enable drag and drop reordering

ui/widgets/tracklist.go

@@ -33,6 +33,9 @@ type TracklistOptions struct {
 	// or to use the number from the track's metadata
 	AutoNumber bool
 
+	// Reorderable sets whether the tracklist supports drag-and-drop reordering.
+	Reorderable bool
+
 	// ShowDiscNumber sets whether to display the disc number as part of the '#' column,
 	// (with format %d.%02d). Only applies if AutoNumber==false.
 	ShowDiscNumber bool
@@ -74,6 +77,7 @@ type Tracklist struct {
 	OnDownload          func(tracks []*mediaprovider.Track, downloadName string)
 	OnShare             func(trackID string)
 	OnPlaySongRadio     func(track *mediaprovider.Track)
+	OnReorderTracks     func(trackIDs []string, insertPos int)
 
 	OnShowArtistPage func(artistID string)
 	OnShowAlbumPage  func(albumID string)
@@ -182,6 +186,17 @@ func NewTracklist(tracks []*mediaprovider.Track, im *backend.ImageManager, useCo
 				t.OnTrackShown(itemID)
 			}
 		})
+	t.list.OnDragBegin = func(id int) {
+		if !t.tracks[id].Selected {
+			t.selectTrack(id)
+			t.list.Refresh()
+		}
+	}
+	t.list.OnDragEnd = func(dragged, insertPos int) {
+		if t.OnReorderTracks != nil {
+			t.OnReorderTracks(t.SelectedTrackIDs(), insertPos)
+		}
+	}
 	t.container = container.NewBorder(t.hdr, nil, nil, nil, t.list)
 	return t
 }
@@ -371,6 +386,7 @@ func (t *Tracklist) CreateRenderer() fyne.WidgetRenderer {
 }
 
 func (t *Tracklist) Refresh() {
+	t.list.EnableDragging = t.Options.Reorderable
 	t.hdr.DisableSorting = t.Options.DisableSorting
 	t.BaseWidget.Refresh()
 }