Add sorting to LibraryFragment

Add basic sorting to LibraryFragment.

AuxioTODO

@@ -5,7 +5,6 @@ TODO:
 
 /detail/
 
-- Add genre detail
 - ? Implement Toolbar update functionality ?
 - ! Implement shared element transitions !
 
@@ -24,11 +23,14 @@ TODO:
 
 /library/
 
-- ? Move into ViewPager ?
+- Re-add albums/genres into a single adapter
-- Sorting
+- Add highlighting to the current sortmode
 - Search
-    - ? Show Artists, Albums, and Songs in search ?
 - Exit functionality
+- ? Show Artists, Albums, and Songs in search ?
+- ? Move into ViewPager ?
+- ! Move Adapter functionality to ListAdapter!
+
 
 To be added:
 /prefs/

app/src/main/java/org/oxycblt/auxio/detail/AlbumDetailFragment.kt

@@ -15,7 +15,6 @@ import org.oxycblt.auxio.databinding.FragmentAlbumDetailBinding
 import org.oxycblt.auxio.detail.adapters.DetailSongAdapter
 import org.oxycblt.auxio.music.MusicViewModel
 import org.oxycblt.auxio.recycler.ClickListener
-import org.oxycblt.auxio.recycler.SortMode
 import org.oxycblt.auxio.theme.applyDivider
 import org.oxycblt.auxio.theme.toColor
 
@@ -65,7 +64,7 @@ class AlbumDetailFragment : Fragment() {
 
         // If the album was shown directly from LibraryFragment, Then enable the ability to
         // navigate upwards to the parent artist
-        if (args.fromLibrary) {
+        if (args.enableParentNav) {
             detailModel.navToParent.observe(viewLifecycleOwner) {
                 if (it) {
                     findNavController().navigate(
@@ -89,14 +88,7 @@ class AlbumDetailFragment : Fragment() {
 
             // Then update the sort mode of the album adapter.
             songAdapter.submitList(
-                detailModel.currentAlbum.value!!.songs.sortedWith(
+                mode.getSortedSongList(detailModel.currentAlbum.value!!.songs)
-                    SortMode.songSortComparators.getOrDefault(
-                        mode,
-
-                        // If any invalid value is given, just default to the normal sort order.
-                        compareByDescending { it.track }
-                    )
-                )
             )
         }
 

app/src/main/java/org/oxycblt/auxio/detail/ArtistDetailFragment.kt

@@ -16,7 +16,6 @@ import org.oxycblt.auxio.detail.adapters.DetailAlbumAdapter
 import org.oxycblt.auxio.music.Album
 import org.oxycblt.auxio.music.MusicViewModel
 import org.oxycblt.auxio.recycler.ClickListener
-import org.oxycblt.auxio.recycler.SortMode
 import org.oxycblt.auxio.theme.applyDivider
 import org.oxycblt.auxio.theme.toColor
 
@@ -72,14 +71,7 @@ class ArtistDetailFragment : Fragment() {
 
             // Then update the sort mode of the album adapter.
             albumAdapter.submitList(
-                detailModel.currentArtist.value!!.albums.sortedWith(
+                mode.getSortedAlbumList(detailModel.currentArtist.value!!.albums)
-                    SortMode.albumSortComparators.getOrDefault(
-                        mode,
-
-                        // If any invalid value is given, just default to the normal sort order.
-                        compareByDescending { it.year }
-                    )
-                )
             )
         }
 

app/src/main/java/org/oxycblt/auxio/detail/GenreDetailFragment.kt

@@ -16,7 +16,6 @@ import org.oxycblt.auxio.detail.adapters.DetailArtistAdapter
 import org.oxycblt.auxio.music.Artist
 import org.oxycblt.auxio.music.MusicViewModel
 import org.oxycblt.auxio.recycler.ClickListener
-import org.oxycblt.auxio.recycler.SortMode
 import org.oxycblt.auxio.theme.applyDivider
 import org.oxycblt.auxio.theme.toColor
 
