list: rework diffing abstraction

Make all adapters relying on diffing unified into a DiffAdapter
superclass that can then accurately respond to the new
UpdateInstructions data.

UpdateInstructions is still not fully used everywhere, but will be
soon.

CHANGELOG.md

@@ -9,6 +9,7 @@
 - Added ability to edit previously played or currently playing items in the queue
 - Added support for date values formatted as "YYYYMMDD"
 - Pressing the button will now clear the current selection before navigating back
+- Added support for non-standard `ARTISTS` tags
 
 #### What's Fixed
 - Fixed unreliable ReplayGain adjustment application in certain situations

app/src/main/AndroidManifest.xml

@@ -21,7 +21,7 @@
     <queries />
 
     <application
-        android:name=".AuxioApp"
+        android:name=".Auxio"
         android:allowBackup="true"
         android:fullBackupContent="@xml/backup_descriptor"
         android:icon="@mipmap/ic_launcher"

app/src/main/java/org/oxycblt/auxio/Auxio.kt

@@ -38,7 +38,7 @@ import org.oxycblt.auxio.ui.UISettings
  * Auxio: A simple, rational music player for android.
  * @author Alexander Capehart (OxygenCobalt)
  */
-class AuxioApp : Application(), ImageLoaderFactory {
+class Auxio : Application(), ImageLoaderFactory {
     override fun onCreate() {
         super.onCreate()
         // Migrate any settings that may have changed in an app update.

app/src/main/java/org/oxycblt/auxio/MainActivity.kt

@@ -131,7 +131,7 @@ class MainActivity : AppCompatActivity() {
         val action =
             when (intent.action) {
                 Intent.ACTION_VIEW -> InternalPlayer.Action.Open(intent.data ?: return false)
-                AuxioApp.INTENT_KEY_SHORTCUT_SHUFFLE -> InternalPlayer.Action.ShuffleAll
+                Auxio.INTENT_KEY_SHORTCUT_SHUFFLE -> InternalPlayer.Action.ShuffleAll
                 else -> return false
             }
         playbackModel.startAction(action)

app/src/main/java/org/oxycblt/auxio/MainFragment.kt

@@ -235,8 +235,8 @@ class MainFragment :
             tryHideAllSheets()
         }
 
-        // Since the listener is also reliant on the bottom sheets, we must also update it
+        // Since the navigation listener is also reliant on the bottom sheets, we must also update
-        // every frame.
+        // it every frame.
         callback.invalidateEnabled()
 
         return true

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

@@ -82,7 +82,7 @@ class AlbumDetailFragment :
         // DetailViewModel handles most initialization from the navigation argument.
         detailModel.setAlbumUid(args.albumUid)
         collectImmediately(detailModel.currentAlbum, ::updateAlbum)
-        collectImmediately(detailModel.albumList, detailAdapter::submitList)
+        collectImmediately(detailModel.albumList, detailAdapter::diffList)
         collectImmediately(
             playbackModel.song, playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
         collect(navModel.exploreNavigationItem, ::handleNavigation)
@@ -170,10 +170,10 @@ class AlbumDetailFragment :
 
     private fun updatePlayback(song: Song?, parent: MusicParent?, isPlaying: Boolean) {
         if (parent is Album && parent == unlikelyToBeNull(detailModel.currentAlbum.value)) {
-            detailAdapter.setPlayingItem(song, isPlaying)
+            detailAdapter.setPlaying(song, isPlaying)
         } else {
             // Clear the ViewHolders if the mode isn't ALL_SONGS
-            detailAdapter.setPlayingItem(null, isPlaying)
+            detailAdapter.setPlaying(null, isPlaying)
         }
     }
 
@@ -258,7 +258,7 @@ class AlbumDetailFragment :
     }
 
     private fun updateSelection(selected: List<Music>) {
-        detailAdapter.setSelectedItems(selected)
+        detailAdapter.setSelected(selected.toSet())
         requireBinding().detailSelectionToolbar.updateSelectionAmount(selected.size)
     }
 }

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

@@ -85,7 +85,7 @@ class ArtistDetailFragment :
         // DetailViewModel handles most initialization from the navigation argument.
         detailModel.setArtistUid(args.artistUid)
         collectImmediately(detailModel.currentArtist, ::updateItem)
-        collectImmediately(detailModel.artistList, detailAdapter::submitList)
+        collectImmediately(detailModel.artistList, detailAdapter::diffList)
         collectImmediately(
             playbackModel.song, playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
         collect(navModel.exploreNavigationItem, ::handleNavigation)
@@ -195,7 +195,7 @@ class ArtistDetailFragment :
                 else -> null
             }
 
-        detailAdapter.setPlayingItem(playingItem, isPlaying)
+        detailAdapter.setPlaying(playingItem, isPlaying)
     }
 
     private fun handleNavigation(item: Music?) {
@@ -234,7 +234,7 @@ class ArtistDetailFragment :
     }
 
     private fun updateSelection(selected: List<Music>) {
-        detailAdapter.setSelectedItems(selected)
+        detailAdapter.setSelected(selected.toSet())
         requireBinding().detailSelectionToolbar.updateSelectionAmount(selected.size)
     }
 }

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

@@ -84,7 +84,7 @@ class GenreDetailFragment :
         // DetailViewModel handles most initialization from the navigation argument.
         detailModel.setGenreUid(args.genreUid)
         collectImmediately(detailModel.currentGenre, ::updateItem)
-        collectImmediately(detailModel.genreList, detailAdapter::submitList)
+        collectImmediately(detailModel.genreList, detailAdapter::diffList)
         collectImmediately(
             playbackModel.song, playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
         collect(navModel.exploreNavigationItem, ::handleNavigation)
@@ -189,7 +189,7 @@ class GenreDetailFragment :
         if (parent is Genre && parent.uid == unlikelyToBeNull(detailModel.currentGenre.value).uid) {
             playingMusic = song
         }
-        detailAdapter.setPlayingItem(playingMusic, isPlaying)
+        detailAdapter.setPlaying(playingMusic, isPlaying)
     }
 
     private fun handleNavigation(item: Music?) {
@@ -217,7 +217,7 @@ class GenreDetailFragment :
     }
 
     private fun updateSelection(selected: List<Music>) {
-        detailAdapter.setSelectedItems(selected)
+        detailAdapter.setSelected(selected.toSet())
         requireBinding().detailSelectionToolbar.updateSelectionAmount(selected.size)
     }
 }

app/src/main/java/org/oxycblt/auxio/detail/recycler/AlbumDetailAdapter.kt

@@ -57,7 +57,7 @@ class AlbumDetailAdapter(private val listener: Listener) : DetailAdapter(listene
     }
 
     override fun getItemViewType(position: Int) =
-        when (differ.currentList[position]) {
+        when (getItem(position)) {
             // Support the Album header, sub-headers for each disc, and special album songs.
             is Album -> AlbumDetailViewHolder.VIEW_TYPE
             is DiscHeader -> DiscHeaderViewHolder.VIEW_TYPE
@@ -75,7 +75,7 @@ class AlbumDetailAdapter(private val listener: Listener) : DetailAdapter(listene
 
