Update playlist class.

lib/state/playlist_state.dart

@@ -0,0 +1,18 @@
+import 'package:state_notifier/state_notifier.dart';
+
+import '../local_storage/key_value_storage.dart';
+import '../type/playlist.dart';
+
+class PlaylistProvider extends StateNotifier<List<Playlist>> {
+  PlaylistProvider() : super([]);
+
+  Future<void> loadPlaylist() async {
+    var storage = KeyValueStorage(playlistsAllKey);
+    var playlistEntities = await storage.getPlaylists();
+    var initState = [...playlistEntities.map(Playlist.fromEntity).toList()];
+    for (var playlist in initState) {
+      await playlist.getPlaylist();
+    }
+    state = initState;
+  }
+}

lib/state/podcast_group.dart

@@ -66,28 +66,22 @@ class PodcastGroup extends Equatable {
   final String color;
 
   /// Id lists of podcasts in group.
-  List<String> _podcastList;
-
-  List<String> get podcastList => _podcastList;
-
-  set podcastList(list) {
-    _podcastList = list;
-  }
+  List<String> podcastList;
 
   PodcastGroup(this.name,
       {this.color = '#000000', String id, List<String> podcastList})
       : id = id ?? Uuid().v4(),
-        _podcastList = podcastList ?? [];
+        podcastList = podcastList ?? [];
 
   Future<void> getPodcasts() async {
     var dbHelper = DBHelper();
-    if (_podcastList != []) {
+    if (podcastList != []) {
       try {
-        _podcasts = await dbHelper.getPodcastLocal(_podcastList);
+        _podcasts = await dbHelper.getPodcastLocal(podcastList);
       } catch (e) {
         await Future.delayed(Duration(milliseconds: 200));
         try {
-          _podcasts = await dbHelper.getPodcastLocal(_podcastList);
+          _podcasts = await dbHelper.getPodcastLocal(podcastList);
         } catch (e) {
           developer.log(e.toString());
         }
@@ -526,13 +520,14 @@ class GroupList extends ChangeNotifier {
     _isLoading = false;
     notifyListeners();
   }
-
+  
+  /// Delete podcsat from device.
   Future<void> removePodcast(
     PodcastLocal podcast,
   ) async {
     _syncRemove(podcast.rssUrl);
-    final id = podcast.id;
-    await _unsubscribe(id);
+    await _unsubscribe(podcast.id);
+    await File(podcast.imagePath)?.delete();
   }
 
   Future<void> saveOrder(PodcastGroup group) async {

lib/type/playlist.dart

@@ -1,16 +1,60 @@
+import 'package:uuid/uuid.dart';
+
 import '../local_storage/key_value_storage.dart';
 import '../local_storage/sqflite_localpodcast.dart';
 import 'episodebrief.dart';
 
+class PlaylistEntity {
+  final String name;
+  final String id;
+  final List<String> episodeList;
+
+  PlaylistEntity(this.name, this.id, this.episodeList);
+
+  Map<String, Object> toJson() {
+    return {'name': name, 'id': id, 'episodeList': episodeList};
+  }
+
+  static PlaylistEntity fromJson(Map<String, Object> json) {
+    var list = List<String>.from(json['episodeList']);
+    return PlaylistEntity(json['name'] as String, json['id'] as String, list);
+  }
+}
+
 class Playlist {
-  String name;
+  /// Playlist name. the default playlist is named "Playlist".
+  final String name;
+
+  /// Unique id for playlist.
+  final String id;
+
+  /// Episode url list for playlist.
+  final List<String> episodeList;
+
+  Playlist(this.name, {String id, List<String> episodeList})
+      : id = id ?? Uuid().v4(),
+        episodeList = episodeList ?? [];
+
+  PlaylistEntity toEntity() {
+    return PlaylistEntity(name, id, episodeList);
+  }
+
+  static Playlist fromEntity(PlaylistEntity entity) {
+    return Playlist(
+      entity.name,
+      id: entity.id,
+      episodeList: entity.episodeList,
+    );
+  }
+
   final DBHelper _dbHelper = DBHelper();
-  List<EpisodeBrief> _playlist;
+  List<EpisodeBrief> _playlist = [];
   List<EpisodeBrief> get playlist => _playlist;
   final KeyValueStorage _playlistStorage = KeyValueStorage(playlistKey);
 
   Future<void> getPlaylist() async {
     var urls = await _playlistStorage.getStringList();
+    episodeList.addAll(urls);
     if (urls.length == 0) {
       _playlist = [];
     } else {