@@ -70,14 +69,7 @@ class GenreDetailFragment : Fragment() {
 
             // Then update the sort mode of the artist adapter.
             albumAdapter.submitList(
-                detailModel.currentGenre.value!!.artists.sortedWith(
+                mode.getSortedArtistList(detailModel.currentGenre.value!!.artists)
-                    SortMode.artistSortComparators.getOrDefault(
-                        mode,
-
-                        // If any invalid value is given, just default to the normal sort order.
-                        compareByDescending { it.name }
-                    )
-                )
             )
         }
 

app/src/main/java/org/oxycblt/auxio/library/LibraryFragment.kt

@@ -5,29 +5,24 @@ import android.util.Log
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import androidx.core.content.ContextCompat
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.activityViewModels
 import androidx.navigation.fragment.findNavController
 import org.oxycblt.auxio.MainFragmentDirections
+import org.oxycblt.auxio.R
 import org.oxycblt.auxio.databinding.FragmentLibraryBinding
-import org.oxycblt.auxio.library.adapters.AlbumAdapter
 import org.oxycblt.auxio.library.adapters.ArtistAdapter
-import org.oxycblt.auxio.library.adapters.GenreAdapter
 import org.oxycblt.auxio.music.Album
 import org.oxycblt.auxio.music.Artist
+import org.oxycblt.auxio.music.BaseModel
 import org.oxycblt.auxio.music.Genre
 import org.oxycblt.auxio.music.MusicViewModel
 import org.oxycblt.auxio.recycler.ClickListener
-import org.oxycblt.auxio.theme.SHOW_ALBUMS
-import org.oxycblt.auxio.theme.SHOW_ARTISTS
-import org.oxycblt.auxio.theme.SHOW_GENRES
 import org.oxycblt.auxio.theme.applyDivider
 
 class LibraryFragment : Fragment() {
 
-    // FIXME: Temp value, remove when there are actual preferences
-    private val libraryMode = SHOW_ARTISTS
-
     private val musicModel: MusicViewModel by activityViewModels()
     private val libraryModel: LibraryViewModel by activityViewModels()
 
@@ -38,34 +33,34 @@ class LibraryFragment : Fragment() {
     ): View? {
         val binding = FragmentLibraryBinding.inflate(inflater)
 
-        binding.libraryRecycler.adapter = when (libraryMode) {
+        val artistAdapter = ArtistAdapter(
-            SHOW_ARTISTS -> ArtistAdapter(
+            ClickListener { navToItem(it) }
-                musicModel.artists.value!!,
+        )
-                ClickListener {
-                    navToArtist(it)
-                }
-            )
-
-            SHOW_ALBUMS -> AlbumAdapter(
-                musicModel.albums.value!!,
-                ClickListener {
-                    navToAlbum(it)
-                }
-            )
-
-            SHOW_GENRES -> GenreAdapter(
-                musicModel.genres.value!!,
-                ClickListener {
-                    navToGenre(it)
-                }
-            )
-
-            else -> null
-        }
 
+        binding.libraryRecycler.adapter = artistAdapter
         binding.libraryRecycler.applyDivider()
         binding.libraryRecycler.setHasFixedSize(true)
 
+        libraryModel.sortMode.observe(viewLifecycleOwner) { mode ->
+            binding.libraryToolbar.overflowIcon = ContextCompat.getDrawable(
+                requireContext(), mode.iconRes
+            )
+
+            artistAdapter.updateData(
+                mode.getSortedArtistList(
+                    musicModel.artists.value!!
+                )
+            )
+        }
+
+        binding.libraryToolbar.setOnMenuItemClickListener {
+            libraryModel.updateSortMode(it)
+
+            true
+        }
+
+        binding.libraryToolbar.inflateMenu(R.menu.menu_library)
+
         Log.d(this::class.simpleName, "Fragment created.")
 
         return binding.root
@@ -77,39 +72,19 @@ class LibraryFragment : Fragment() {
         libraryModel.isAlreadyNavigating = false
     }
 