     override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
         super.onBindViewHolder(holder, position)
-        when (val item = differ.currentList[position]) {
+        when (val item = getItem(position)) {
             is Album -> (holder as AlbumDetailViewHolder).bind(item, listener)
             is DiscHeader -> (holder as DiscHeaderViewHolder).bind(item)
             is Song -> (holder as AlbumSongViewHolder).bind(item, listener)
@@ -83,9 +83,12 @@ class AlbumDetailAdapter(private val listener: Listener) : DetailAdapter(listene
     }
 
     override fun isItemFullWidth(position: Int): Boolean {
+        if (super.isItemFullWidth(position)) {
+            return true
+        }
         // The album and disc headers should be full-width in all configurations.
-        val item = differ.currentList[position]
+        val item = getItem(position)
-        return super.isItemFullWidth(position) || item is Album || item is DiscHeader
+        return item is Album || item is DiscHeader
     }
 
     private companion object {

app/src/main/java/org/oxycblt/auxio/detail/recycler/ArtistDetailAdapter.kt

@@ -46,7 +46,7 @@ import org.oxycblt.auxio.util.inflater
 class ArtistDetailAdapter(private val listener: Listener<Music>) :
     DetailAdapter(listener, DIFF_CALLBACK) {
     override fun getItemViewType(position: Int) =
-        when (differ.currentList[position]) {
+        when (getItem(position)) {
             // Support an artist header, and special artist albums/songs.
             is Artist -> ArtistDetailViewHolder.VIEW_TYPE
             is Album -> ArtistAlbumViewHolder.VIEW_TYPE
@@ -65,7 +65,7 @@ class ArtistDetailAdapter(private val listener: Listener<Music>) :
     override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
         super.onBindViewHolder(holder, position)
         // Re-binding an item with new data and not just a changed selection/playing state.
-        when (val item = differ.currentList[position]) {
+        when (val item = getItem(position)) {
             is Artist -> (holder as ArtistDetailViewHolder).bind(item, listener)
             is Album -> (holder as ArtistAlbumViewHolder).bind(item, listener)
             is Song -> (holder as ArtistSongViewHolder).bind(item, listener)
@@ -73,9 +73,11 @@ class ArtistDetailAdapter(private val listener: Listener<Music>) :
     }
 
     override fun isItemFullWidth(position: Int): Boolean {
+        if (super.isItemFullWidth(position)) {
+            return true
+        }
         // Artist headers should be full-width in all configurations.
-        val item = differ.currentList[position]
+        return getItem(position) is Artist
-        return super.isItemFullWidth(position) || item is Artist
     }
 
     private companion object {

app/src/main/java/org/oxycblt/auxio/detail/recycler/DetailAdapter.kt

@@ -20,7 +20,6 @@ package org.oxycblt.auxio.detail.recycler
 import android.view.View
 import android.view.ViewGroup
 import androidx.appcompat.widget.TooltipCompat
-import androidx.recyclerview.widget.AsyncListDiffer
 import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.RecyclerView
 import org.oxycblt.auxio.IntegerTable
@@ -37,19 +36,19 @@ import org.oxycblt.auxio.util.inflater
 /**
  * A [RecyclerView.Adapter] that implements behavior shared across each detail view's adapters.
  * @param listener A [Listener] to bind interactions to.
- * @param itemCallback A [DiffUtil.ItemCallback] to use with [AsyncListDiffer] when updating the
+ * @param diffCallback A [DiffUtil.ItemCallback] to use for item comparison when diffing the
  * internal list.
  * @author Alexander Capehart (OxygenCobalt)
  */
 abstract class DetailAdapter(
     private val listener: Listener<*>,
-    itemCallback: DiffUtil.ItemCallback<Item>
+    diffCallback: DiffUtil.ItemCallback<Item>
-) : SelectionIndicatorAdapter<RecyclerView.ViewHolder>(), AuxioRecyclerView.SpanSizeLookup {
+) :
-    // Safe to leak this since the listener will not fire during initialization
+    SelectionIndicatorAdapter<Item, RecyclerView.ViewHolder>(ListDiffer.Async(diffCallback)),
-    @Suppress("LeakingThis") protected val differ = AsyncListDiffer(this, itemCallback)
+    AuxioRecyclerView.SpanSizeLookup {
 
     override fun getItemViewType(position: Int) =
-        when (differ.currentList[position]) {
+        when (getItem(position)) {
             // Implement support for headers and sort headers
             is Header -> HeaderViewHolder.VIEW_TYPE
             is SortHeader -> SortHeaderViewHolder.VIEW_TYPE
@@ -64,7 +63,7 @@ abstract class DetailAdapter(
         }
 
     override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
-        when (val item = differ.currentList[position]) {
+        when (val item = getItem(position)) {
             is Header -> (holder as HeaderViewHolder).bind(item)
             is SortHeader -> (holder as SortHeaderViewHolder).bind(item, listener)
         }
@@ -72,22 +71,10 @@ abstract class DetailAdapter(
 
     override fun isItemFullWidth(position: Int): Boolean {
         // Headers should be full-width in all configurations.
-        val item = differ.currentList[position]
+        val item = getItem(position)
         return item is Header || item is SortHeader
     }
 
-    override val currentList: List<Item>
-        get() = differ.currentList
-
-    /**
-     * Asynchronously update the list with new items. Assumes that the list only contains data
-     * supported by the concrete [DetailAdapter] implementation.
-     * @param newList The new [Item]s for the adapter to display.
-     */
-    fun submitList(newList: List<Item>) {
-        differ.submitList(newList)
-    }
-
     /** An extended [SelectableListListener] for [DetailAdapter] implementations. */
     interface Listener<in T : Music> : SelectableListListener<T> {
         // TODO: Split off into sub-listeners if a collapsing toolbar is implemented.

app/src/main/java/org/oxycblt/auxio/detail/recycler/GenreDetailAdapter.kt

@@ -44,7 +44,7 @@ import org.oxycblt.auxio.util.inflater
 class GenreDetailAdapter(private val listener: Listener<Music>) :
     DetailAdapter(listener, DIFF_CALLBACK) {
     override fun getItemViewType(position: Int) =
-        when (differ.currentList[position]) {
+        when (getItem(position)) {
             // Support the Genre header and generic Artist/Song items. There's nothing about
             // a genre that will make the artists/songs homogeneous, so it doesn't matter what we
             // use for their ViewHolders.
@@ -64,7 +64,7 @@ class GenreDetailAdapter(private val listener: Listener<Music>) :
 
     override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
         super.onBindViewHolder(holder, position)
-        when (val item = differ.currentList[position]) {
+        when (val item = getItem(position)) {
             is Genre -> (holder as GenreDetailViewHolder).bind(item, listener)
             is Artist -> (holder as ArtistViewHolder).bind(item, listener)
             is Song -> (holder as SongViewHolder).bind(item, listener)
@@ -72,9 +72,11 @@ class GenreDetailAdapter(private val listener: Listener<Music>) :
     }
 
     override fun isItemFullWidth(position: Int): Boolean {
+        if (super.isItemFullWidth(position)) {
+            return true
+        }
         // Genre headers should be full-width in all configurations
-        val item = differ.currentList[position]
+        return getItem(position) is Genre
-        return super.isItemFullWidth(position) || item is Genre
     }
 
     private companion object {

app/src/main/java/org/oxycblt/auxio/home/list/AlbumListFragment.kt

@@ -31,8 +31,8 @@ import org.oxycblt.auxio.home.fastscroll.FastScrollRecyclerView
 import org.oxycblt.auxio.list.*
 import org.oxycblt.auxio.list.ListFragment
 import org.oxycblt.auxio.list.recycler.AlbumViewHolder
+import org.oxycblt.auxio.list.recycler.ListDiffer
 import org.oxycblt.auxio.list.recycler.SelectionIndicatorAdapter
-import org.oxycblt.auxio.list.recycler.SyncListDiffer
 import org.oxycblt.auxio.music.*
 import org.oxycblt.auxio.music.library.Sort
 import org.oxycblt.auxio.playback.formatDurationMs
@@ -67,7 +67,7 @@ class AlbumListFragment :
         }
 
         collectImmediately(homeModel.albumsList, albumAdapter::replaceList)
-        collectImmediately(selectionModel.selected, albumAdapter::setSelectedItems)
+        collectImmediately(selectionModel.selected, ::updateSelection)
         collectImmediately(playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
     }
 
