Removed "PlaylistSongs" field, in order to maintain one source of truth (Playlist.Songs). No not allow reordering when a filter is present on the playlist.

Harmonia.WinUI/ViewModels/PlaylistDetailViewModel.cs

@@ -56,19 +56,6 @@ public partial class PlaylistDetailViewModel : ViewModelBase
         }
     }
 
-    private ObservableCollection<PlaylistSong> _playlistSongs = [];
-    public ObservableCollection<PlaylistSong> PlaylistSongs
-    {
-        get
-        {
-            return _playlistSongs;
-        }
-        set
-        {
-            SetProperty(ref _playlistSongs, value);
-        }
-    }
-
     private string? _filter;
     public string? Filter
     {
@@ -79,10 +66,13 @@ public partial class PlaylistDetailViewModel : ViewModelBase
         set
         {
             SetProperty(ref _filter, value);
+            OnPropertyChanged(nameof(CanReorderSongs));
             RestartFilterTimer();
         }
     }
 
+    public bool CanReorderSongs => string.IsNullOrWhiteSpace(Filter);
+
     private ObservableCollection<PlaylistSong> _filteredPlaylistSongs = [];
     public ObservableCollection<PlaylistSong> FilteredPlaylistSongs
     {
@@ -123,6 +113,8 @@ public partial class PlaylistDetailViewModel : ViewModelBase
 
     public bool IsUserUpdating { get; set; }
     private bool _isUserInitiatingSongChange;
+    private PlaylistSong? _pendingMovedSong;
+    private int _pendingMovedSongIndex = -1;
 
     public event EventHandler? PlayingSongChangedAutomatically;
 
@@ -152,10 +144,7 @@ public partial class PlaylistDetailViewModel : ViewModelBase
         FilteredPlaylistSongs.CollectionChanged += OnFilteredPlaylistSongsCollectionChanged;
 
         Playlist = _playlistManager.CurrentPlaylist; // Testing
-        UpdatePlaylistSongs(Playlist);
+        UpdateFilteredSongs();
-
-        // Testing
-        //Task.Run(() => PlayDemoSong(playlistRepository));
     }
 
     private void OnFilteredPlaylistSongsCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
@@ -163,47 +152,42 @@ public partial class PlaylistDetailViewModel : ViewModelBase
         if (IsUserUpdating == false)
             return;
 
-        int x = 1;
+        // A drag-reorder in the ListView raises a Remove followed by an Add for the same item.
+        // Reordering is only enabled while unfiltered, so view indices map 1:1 to Playlist.Songs.
+        switch (e.Action)
+        {
+            case NotifyCollectionChangedAction.Remove:
+                _pendingMovedSong = e.OldItems?.Cast<PlaylistSong>().FirstOrDefault();
+                _pendingMovedSongIndex = e.OldStartingIndex;
+                break;
+            case NotifyCollectionChangedAction.Add:
+                PlaylistSong? addedSong = e.NewItems?.Cast<PlaylistSong>().FirstOrDefault();
+
+                if (addedSong != null && addedSong == _pendingMovedSong)
+                {
+                    MoveSongInPlaylist(_pendingMovedSongIndex, e.NewStartingIndex);
+                }
+
+                _pendingMovedSong = null;
+                _pendingMovedSongIndex = -1;
+                break;
+        }
     }
 
-    //private async Task PlayDemoSong(IPlaylistRepository playlistRepository)
+    private void MoveSongInPlaylist(int oldIndex, int newIndex)
-    //{
-    //    if (playlistRepository.Get().Count == 0)
-    //    {
-    //        playlistRepository.AddPlaylist();
-    //    }
-
-    //    Playlist playlist = playlistRepository.Get().First();
-
-    //    if (playlist.Songs.Count > 0)
-    //        await _audioPlayer.LoadAsync(playlist.Songs[0], PlaybackMode.LoadOnly);
-    //}
-
-    private void UpdatePlaylistSongs(Playlist? playlist)
     {
-        PlaylistSong[] playlistSongs = playlist?.Songs.ToArray() ?? [];
+        if (Playlist == null || oldIndex < 0 || oldIndex == newIndex)
+            return;
 
-        PlaylistSongs = [.. playlistSongs];
+        Playlist.MoveSong(oldIndex, newIndex);
-        UpdateFilteredSongs();
     }
 
     private void OnPlaylistChanged(object? sender, EventArgs e)
     {
-        if (Playlist != null)
+        Playlist?.PlaylistUpdated -= OnPlaylistUpdated;
-        {
-            Playlist.PlaylistUpdated -= OnPlaylistUpdated;
-        }
-
         Playlist = _audioPlayer.Playlist;
+        Playlist?.PlaylistUpdated += OnPlaylistUpdated;
 
-        if (Playlist != null)
-        {
-            Playlist.PlaylistUpdated += OnPlaylistUpdated;
-        }
-
-        PlaylistSong[] playlistSongs = _audioPlayer.Playlist?.Songs.ToArray() ?? [];
-
-        PlaylistSongs = [.. playlistSongs];
         UpdateFilteredSongs();
     }
 
@@ -215,32 +199,23 @@ public partial class PlaylistDetailViewModel : ViewModelBase
         switch (e.Action)
         {
             case PlaylistUpdateAction.Add:
-                _dispatcherQueue.TryEnqueue(() => AddSongs(e.Songs, e.Index));
-                break;
             case PlaylistUpdateAction.Remove:
-                _dispatcherQueue.TryEnqueue(() => RemoveSongsFromCollection(e.Songs));
+                _dispatcherQueue.TryEnqueue(UpdateFilteredSongs);
+                break;
+            case PlaylistUpdateAction.Move:
+            case PlaylistUpdateAction.Reset:
+                _dispatcherQueue.TryEnqueue(() => ApplyReorderedSongs(e.Songs));
                 break;
         }
     }
 
-    private void AddSongs(PlaylistSong[] playlistSongs, int index = 0)
+    private void ApplyReorderedSongs(PlaylistSong[] playlistSongs)
     {
-        // TODO: Performance improvements
+        // UpdateFilteredSongs assumes the projection order matches Playlist.Songs order,
-        int currentIndex = index;
+        // so remove reordered songs first to let them be reinserted at their new positions.
-
         foreach (PlaylistSong playlistSong in playlistSongs)
         {
-            PlaylistSongs.Insert(currentIndex++, playlistSong);
+            FilteredPlaylistSongs.Remove(playlistSong);
-        }
-
-        UpdateFilteredSongs();
-    }
-
-    private void RemoveSongsFromCollection(PlaylistSong[] playlistSongs)
-    {
-        foreach (PlaylistSong playlistSong in playlistSongs)
-        {
-            PlaylistSongs.Remove(playlistSong);
         }
 
         UpdateFilteredSongs();

Harmonia.WinUI/Views/PlaylistDetailView.xaml

@@ -184,11 +184,11 @@
             Name="PlaylistListView"
             ItemsSource="{Binding FilteredPlaylistSongs}"
             ItemTemplate="{StaticResource SongTemplate}"
-            CanReorderItems="True"
+            CanReorderItems="{Binding CanReorderSongs, Mode=OneWay}"
-            CanDragItems="True"
+            CanDragItems="{Binding CanReorderSongs, Mode=OneWay}"
             DragItemsStarting="PlaylistListView_DragItemsStarting"
             DragItemsCompleted="PlaylistListView_DragItemsCompleted"
-            AllowDrop="True"
+            AllowDrop="{Binding CanReorderSongs, Mode=OneWay}"
             SelectionMode="Extended"
             SelectionChanged="PlaylistListView_SelectionChanged">
             <ListView.ContextFlyout>