-    private fun navToArtist(artist: Artist) {
+    private fun navToItem(baseModel: BaseModel) {
-        // Dont navigate if an item has already been selected
+        // Don't navigate if an item has already been selected
         if (!libraryModel.isAlreadyNavigating) {
             libraryModel.isAlreadyNavigating = true
 
             findNavController().navigate(
-                MainFragmentDirections.actionShowArtist(
+                when (baseModel) {
-                    artist.id
+                    is Genre -> MainFragmentDirections.actionShowGenre(baseModel.id)
-                )
+                    is Artist -> MainFragmentDirections.actionShowArtist(baseModel.id)
-            )
+                    is Album -> MainFragmentDirections.actionShowAlbum(baseModel.id, true)
-        }
-    }
 
-    private fun navToAlbum(album: Album) {
+                    else -> return
-        if (!libraryModel.isAlreadyNavigating) {
+                }
-            libraryModel.isAlreadyNavigating = true
-
-            findNavController().navigate(
-                MainFragmentDirections.actionShowAlbum(
-                    album.id, true
-                )
-            )
-        }
-    }
-
-    private fun navToGenre(genre: Genre) {
-        if (!libraryModel.isAlreadyNavigating) {
-            libraryModel.isAlreadyNavigating = true
-
-            findNavController().navigate(
-                MainFragmentDirections.actionShowGenre(
-                    genre.id
-                )
             )
         }
     }

app/src/main/java/org/oxycblt/auxio/library/LibraryViewModel.kt

@@ -1,7 +1,34 @@
 package org.oxycblt.auxio.library
 
+import android.view.MenuItem
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
+import org.oxycblt.auxio.R
+import org.oxycblt.auxio.recycler.SortMode
+import org.oxycblt.auxio.theme.SHOW_ARTISTS
 
 class LibraryViewModel : ViewModel() {
     var isAlreadyNavigating = false
+
+    // TODO: Move these to pref values when they're added
+    private val mShowMode = MutableLiveData(SHOW_ARTISTS)
+    val showMode: LiveData<Int> get() = mShowMode
+
+    private val mSortMode = MutableLiveData(SortMode.ALPHA_UP)
+    val sortMode: LiveData<SortMode> get() = mSortMode
+
+    fun updateSortMode(item: MenuItem) {
+        val mode = when (item.itemId) {
+            R.id.sort_none -> SortMode.NONE
+            R.id.sort_alpha_down -> SortMode.ALPHA_DOWN
+            R.id.sort_alpha_up -> SortMode.ALPHA_UP
+
+            else -> SortMode.NONE
+        }
+
+        if (mode != mSortMode.value) {
+            mSortMode.value = mode
+        }
+    }
 }

app/src/main/java/org/oxycblt/auxio/library/adapters/AlbumAdapter.kt

@@ -2,18 +2,16 @@ package org.oxycblt.auxio.library.adapters
 
 import android.view.LayoutInflater
 import android.view.ViewGroup
-import androidx.recyclerview.widget.RecyclerView
+import androidx.recyclerview.widget.ListAdapter
 import org.oxycblt.auxio.databinding.ItemAlbumBinding
 import org.oxycblt.auxio.music.Album
 import org.oxycblt.auxio.recycler.BaseViewHolder
 import org.oxycblt.auxio.recycler.ClickListener
+import org.oxycblt.auxio.recycler.DiffCallback
 
 class AlbumAdapter(
-    private val data: List<Album>,
     private val listener: ClickListener<Album>
-) : RecyclerView.Adapter<AlbumAdapter.ViewHolder>() {
+) : ListAdapter<Album, AlbumAdapter.ViewHolder>(DiffCallback()) {
-
-    override fun getItemCount(): Int = data.size
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
         return ViewHolder(
@@ -22,7 +20,7 @@ class AlbumAdapter(
     }
 
     override fun onBindViewHolder(holder: ViewHolder, position: Int) {
-        holder.bind(data[position])
+        holder.bind(getItem(position))
     }
 
     inner class ViewHolder(

app/src/main/java/org/oxycblt/auxio/library/adapters/ArtistAdapter.kt

@@ -9,10 +9,11 @@ import org.oxycblt.auxio.recycler.BaseViewHolder
 import org.oxycblt.auxio.recycler.ClickListener
 
 class ArtistAdapter(
-    private val data: List<Artist>,
     private val listener: ClickListener<Artist>
 ) : RecyclerView.Adapter<ArtistAdapter.ViewHolder>() {
 