@@ -130,9 +130,13 @@ class AlbumListFragment :
         openMusicMenu(anchor, R.menu.menu_album_actions, item)
     }
 
+    private fun updateSelection(selection: List<Music>) {
+        albumAdapter.setSelected(selection.filterIsInstanceTo(mutableSetOf()))
+    }
+
     private fun updatePlayback(parent: MusicParent?, isPlaying: Boolean) {
         // If an album is playing, highlight it within this adapter.
-        albumAdapter.setPlayingItem(parent as? Album, isPlaying)
+        albumAdapter.setPlaying(parent as? Album, isPlaying)
     }
 
     /**
@@ -140,25 +144,14 @@ class AlbumListFragment :
      * @param listener An [SelectableListListener] to bind interactions to.
      */
     private class AlbumAdapter(private val listener: SelectableListListener<Album>) :
-        SelectionIndicatorAdapter<AlbumViewHolder>() {
+        SelectionIndicatorAdapter<Album, AlbumViewHolder>(
-        private val differ = SyncListDiffer(this, AlbumViewHolder.DIFF_CALLBACK)
+            ListDiffer.Async(AlbumViewHolder.DIFF_CALLBACK)) {
-
-        override val currentList: List<Item>
-            get() = differ.currentList
 
         override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
             AlbumViewHolder.from(parent)
 
         override fun onBindViewHolder(holder: AlbumViewHolder, position: Int) {
-            holder.bind(differ.currentList[position], listener)
+            holder.bind(getItem(position), listener)
-        }
-
-        /**
-         * Asynchronously update the list with new [Album]s.
-         * @param newList The new [Album]s for the adapter to display.
-         */
-        fun replaceList(newList: List<Album>) {
-            differ.replaceList(newList)
         }
     }
 }

app/src/main/java/org/oxycblt/auxio/home/list/ArtistListFragment.kt

@@ -29,9 +29,10 @@ import org.oxycblt.auxio.home.fastscroll.FastScrollRecyclerView
 import org.oxycblt.auxio.list.*
 import org.oxycblt.auxio.list.ListFragment
 import org.oxycblt.auxio.list.recycler.ArtistViewHolder
+import org.oxycblt.auxio.list.recycler.ListDiffer
 import org.oxycblt.auxio.list.recycler.SelectionIndicatorAdapter
-import org.oxycblt.auxio.list.recycler.SyncListDiffer
 import org.oxycblt.auxio.music.Artist
+import org.oxycblt.auxio.music.Music
 import org.oxycblt.auxio.music.MusicMode
 import org.oxycblt.auxio.music.MusicParent
 import org.oxycblt.auxio.music.library.Sort
@@ -48,7 +49,7 @@ class ArtistListFragment :
     FastScrollRecyclerView.PopupProvider,
     FastScrollRecyclerView.Listener {
     private val homeModel: HomeViewModel by activityViewModels()
-    private val homeAdapter = ArtistAdapter(this)
+    private val artistAdapter = ArtistAdapter(this)
 
     override fun onCreateBinding(inflater: LayoutInflater) =
         FragmentHomeListBinding.inflate(inflater)
@@ -58,13 +59,13 @@ class ArtistListFragment :
 
         binding.homeRecycler.apply {
             id = R.id.home_artist_recycler
-            adapter = homeAdapter
+            adapter = artistAdapter
             popupProvider = this@ArtistListFragment
             listener = this@ArtistListFragment
         }
 
-        collectImmediately(homeModel.artistsList, homeAdapter::replaceList)
+        collectImmediately(homeModel.artistsList, artistAdapter::replaceList)
-        collectImmediately(selectionModel.selected, homeAdapter::setSelectedItems)
+        collectImmediately(selectionModel.selected, ::updateSelection)
         collectImmediately(playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
     }
 
@@ -107,9 +108,13 @@ class ArtistListFragment :
         openMusicMenu(anchor, R.menu.menu_artist_actions, item)
     }
 
+    private fun updateSelection(selection: List<Music>) {
+        artistAdapter.setSelected(selection.filterIsInstanceTo(mutableSetOf()))
+    }
+
     private fun updatePlayback(parent: MusicParent?, isPlaying: Boolean) {
         // If an artist is playing, highlight it within this adapter.
-        homeAdapter.setPlayingItem(parent as? Artist, isPlaying)
+        artistAdapter.setPlaying(parent as? Artist, isPlaying)
     }
 
     /**
@@ -117,25 +122,14 @@ class ArtistListFragment :
      * @param listener An [SelectableListListener] to bind interactions to.
      */
     private class ArtistAdapter(private val listener: SelectableListListener<Artist>) :
-        SelectionIndicatorAdapter<ArtistViewHolder>() {
+        SelectionIndicatorAdapter<Artist, ArtistViewHolder>(
-        private val differ = SyncListDiffer(this, ArtistViewHolder.DIFF_CALLBACK)
+            ListDiffer.Async(ArtistViewHolder.DIFF_CALLBACK)) {
-
-        override val currentList: List<Item>
-            get() = differ.currentList
 
         override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
             ArtistViewHolder.from(parent)
 
         override fun onBindViewHolder(holder: ArtistViewHolder, position: Int) {
-            holder.bind(differ.currentList[position], listener)
+            holder.bind(getItem(position), listener)
-        }
-
-        /**
-         * Asynchronously update the list with new [Artist]s.
-         * @param newList The new [Artist]s for the adapter to display.
-         */
-        fun replaceList(newList: List<Artist>) {
-            differ.replaceList(newList)
         }
     }
 }

app/src/main/java/org/oxycblt/auxio/home/list/GenreListFragment.kt

@@ -29,9 +29,10 @@ import org.oxycblt.auxio.home.fastscroll.FastScrollRecyclerView
 import org.oxycblt.auxio.list.*
 import org.oxycblt.auxio.list.ListFragment
 import org.oxycblt.auxio.list.recycler.GenreViewHolder
+import org.oxycblt.auxio.list.recycler.ListDiffer
 import org.oxycblt.auxio.list.recycler.SelectionIndicatorAdapter
-import org.oxycblt.auxio.list.recycler.SyncListDiffer
 import org.oxycblt.auxio.music.Genre
+import org.oxycblt.auxio.music.Music
 import org.oxycblt.auxio.music.MusicMode
 import org.oxycblt.auxio.music.MusicParent
 import org.oxycblt.auxio.music.library.Sort
@@ -47,7 +48,7 @@ class GenreListFragment :
     FastScrollRecyclerView.PopupProvider,
     FastScrollRecyclerView.Listener {
     private val homeModel: HomeViewModel by activityViewModels()
-    private val homeAdapter = GenreAdapter(this)
+    private val genreAdapter = GenreAdapter(this)
 
     override fun onCreateBinding(inflater: LayoutInflater) =
         FragmentHomeListBinding.inflate(inflater)
@@ -57,13 +58,13 @@ class GenreListFragment :
 
         binding.homeRecycler.apply {
             id = R.id.home_genre_recycler
-            adapter = homeAdapter
+            adapter = genreAdapter
             popupProvider = this@GenreListFragment
             listener = this@GenreListFragment
         }
 
