playlistSample::postValue);
+        }
+
         return playlistSample;
     }
 

app/src/main/java/com/cappielloantonio/play/viewmodel/PlaylistChooserViewModel.java

@@ -4,11 +4,12 @@ import android.app.Application;
 
 import androidx.annotation.NonNull;
 import androidx.lifecycle.AndroidViewModel;
+import androidx.lifecycle.LifecycleOwner;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 
-import com.cappielloantonio.play.model.Playlist;
 import com.cappielloantonio.play.model.Media;
+import com.cappielloantonio.play.model.Playlist;
 import com.cappielloantonio.play.repository.PlaylistRepository;
 
 import java.util.ArrayList;
@@ -25,12 +26,10 @@ public class PlaylistChooserViewModel extends AndroidViewModel {
         super(application);
 
         playlistRepository = new PlaylistRepository(application);
-
-        playlistRepository.getPlaylists(false, -1).observeForever(playlists::postValue);
-
     }
 
-    public LiveData<List<Playlist>> getPlaylistList() {
+    public LiveData<List<Playlist>> getPlaylistList(LifecycleOwner owner) {
+        playlistRepository.getPlaylists(false, -1).observe(owner, playlists::postValue);
         return playlists;
     }