+    private var data = listOf<Artist>()
+
     override fun getItemCount(): Int = data.size
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
@@ -25,6 +26,12 @@ class ArtistAdapter(
         holder.bind(data[position])
     }
 
+    fun updateData(newData: List<Artist>) {
+        data = newData
+
+        notifyDataSetChanged()
+    }
+
     inner class ViewHolder(
         private val binding: ItemArtistBinding
     ) : BaseViewHolder<Artist>(binding, listener) {

app/src/main/java/org/oxycblt/auxio/library/adapters/GenreAdapter.kt

@@ -2,18 +2,16 @@ package org.oxycblt.auxio.library.adapters
 
 import android.view.LayoutInflater
 import android.view.ViewGroup
-import androidx.recyclerview.widget.RecyclerView
+import androidx.recyclerview.widget.ListAdapter
 import org.oxycblt.auxio.databinding.ItemGenreBinding
 import org.oxycblt.auxio.music.Genre
 import org.oxycblt.auxio.recycler.BaseViewHolder
 import org.oxycblt.auxio.recycler.ClickListener
+import org.oxycblt.auxio.recycler.DiffCallback
 
 class GenreAdapter(
-    private val data: List<Genre>,
     private val listener: ClickListener<Genre>
-) : RecyclerView.Adapter<GenreAdapter.ViewHolder>() {
+) : ListAdapter<Genre, GenreAdapter.ViewHolder>(DiffCallback()) {
-
-    override fun getItemCount(): Int = data.size
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
         return ViewHolder(
@@ -22,7 +20,7 @@ class GenreAdapter(
     }
 
     override fun onBindViewHolder(holder: ViewHolder, position: Int) {
-        holder.bind(data[position])
+        holder.bind(getItem(position))
     }
 
     inner class ViewHolder(

app/src/main/java/org/oxycblt/auxio/music/processing/MusicSorter.kt

@@ -21,7 +21,11 @@ class MusicSorter(
         sortAlbumsIntoArtists()
         sortArtistsIntoGenres()
 
-        finalizeMusic()
+        // Remove genre duplicates at the end, as duplicate genres can be added during
+        // the sorting process as well.
+        genres = genres.distinctBy {
+            it.name
+        }.toMutableList()
     }
 
     private fun sortSongsIntoAlbums() {
@@ -155,25 +159,4 @@ class MusicSorter(
             )
         }
     }
-
-    // Finalize music
-    private fun finalizeMusic() {
-        // Remove genre duplicates now, as duplicate genres can be added during the sorting process.
-        genres = genres.distinctBy {
-            it.name
-        }.toMutableList()
-
-        // Then finally sort the music
-        genres.sortWith(
-            compareBy(String.CASE_INSENSITIVE_ORDER, { it.name })
-        )
-
-        artists.sortWith(
-            compareBy(String.CASE_INSENSITIVE_ORDER, { it.name })
-        )
-
-        albums.sortWith(
-            compareBy(String.CASE_INSENSITIVE_ORDER, { it.name })
-        )
-    }
 }

app/src/main/java/org/oxycblt/auxio/recycler/RecyclerUtils.kt

@@ -3,11 +3,7 @@ package org.oxycblt.auxio.recycler
 import androidx.databinding.ViewDataBinding
 import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.RecyclerView
-import org.oxycblt.auxio.R
-import org.oxycblt.auxio.music.Album
-import org.oxycblt.auxio.music.Artist
 import org.oxycblt.auxio.music.BaseModel
-import org.oxycblt.auxio.music.Song
 