-        collectImmediately(homeModel.genresList, homeAdapter::replaceList)
+        collectImmediately(homeModel.genresList, genreAdapter::replaceList)
-        collectImmediately(selectionModel.selected, homeAdapter::setSelectedItems)
+        collectImmediately(selectionModel.selected, ::updateSelection)
         collectImmediately(playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
     }
 
@@ -106,9 +107,13 @@ class GenreListFragment :
         openMusicMenu(anchor, R.menu.menu_artist_actions, item)
     }
 
+    private fun updateSelection(selection: List<Music>) {
+        genreAdapter.setSelected(selection.filterIsInstanceTo(mutableSetOf()))
+    }
+
     private fun updatePlayback(parent: MusicParent?, isPlaying: Boolean) {
         // If a genre is playing, highlight it within this adapter.
-        homeAdapter.setPlayingItem(parent as? Genre, isPlaying)
+        genreAdapter.setPlaying(parent as? Genre, isPlaying)
     }
 
     /**
@@ -116,25 +121,13 @@ class GenreListFragment :
      * @param listener An [SelectableListListener] to bind interactions to.
      */
     private class GenreAdapter(private val listener: SelectableListListener<Genre>) :
-        SelectionIndicatorAdapter<GenreViewHolder>() {
+        SelectionIndicatorAdapter<Genre, GenreViewHolder>(
-        private val differ = SyncListDiffer(this, GenreViewHolder.DIFF_CALLBACK)
+            ListDiffer.Async(GenreViewHolder.DIFF_CALLBACK)) {
-
-        override val currentList: List<Item>
-            get() = differ.currentList
-
         override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
             GenreViewHolder.from(parent)
 
         override fun onBindViewHolder(holder: GenreViewHolder, position: Int) {
-            holder.bind(differ.currentList[position], listener)
+            holder.bind(getItem(position), listener)
-        }
-
-        /**
-         * Asynchronously update the list with new [Genre]s.
-         * @param newList The new [Genre]s for the adapter to display.
-         */
-        fun replaceList(newList: List<Genre>) {
-            differ.replaceList(newList)
         }
     }
 }

app/src/main/java/org/oxycblt/auxio/home/list/SongListFragment.kt

@@ -30,9 +30,10 @@ import org.oxycblt.auxio.home.HomeViewModel
 import org.oxycblt.auxio.home.fastscroll.FastScrollRecyclerView
 import org.oxycblt.auxio.list.*
 import org.oxycblt.auxio.list.ListFragment
+import org.oxycblt.auxio.list.recycler.ListDiffer
 import org.oxycblt.auxio.list.recycler.SelectionIndicatorAdapter
 import org.oxycblt.auxio.list.recycler.SongViewHolder
-import org.oxycblt.auxio.list.recycler.SyncListDiffer
+import org.oxycblt.auxio.music.Music
 import org.oxycblt.auxio.music.MusicMode
 import org.oxycblt.auxio.music.MusicParent
 import org.oxycblt.auxio.music.Song
@@ -50,7 +51,7 @@ class SongListFragment :
     FastScrollRecyclerView.PopupProvider,
     FastScrollRecyclerView.Listener {
     private val homeModel: HomeViewModel by activityViewModels()
-    private val homeAdapter = SongAdapter(this)
+    private val songAdapter = SongAdapter(this)
     // Save memory by re-using the same formatter and string builder when creating popup text
     private val formatterSb = StringBuilder(64)
     private val formatter = Formatter(formatterSb)
@@ -63,13 +64,13 @@ class SongListFragment :
 
         binding.homeRecycler.apply {
             id = R.id.home_song_recycler
-            adapter = homeAdapter
+            adapter = songAdapter
             popupProvider = this@SongListFragment
             listener = this@SongListFragment
         }
 
-        collectImmediately(homeModel.songLists, homeAdapter::replaceList)
+        collectImmediately(homeModel.songLists, songAdapter::replaceList)
-        collectImmediately(selectionModel.selected, homeAdapter::setSelectedItems)
+        collectImmediately(selectionModel.selected, ::updateSelection)
         collectImmediately(
             playbackModel.song, playbackModel.parent, playbackModel.isPlaying, ::updatePlayback)
     }
@@ -136,12 +137,16 @@ class SongListFragment :
         openMusicMenu(anchor, R.menu.menu_song_actions, item)
     }
 
+    private fun updateSelection(selection: List<Music>) {
+        songAdapter.setSelected(selection.filterIsInstanceTo(mutableSetOf()))
+    }
+
     private fun updatePlayback(song: Song?, parent: MusicParent?, isPlaying: Boolean) {
         if (parent == null) {
-            homeAdapter.setPlayingItem(song, isPlaying)
+            songAdapter.setPlaying(song, isPlaying)
         } else {
             // Ignore playback that is not from all songs
-            homeAdapter.setPlayingItem(null, isPlaying)
+            songAdapter.setPlaying(null, isPlaying)
         }
     }
 
@@ -150,25 +155,14 @@ class SongListFragment :
      * @param listener An [SelectableListListener] to bind interactions to.
      */
     private class SongAdapter(private val listener: SelectableListListener<Song>) :
-        SelectionIndicatorAdapter<SongViewHolder>() {
+        SelectionIndicatorAdapter<Song, SongViewHolder>(
-        private val differ = SyncListDiffer(this, SongViewHolder.DIFF_CALLBACK)
+            ListDiffer.Async(SongViewHolder.DIFF_CALLBACK)) {
-
-        override val currentList: List<Item>
-            get() = differ.currentList
 
         override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
             SongViewHolder.from(parent)
 
         override fun onBindViewHolder(holder: SongViewHolder, position: Int) {
-            holder.bind(differ.currentList[position], listener)
+            holder.bind(getItem(position), listener)
-        }
-
-        /**
-         * Asynchronously update the list with new [Song]s.
-         * @param newList The new [Song]s for the adapter to display.
-         */
-        fun replaceList(newList: List<Song>) {
-            differ.replaceList(newList)
         }
     }
 }

app/src/main/java/org/oxycblt/auxio/list/UpdateInstructions.kt

@@ -1,3 +1,20 @@
+/*
+ * Copyright (c) 2023 Auxio Project
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+ 
 package org.oxycblt.auxio.list
 
 /**
@@ -12,8 +29,8 @@ enum class UpdateInstructions {
     DIFF,
 
     /**
-     * Synchronously remove the current list and replace it with a new one. This should be used
+     * Synchronously remove the current list and replace it with a new one. This should be used for
-     * for large diffs with that would cause erratic scroll behavior or in-efficiency.
+     * large diffs with that would cause erratic scroll behavior or in-efficiency.
      */
     REPLACE
-}
+}

app/src/main/java/org/oxycblt/auxio/list/recycler/DiffAdapter.kt

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2023 Auxio Project
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+ 
+package org.oxycblt.auxio.list.recycler
+
+import androidx.recyclerview.widget.RecyclerView
+import org.oxycblt.auxio.list.UpdateInstructions
+
+/**
+ * A [RecyclerView.Adapter] with [ListDiffer] integration.
+ * @param differFactory The [ListDiffer.Factory] that defines the type of [ListDiffer] to use.
+ */
+abstract class DiffAdapter<T, VH : RecyclerView.ViewHolder>(differFactory: ListDiffer.Factory<T>) :
+    RecyclerView.Adapter<VH>() {
+    private val differ = differFactory.new(@Suppress("LeakingThis") this)
+
+    final override fun getItemCount() = differ.currentList.size
+
+    /** The current list of [T] items. */
+    val currentList: List<T>
+        get() = differ.currentList
+
+    /**
+     * Get a [T] item at the given position.
+     * @param at The position to get the item at.
+     * @throws IndexOutOfBoundsException If the index is not in the list bounds/
+     */
+    fun getItem(at: Int) = differ.currentList[at]
+
+    /**
+     * Dynamically determine how to update the list based on the given [UpdateInstructions].
+     * @param newList The new list of [T] items to show.
+     * @param instructions The [UpdateInstructions] specifying how to update the list.
+     */
+    fun submitList(newList: List<T>, instructions: UpdateInstructions) {
+        when (instructions) {
+            UpdateInstructions.DIFF -> diffList(newList)
+            UpdateInstructions.REPLACE -> replaceList(newList)
+        }
+    }
+
+    /**
+     * Update this list using [DiffUtil]. This can simplify the work of updating the list, but can
+     * also cause erratic behavior.
+     * @param newList The new list of [T] items to show.
+     * @param onDone Callback that will be invoked when the update is completed, allowing means to
+     * reset the state.
+     */
+    fun diffList(newList: List<T>, onDone: () -> Unit = {}) = differ.diffList(newList, onDone)
+
+    /**
+     * Visually replace the previous list with a new list. This is useful for large diffs that are
+     * too erratic for [diffList].
+     * @param newList The new list of [T] items to show.
+     */
+    fun replaceList(newList: List<T>) = differ.replaceList(newList)
+}

app/src/main/java/org/oxycblt/auxio/list/recycler/ListDiffer.kt

@@ -0,0 +1,224 @@
+/*
+ * Copyright (c) 2023 Auxio Project
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+ 
+package org.oxycblt.auxio.list.recycler
+
+import androidx.recyclerview.widget.AdapterListUpdateCallback
+import androidx.recyclerview.widget.AsyncDifferConfig
+import androidx.recyclerview.widget.AsyncListDiffer
+import androidx.recyclerview.widget.DiffUtil
+import androidx.recyclerview.widget.ListUpdateCallback
+import androidx.recyclerview.widget.RecyclerView
+import java.lang.reflect.Field
+import org.oxycblt.auxio.util.lazyReflectedField
+import org.oxycblt.auxio.util.requireIs
+
+/**
+ * List differ wrapper that provides more flexibility regarding the way lists are updated.
+ * @author Alexander Capehart (OxygenCobalt)
+ */
+interface ListDiffer<T> {
+    /** The current list of [T] items. */
+    val currentList: List<T>
+
+    /**
+     * Update this list using [DiffUtil]. This can simplify the work of updating the list, but can
+     * also cause erratic behavior.
+     * @param newList The new list of [T] items to show.
+     * @param onDone Callback that will be invoked when the update is completed, allowing means to
+     * reset the state.
+     */
+    fun diffList(newList: List<T>, onDone: () -> Unit = {})
+
+    /**
+     * Visually replace the previous list with a new list. This is useful for large diffs that are
+     * too erratic for [diffList].
+     * @param newList The new list of [T] items to show.
+     */
+    fun replaceList(newList: List<T>)
+
+    /**
+     * Defines the creation of new [ListDiffer] instances. Allows such [ListDiffer]s to be passed as
+     * arguments without reliance on a `this` [RecyclerView.Adapter].
+     */
+    abstract class Factory<T> {
+        /**
+         * Create a new [ListDiffer] bound to the given [RecyclerView.Adapter].
+         * @param adapter The [RecyclerView.Adapter] to bind to.
+         */
+        abstract fun new(adapter: RecyclerView.Adapter<*>): ListDiffer<T>
+    }
+
+    /**
+     * Update lists on another thread. This is useful when large diffs are likely to occur in this
+     * list that would be exceedingly slow with [Blocking].
+     * @param diffCallback A [DiffUtil.ItemCallback] to use for item comparison when diffing the
+     * internal list.
+     */
+    class Async<T>(private val diffCallback: DiffUtil.ItemCallback<T>) : Factory<T>() {
+        override fun new(adapter: RecyclerView.Adapter<*>): ListDiffer<T> =
+            RealAsyncListDiffer(AdapterListUpdateCallback(adapter), diffCallback)
+    }
+
+    /**
+     * Update lists on the main thread. This is useful when many small, discrete list diffs are
+     * likely to occur that would cause [Async] to get race conditions.
+     * @param diffCallback A [DiffUtil.ItemCallback] to use for item comparison when diffing the
+     * internal list.
+     */
+    class Blocking<T>(private val diffCallback: DiffUtil.ItemCallback<T>) : Factory<T>() {
+        override fun new(adapter: RecyclerView.Adapter<*>): ListDiffer<T> =
+            RealBlockingListDiffer(AdapterListUpdateCallback(adapter), diffCallback)
+    }
+}
+
+private class RealAsyncListDiffer<T>(
+    private val updateCallback: ListUpdateCallback,
+    diffCallback: DiffUtil.ItemCallback<T>
+) : ListDiffer<T> {
+    private val inner =
+        AsyncListDiffer(updateCallback, AsyncDifferConfig.Builder(diffCallback).build())
+
+    override val currentList: List<T>
+        get() = inner.currentList
+
+    override fun diffList(newList: List<T>, onDone: () -> Unit) {
+        inner.submitList(newList, onDone)
+    }
+
+    override fun replaceList(newList: List<T>) {
+        if (inner.currentList == newList) {
+            // Nothing to do.
+            return
+        }
+        // Do possibly the most idiotic thing possible and mutate the internal differ state
+        // so we don't have to deal with any disjoint list garbage. This should cancel any prior
+        // updates and correctly set up the list values while still allowing for the same
+        // visual animation as the blocking replaceList.
+        val oldListSize = inner.currentList.size
+        ASD_MAX_GENERATION_FIELD.set(inner, requireIs<Int>(ASD_MAX_GENERATION_FIELD.get(inner)) + 1)
+        ASD_MUTABLE_LIST_FIELD.set(inner, newList.ifEmpty { null })
+        ASD_READ_ONLY_LIST_FIELD.set(inner, newList)
+        updateCallback.onRemoved(0, oldListSize)
+        updateCallback.onInserted(0, newList.size)
+    }
+
+    private companion object {
+        val ASD_MAX_GENERATION_FIELD: Field by
+            lazyReflectedField(AsyncListDiffer::class, "mMaxScheduledGeneration")
+        val ASD_MUTABLE_LIST_FIELD: Field by lazyReflectedField(AsyncListDiffer::class, "mList")
+        val ASD_READ_ONLY_LIST_FIELD: Field by
+            lazyReflectedField(AsyncListDiffer::class, "mReadOnlyList")
+    }
+}
+
+private class RealBlockingListDiffer<T>(
+    private val updateCallback: ListUpdateCallback,
+    private val diffCallback: DiffUtil.ItemCallback<T>
+) : ListDiffer<T> {
+    override var currentList = listOf<T>()
+
+    override fun diffList(newList: List<T>, onDone: () -> Unit) {
+        if (newList === currentList || newList.isEmpty() && currentList.isEmpty()) {
+            onDone()
+            return
+        }
+
+        if (newList.isEmpty()) {
+            val oldListSize = currentList.size
+            currentList = listOf()
+            updateCallback.onRemoved(0, oldListSize)
+            onDone()
+            return
+        }
+
+        if (currentList.isEmpty()) {
+            currentList = newList
+            updateCallback.onInserted(0, newList.size)
+            onDone()
+            return
+        }
+
+        val oldList = currentList
+        val result =
+            DiffUtil.calculateDiff(
+                object : DiffUtil.Callback() {
+                    override fun getOldListSize(): Int {
+                        return oldList.size
+                    }
+
+                    override fun getNewListSize(): Int {
+                        return newList.size
+                    }
+
+                    override fun areItemsTheSame(
+                        oldItemPosition: Int,
+                        newItemPosition: Int
+                    ): Boolean {
+                        val oldItem: T? = oldList[oldItemPosition]
+                        val newItem: T? = newList[newItemPosition]
+                        return if (oldItem != null && newItem != null) {
+                            diffCallback.areItemsTheSame(oldItem, newItem)
+                        } else {
+                            oldItem == null && newItem == null
+                        }
+                    }
+
+                    override fun areContentsTheSame(
+                        oldItemPosition: Int,
+                        newItemPosition: Int
+                    ): Boolean {
+                        val oldItem: T? = oldList[oldItemPosition]
+                        val newItem: T? = newList[newItemPosition]
+                        return if (oldItem != null && newItem != null) {
+                            diffCallback.areContentsTheSame(oldItem, newItem)
+                        } else if (oldItem == null && newItem == null) {
+                            true
+                        } else {
+                            throw AssertionError()
+                        }
+                    }
+
+                    override fun getChangePayload(
+                        oldItemPosition: Int,
+                        newItemPosition: Int
+                    ): Any? {
+                        val oldItem: T? = oldList[oldItemPosition]
+                        val newItem: T? = newList[newItemPosition]
+                        return if (oldItem != null && newItem != null) {
+                            diffCallback.getChangePayload(oldItem, newItem)
+                        } else {
+                            throw AssertionError()
+                        }
+                    }
+                })
+
+        currentList = newList
+        result.dispatchUpdatesTo(updateCallback)
+        onDone()
+    }
+
+    override fun replaceList(newList: List<T>) {
+        if (currentList == newList) {
+            // Nothing to do.
+            return
+        }
+
+        diffList(listOf())
+        diffList(newList)
+    }
+}