 // RecyclerView click listener
 class ClickListener<T>(val onClick: (T) -> Unit)
@@ -44,44 +40,3 @@ abstract class BaseViewHolder<T : BaseModel>(
 
     abstract fun onBind(model: T)
 }
-
-// Sorting modes
-enum class SortMode(val iconRes: Int) {
-    // Icons for each mode are assigned to the enums themselves
-    NONE(R.drawable.ic_sort_alpha_down),
-    ALPHA_UP(R.drawable.ic_sort_alpha_up),
-    ALPHA_DOWN(R.drawable.ic_sort_alpha_down),
-    NUMERIC_UP(R.drawable.ic_sort_numeric_up),
-    NUMERIC_DOWN(R.drawable.ic_sort_numeric_down);
-
-    companion object {
-        // Sort comparators are different for each music model, so they are static maps instead.
-        val songSortComparators = mapOf<SortMode, Comparator<Song>>(
-            NUMERIC_DOWN to compareBy { it.track },
-            NUMERIC_UP to compareByDescending { it.track }
-        )
-
-        val albumSortComparators = mapOf<SortMode, Comparator<Album>>(
-            NUMERIC_DOWN to compareByDescending { it.year },
-            NUMERIC_UP to compareBy { it.year },
-
-            // Alphabetic sorting needs to be case-insensitive
-            ALPHA_DOWN to compareByDescending(
-                String.CASE_INSENSITIVE_ORDER
-            ) { it.name },
-            ALPHA_UP to compareBy(
-                String.CASE_INSENSITIVE_ORDER
-            ) { it.name }
-        )
-
-        val artistSortComparators = mapOf<SortMode, Comparator<Artist>>(
-            // Alphabetic sorting needs to be case-insensitive
-            ALPHA_DOWN to compareBy(
-                String.CASE_INSENSITIVE_ORDER
-            ) { it.name },
-            ALPHA_UP to compareByDescending(
-                String.CASE_INSENSITIVE_ORDER
-            ) { it.name }
-        )
-    }
-}

app/src/main/java/org/oxycblt/auxio/recycler/SortMode.kt

@@ -0,0 +1,89 @@
+package org.oxycblt.auxio.recycler
+
+import org.oxycblt.auxio.R
+import org.oxycblt.auxio.music.Album
+import org.oxycblt.auxio.music.Artist
+import org.oxycblt.auxio.music.Genre
+import org.oxycblt.auxio.music.Song
+
+// Sorting modes
+enum class SortMode(val iconRes: Int) {
+    // Icons for each mode are assigned to the enums themselves
+    NONE(R.drawable.ic_sort_none),
+    ALPHA_UP(R.drawable.ic_sort_alpha_up),
+    ALPHA_DOWN(R.drawable.ic_sort_alpha_down),
+    NUMERIC_UP(R.drawable.ic_sort_numeric_up),
+    NUMERIC_DOWN(R.drawable.ic_sort_numeric_down);
+
+    fun getSortedGenreList(list: List<Genre>): List<Genre> {
+        return when (this) {
+            ALPHA_UP -> list.sortedWith(
+                compareByDescending(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            ALPHA_DOWN -> list.sortedWith(
+                compareBy(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            else -> list
+        }
+    }
+
+    fun getSortedArtistList(list: List<Artist>): List<Artist> {
+        return when (this) {
+            ALPHA_UP -> list.sortedWith(
+                compareByDescending(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            ALPHA_DOWN -> list.sortedWith(
+                compareBy(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            else -> list
+        }
+    }
+
+    fun getSortedAlbumList(list: List<Album>): List<Album> {
+        return when (this) {
+            ALPHA_UP -> list.sortedWith(
+                compareByDescending(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            ALPHA_DOWN -> list.sortedWith(
+                compareBy(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            NUMERIC_UP -> list.sortedBy { it.year }
+            NUMERIC_DOWN -> list.sortedByDescending { it.year }
+
+            else -> list
+        }
+    }
+
+    fun getSortedSongList(list: List<Song>): List<Song> {
+        return when (this) {
+            ALPHA_UP -> list.sortedWith(
+                compareByDescending(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            ALPHA_DOWN -> list.sortedWith(
+                compareBy(String.CASE_INSENSITIVE_ORDER) { it.name }
+            )
+
+            NUMERIC_UP -> list.sortedWith(compareByDescending { it.track })
+            NUMERIC_DOWN -> list.sortedWith(compareBy { it.track })
+
+            else -> list
+        }
+    }
+
+    fun toMenuId(): Int {
+        return when (this) {
+            NONE -> R.id.sort_none
+            ALPHA_UP -> R.id.sort_alpha_up
+            ALPHA_DOWN -> R.id.sort_alpha_down
+
+            else -> R.id.sort_none
+        }
+    }
+}

app/src/main/res/drawable/ic_sort_none.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorPrimary">
+  <path
+      android:fillColor="@android:color/white"
+      android:pathData="M3,18h6v-2L3,16v2zM3,6v2h18L21,6L3,6zM3,13h12v-2L3,11v2z"/>
+</vector>