app/src/main/java/org/oxycblt/auxio/list/recycler/PlayingIndicatorAdapter.kt

@@ -19,33 +19,27 @@ package org.oxycblt.auxio.list.recycler
 
 import android.view.View
 import androidx.recyclerview.widget.RecyclerView
-import org.oxycblt.auxio.list.Item
-import org.oxycblt.auxio.music.Music
 import org.oxycblt.auxio.util.logD
 
 /**
  * A [RecyclerView.Adapter] that supports indicating the playback status of a particular item.
+ * @param differFactory The [ListDiffer.Factory] that defines the type of [ListDiffer] to use.
  * @author Alexander Capehart (OxygenCobalt)
  */
-abstract class PlayingIndicatorAdapter<VH : RecyclerView.ViewHolder> : RecyclerView.Adapter<VH>() {
+abstract class PlayingIndicatorAdapter<T, VH : RecyclerView.ViewHolder>(
+    differFactory: ListDiffer.Factory<T>
+) : DiffAdapter<T, VH>(differFactory) {
     // There are actually two states for this adapter:
     // - The currently playing item, which is usually marked as "selected" and becomes accented.
     // - Whether playback is ongoing, which corresponds to whether the item's ImageGroup is
     // marked as "playing" or not.
-    private var currentMusic: Music? = null
+    private var currentItem: T? = null
     private var isPlaying = false
 
-    /**
-     * The current list of the adapter. This is used to update items if the indicator state changes.
-     */
-    abstract val currentList: List<Item>
-
-    override fun getItemCount() = currentList.size
-
     override fun onBindViewHolder(holder: VH, position: Int, payloads: List<Any>) {
         // Only try to update the playing indicator if the ViewHolder supports it
         if (holder is ViewHolder) {
-            holder.updatePlayingIndicator(currentList[position] == currentMusic, isPlaying)
+            holder.updatePlayingIndicator(currentList[position] == currentItem, isPlaying)
         }
 
         if (payloads.isEmpty()) {
@@ -56,14 +50,14 @@ abstract class PlayingIndicatorAdapter<VH : RecyclerView.ViewHolder> : RecyclerV
     }
     /**
      * Update the currently playing item in the list.
-     * @param music The [Music] currently being played, or null if it is not being played.
+     * @param item The [T] currently being played, or null if it is not being played.
      * @param isPlaying Whether playback is ongoing or paused.
      */
-    fun setPlayingItem(music: Music?, isPlaying: Boolean) {
+    fun setPlaying(item: T?, isPlaying: Boolean) {
         var updatedItem = false
-        if (currentMusic != music) {
+        if (currentItem != item) {
-            val oldItem = currentMusic
+            val oldItem = currentItem
-            currentMusic = music
+            currentItem = item
 
             // Remove the playing indicator from the old item
             if (oldItem != null) {
@@ -76,8 +70,8 @@ abstract class PlayingIndicatorAdapter<VH : RecyclerView.ViewHolder> : RecyclerV
             }
 
             // Enable the playing indicator on the new item
-            if (music != null) {
+            if (item != null) {
-                val pos = currentList.indexOfFirst { it == music }
+                val pos = currentList.indexOfFirst { it == item }
                 if (pos > -1) {
                     notifyItemChanged(pos, PAYLOAD_PLAYING_INDICATOR_CHANGED)
                 } else {
@@ -94,8 +88,8 @@ abstract class PlayingIndicatorAdapter<VH : RecyclerView.ViewHolder> : RecyclerV
             // We may have already called notifyItemChanged before when checking
             // if the item was being played, so in that case we don't need to
             // update again here.
-            if (!updatedItem && music != null) {
+            if (!updatedItem && item != null) {
-                val pos = currentList.indexOfFirst { it == music }
+                val pos = currentList.indexOfFirst { it == item }
                 if (pos > -1) {
                     notifyItemChanged(pos, PAYLOAD_PLAYING_INDICATOR_CHANGED)
                 } else {

app/src/main/java/org/oxycblt/auxio/list/recycler/SelectionIndicatorAdapter.kt

@@ -24,11 +24,13 @@ import org.oxycblt.auxio.music.Music
 /**
  * A [PlayingIndicatorAdapter] that also supports indicating the selection status of a group of
  * items.
+ * @param differFactory The [ListDiffer.Factory] that defines the type of [ListDiffer] to use.
  * @author Alexander Capehart (OxygenCobalt)
  */
-abstract class SelectionIndicatorAdapter<VH : RecyclerView.ViewHolder> :
+abstract class SelectionIndicatorAdapter<T, VH : RecyclerView.ViewHolder>(
-    PlayingIndicatorAdapter<VH>() {
+    differFactory: ListDiffer.Factory<T>
-    private var selectedItems = setOf<Music>()
+) : PlayingIndicatorAdapter<T, VH>(differFactory) {
+    private var selectedItems = setOf<T>()
 
     override fun onBindViewHolder(holder: VH, position: Int, payloads: List<Any>) {
         super.onBindViewHolder(holder, position, payloads)
@@ -39,9 +41,9 @@ abstract class SelectionIndicatorAdapter<VH : RecyclerView.ViewHolder> :
 
     /**
      * Update the list of selected items.
-     * @param items A list of selected [Music].
+     * @param items A set of selected [T] items.
      */
-    fun setSelectedItems(items: List<Music>) {
+    fun setSelected(items: Set<T>) {
         val oldSelectedItems = selectedItems
         val newSelectedItems = items.toSet()
         if (newSelectedItems == oldSelectedItems) {

app/src/main/java/org/oxycblt/auxio/music/extractor/MetadataExtractor.kt

@@ -64,8 +64,7 @@ class MetadataExtractor(
     /**
      * Returns a flow that parses all [Song.Raw] instances queued by the sub-extractors. This will
      * first delegate to the sub-extractors before parsing the metadata itself.
-     * @param emit A listener that will be invoked with every new [Song.Raw] instance when they are
+     * @return A flow of [Song.Raw] instances.
-     * successfully loaded.
      */
     fun extract() = flow {
         while (true) {
@@ -310,8 +309,9 @@ class Task(context: Context, private val raw: Song.Raw) {
         // Album artist
         comments["musicbrainz_albumartistid"]?.let { raw.albumArtistMusicBrainzIds = it }
         (comments["albumartists"] ?: comments["albumartist"])?.let { raw.albumArtistNames = it }
-        (comments["albumartists_sort"] ?: comments["albumartistsort"])
+        (comments["albumartists_sort"] ?: comments["albumartistsort"])?.let {
-            ?.let { raw.albumArtistSortNames = it }
+            raw.albumArtistSortNames = it
+        }
 
         // Genre
         comments["genre"]?.let { raw.genreNames = it }

app/src/main/java/org/oxycblt/auxio/playback/PlaybackSettings.kt

@@ -199,7 +199,7 @@ interface PlaybackSettings : Settings<PlaybackSettings.Listener> {
             }
         }
 
-        companion object {
+        private companion object {
             const val OLD_KEY_ALT_NOTIF_ACTION = "KEY_ALT_NOTIF_ACTION"
             const val OLD_KEY_LIB_PLAYBACK_MODE = "KEY_SONG_PLAY_MODE2"
             const val OLD_KEY_DETAIL_PLAYBACK_MODE = "auxio_detail_song_play_mode"

app/src/main/java/org/oxycblt/auxio/playback/queue/QueueAdapter.kt

@@ -27,9 +27,10 @@ import com.google.android.material.shape.MaterialShapeDrawable
 import org.oxycblt.auxio.R
 import org.oxycblt.auxio.databinding.ItemQueueSongBinding
 import org.oxycblt.auxio.list.EditableListListener
+import org.oxycblt.auxio.list.recycler.DiffAdapter
+import org.oxycblt.auxio.list.recycler.ListDiffer
 import org.oxycblt.auxio.list.recycler.PlayingIndicatorAdapter
 import org.oxycblt.auxio.list.recycler.SongViewHolder
-import org.oxycblt.auxio.list.recycler.SyncListDiffer
 import org.oxycblt.auxio.music.Song
 import org.oxycblt.auxio.util.*
 
@@ -39,16 +40,13 @@ import org.oxycblt.auxio.util.*
  * @author Alexander Capehart (OxygenCobalt)
  */
 class QueueAdapter(private val listener: EditableListListener<Song>) :
-    RecyclerView.Adapter<QueueSongViewHolder>() {
+    DiffAdapter<Song, QueueSongViewHolder>(ListDiffer.Blocking(QueueSongViewHolder.DIFF_CALLBACK)) {
-    private var differ = SyncListDiffer(this, QueueSongViewHolder.DIFF_CALLBACK)
     // Since PlayingIndicator adapter relies on an item value, we cannot use it for this
     // adapter, as one item can appear at several points in the UI. Use a similar implementation
     // with an index value instead.
     private var currentIndex = 0
     private var isPlaying = false
 
-    override fun getItemCount() = differ.currentList.size
-
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
         QueueSongViewHolder.from(parent)
 
@@ -61,31 +59,13 @@ class QueueAdapter(private val listener: EditableListListener<Song>) :
         payload: List<Any>
     ) {
         if (payload.isEmpty()) {
-            viewHolder.bind(differ.currentList[position], listener)
+            viewHolder.bind(getItem(position), listener)
         }
 
         viewHolder.isFuture = position > currentIndex
         viewHolder.updatePlayingIndicator(position == currentIndex, isPlaying)
     }
 
-    /**
-     * Synchronously update the list with new items. This is exceedingly slow for large diffs, so
-     * only use it for trivial updates.
-     * @param newList The new [Song]s for the adapter to display.
-     */
-    fun submitList(newList: List<Song>) {
-        differ.submitList(newList)
-    }
-
-    /**
-     * Replace the list with a new list. This is exceedingly slow for large diffs, so only use it
-     * for trivial updates.
-     * @param newList The new [Song]s for the adapter to display.
-     */
-    fun replaceList(newList: List<Song>) {
-        differ.replaceList(newList)
-    }
-
     /**
      * Set the position of the currently playing item in the queue. This will mark the item as
      * playing and any previous items as played.

app/src/main/java/org/oxycblt/auxio/playback/queue/QueueFragment.kt

@@ -33,7 +33,6 @@ import org.oxycblt.auxio.playback.PlaybackViewModel
 import org.oxycblt.auxio.ui.ViewBindingFragment
 import org.oxycblt.auxio.util.androidActivityViewModels
 import org.oxycblt.auxio.util.collectImmediately
-import org.oxycblt.auxio.util.logD
 
 /**
  * A [ViewBindingFragment] that displays an editable queue.
@@ -102,13 +101,7 @@ class QueueFragment : ViewBindingFragment<FragmentQueueBinding>(), EditableListL
 