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

@@ -7,7 +7,8 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:orientation="vertical"
-        android:animateLayoutChanges="true">
+        android:animateLayoutChanges="true"
+        android:descendantFocusability="blocksDescendants">
 
         <androidx.appcompat.widget.Toolbar
             android:id="@+id/library_toolbar"

app/src/main/res/menu/menu_library.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android">
+    <item
+        android:id="@+id/sort_none"
+        android:icon="@drawable/ic_sort_none"
+        android:title="@string/label_sort_none"
+        android:contentDescription="@string/description_sort_none"/>
+    <item
+        android:id="@+id/sort_alpha_down"
+        android:icon="@drawable/ic_sort_alpha_down"
+        android:title="@string/label_sort_alpha_down"
+        android:contentDescription="@string/description_sort_alpha_down"/>
+    <item
+        android:id="@+id/sort_alpha_up"
+        android:icon="@drawable/ic_sort_alpha_up"
+        android:title="@string/label_sort_alpha_up"
+        android:contentDescription="@string/description_sort_alpha_up"/>
+</menu>

app/src/main/res/navigation/nav_main.xml

@@ -73,7 +73,7 @@
             android:name="albumId"
             app:argType="long" />
         <argument
-            android:name="fromLibrary"
+            android:name="enableParentNav"
             app:argType="boolean" />
         <action
             android:id="@+id/action_show_parent_artist"

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

@@ -2,35 +2,48 @@
 <resources>
     <string name="app_name">Auxio</string>
 
+    <!-- Title Namespace | Toolbar titles -->
     <string name="title_library_fragment">Library</string>
     <string name="title_all_songs">All Songs</string>
 
+    <!-- Error Namespace | Error Labels -->
     <string name="error_no_music">No music found.</string>
     <string name="error_music_load_failed">Music loading failed.</string>
     <string name="error_no_perms">Permissions to read storage are needed.</string>
 
+    <!-- Label Namespace | Static Labels -->
     <string name="label_retry">Retry</string>
     <string name="label_grant">Grant</string>
     <string name="label_artists">Artists</string>
     <string name="label_albums">Albums</string>
     <string name="label_songs">Songs</string>
+    <string name="label_sort_none">Default</string>
+    <string name="label_sort_alpha_down">A-Z</string>
+    <string name="label_sort_alpha_up">Z-A</string>
 
+    <!-- Description Namespace | Accessibility Strings -->
     <string name="description_album_cover">Album Cover for %s</string>
     <string name="description_artist_image">Artist Image for %s</string>
     <string name="description_genre_image">Genre Image for %s</string>
     <string name="description_track_number">Track %s</string>
     <string name="description_error">Error</string>
     <string name="description_sort_button">Change Sorting Mode</string>
+    <string name="description_sort_none">Default Sort Order</string>
+    <string name="description_sort_alpha_down">Sort from A to Z</string>
+    <string name="description_sort_alpha_up">Sort from Z to A</string>
 
+    <!-- Placeholder Namespace | Placeholder values -->
     <string name="placeholder_genre">Unknown Genre</string>
     <string name="placeholder_artist">Unknown Artist</string>
     <string name="placeholder_album">Unknown Album</string>
     <string name="placeholder_no_date">No Date</string>
 
+    <!-- Format Namespace | Value formatting -->
     <string name="format_info">%1$s / %2$s</string>
     <string name="format_double_info">%1$s / %2$s / %3$s</string>
     <string name="format_double_counts">%1$s, %2$s</string>
 
+    <!-- Format Namespace | Value formatting with plurals -->
     <plurals name="format_song_count">
         <item quantity="one">%s Song</item>
         <item quantity="other">%s Songs</item>