         // Replace or diff the queue depending on the type of change it is.
         val instructions = queueModel.instructions
-        if (instructions?.update == UpdateInstructions.REPLACE) {
+        queueAdapter.submitList(queue, instructions?.update ?: UpdateInstructions.DIFF)
-            logD("Replacing queue")
-            queueAdapter.replaceList(queue)
-        } else {
-            logD("Diffing queue")
-            queueAdapter.submitList(queue)
-        }
         // Update position in list (and thus past/future items)
         queueAdapter.setPosition(index, isPlaying)
 

app/src/main/java/org/oxycblt/auxio/playback/state/PlaybackStateDatabase.kt

@@ -165,7 +165,7 @@ class PlaybackStateDatabase private constructor(context: Context) :
     fun write(state: SavedState?) {
         requireBackgroundThread()
         // Only bother saving a state if a song is actively playing from one.
-        // This is not the case with a null state or a state with an out-of-bounds index.
+        // This is not the case with a null state.
         if (state != null) {
             // Transform saved state into raw state, which can then be written to the database.
             val rawPlaybackState =

app/src/main/java/org/oxycblt/auxio/search/SearchAdapter.kt

@@ -18,7 +18,6 @@
 package org.oxycblt.auxio.search
 
 import android.view.ViewGroup
-import androidx.recyclerview.widget.AsyncListDiffer
 import androidx.recyclerview.widget.RecyclerView
 import org.oxycblt.auxio.list.*
 import org.oxycblt.auxio.list.recycler.*
@@ -30,14 +29,11 @@ import org.oxycblt.auxio.music.*
  * @author Alexander Capehart (OxygenCobalt)
  */
 class SearchAdapter(private val listener: SelectableListListener<Music>) :
-    SelectionIndicatorAdapter<RecyclerView.ViewHolder>(), AuxioRecyclerView.SpanSizeLookup {
+    SelectionIndicatorAdapter<Item, RecyclerView.ViewHolder>(ListDiffer.Async(DIFF_CALLBACK)),
-    private val differ = AsyncListDiffer(this, DIFF_CALLBACK)
+    AuxioRecyclerView.SpanSizeLookup {
-
-    override val currentList: List<Item>
-        get() = differ.currentList
 
     override fun getItemViewType(position: Int) =
-        when (differ.currentList[position]) {
+        when (getItem(position)) {
             is Song -> SongViewHolder.VIEW_TYPE
             is Album -> AlbumViewHolder.VIEW_TYPE
             is Artist -> ArtistViewHolder.VIEW_TYPE
@@ -57,7 +53,7 @@ class SearchAdapter(private val listener: SelectableListListener<Music>) :
         }
 
     override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
-        when (val item = differ.currentList[position]) {
+        when (val item = getItem(position)) {
             is Song -> (holder as SongViewHolder).bind(item, listener)
             is Album -> (holder as AlbumViewHolder).bind(item, listener)
             is Artist -> (holder as ArtistViewHolder).bind(item, listener)
@@ -66,17 +62,7 @@ class SearchAdapter(private val listener: SelectableListListener<Music>) :
         }
     }
 
-    override fun isItemFullWidth(position: Int) = differ.currentList[position] is Header
+    override fun isItemFullWidth(position: Int) = getItem(position) is Header
-
-    /**
-     * Asynchronously update the list with new items. Assumes that the list only contains supported
-     * data..
-     * @param newList The new [Item]s for the adapter to display.
-     * @param callback A block called when the asynchronous update is completed.
-     */
-    fun submitList(newList: List<Item>, callback: () -> Unit) {
-        differ.submitList(newList, callback)
-    }
 
     private companion object {
         /** A comparator that can be used with DiffUtil. */

app/src/main/java/org/oxycblt/auxio/search/SearchFragment.kt

@@ -153,7 +153,7 @@ class SearchFragment : ListFragment<Music, FragmentSearchBinding>() {
         // Don't show the RecyclerView (and it's stray overscroll effects) when there
         // are no results.
         binding.searchRecycler.isInvisible = results.isEmpty()
-        searchAdapter.submitList(results.toMutableList()) {
+        searchAdapter.diffList(results.toMutableList()) {
             // I would make it so that the position is only scrolled back to the top when
             // the query actually changes instead of once every re-creation event, but sadly
             // that doesn't seem possible.
@@ -162,7 +162,7 @@ class SearchFragment : ListFragment<Music, FragmentSearchBinding>() {
     }
 
     private fun updatePlayback(song: Song?, parent: MusicParent?, isPlaying: Boolean) {
-        searchAdapter.setPlayingItem(parent ?: song, isPlaying)
+        searchAdapter.setPlaying(parent ?: song, isPlaying)
     }
 
     private fun handleNavigation(item: Music?) {
@@ -180,7 +180,7 @@ class SearchFragment : ListFragment<Music, FragmentSearchBinding>() {
     }
 
     private fun updateSelection(selected: List<Music>) {
-        searchAdapter.setSelectedItems(selected)
+        searchAdapter.setSelected(selected.toSet())
         if (requireBinding().searchSelectionToolbar.updateSelectionAmount(selected.size) &&
             selected.isNotEmpty()) {
             // Make selection of obscured items easier by hiding the keyboard.

app/src/main/java/org/oxycblt/auxio/settings/AboutFragment.kt

@@ -123,14 +123,15 @@ class AboutFragment : ViewBindingFragment<FragmentAboutBinding>() {
                 if (pkgName == "android") {
                     // No default browser [Must open app chooser, may not be supported]
                     openAppChooser(browserIntent)
-                } else try {
+                } else
-                    browserIntent.setPackage(pkgName)
+                    try {
-                    startActivity(browserIntent)
+                        browserIntent.setPackage(pkgName)
-                } catch (e: ActivityNotFoundException) {
+                        startActivity(browserIntent)
-                    // Not a browser but an app chooser
+                    } catch (e: ActivityNotFoundException) {
-                    browserIntent.setPackage(null)
+                        // Not a browser but an app chooser
-                    openAppChooser(browserIntent)
+                        browserIntent.setPackage(null)
-                }
+                        openAppChooser(browserIntent)
+                    }
             } else {
                 // No app installed to open the link
                 context.showToast(R.string.err_no_app)

app/src/main/java/org/oxycblt/auxio/ui/UISettings.kt

@@ -75,10 +75,8 @@ interface UISettings : Settings<UISettings.Listener> {
                 var accent = sharedPreferences.getInt(OLD_KEY_ACCENT3, 5)
                 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
                     // Accents were previously frozen as soon as the OS was updated to android
-                    // twelve,
+                    // twelve, as dynamic colors were enabled by default. This is no longer the
-                    // as dynamic colors were enabled by default. This is no longer the case, so we
+                    // case, so we need to re-update the setting to dynamic colors here.
-                    // need
-                    // to re-update the setting to dynamic colors here.
                     accent = 16
                 }
 
@@ -96,7 +94,7 @@ interface UISettings : Settings<UISettings.Listener> {
             }
         }
 
-        companion object {
+        private companion object {
             const val OLD_KEY_ACCENT3 = "auxio_accent"
         }
     }

app/src/main/java/org/oxycblt/auxio/util/LangUtil.kt

@@ -39,7 +39,8 @@ fun <T> unlikelyToBeNull(value: T?) =
  * @return A data casted to [T].
  * @throws IllegalStateException If the data cannot be casted to [T].
  */
-inline fun <reified T> requireIs(data: Any): T {
+inline fun <reified T> requireIs(data: Any?): T {
+    requireNotNull(data) { "Unexpected datatype: null" }
     check(data is T) { "Unexpected datatype: ${data::class.simpleName}" }
     return data
 }

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

@@ -8,6 +8,8 @@
     android:background="?attr/colorSurface"
     android:transitionGroup="true">
 
+    <!-- TODO: Try to align the queue bar with the playback bar. -->
+
     <androidx.fragment.app.FragmentContainerView
         android:id="@+id/explore_nav_host"
         android:name="androidx.navigation.fragment.NavHostFragment"