Use PageStorage to store state

lib/components/appbar.dart

@@ -281,7 +281,9 @@ class _FilledTabBarState extends State<FilledTabBar> {
 
   _IndicatorPainter? painter;
 
-  var scrollController = ScrollController();
+  var scrollController = ScrollController(
+    keepScrollOffset: false
+  );
 
   var tabBarKey = GlobalKey();
 
@@ -298,12 +300,20 @@ class _FilledTabBarState extends State<FilledTabBar> {
     super.dispose();
   }
 
+  PageStorageBucket get bucket => PageStorage.of(context);
+
   @override
   void didChangeDependencies() {
     _controller = widget.controller ?? DefaultTabController.of(context);
     _controller.animation!.addListener(onTabChanged);
     initPainter();
     super.didChangeDependencies();
+    var prevIndex = bucket.readState(context) as int?;
+    if (prevIndex != null && prevIndex != _controller.index) {
+      Future.microtask(() {
+        _controller.index = prevIndex;
+      });
+    }
   }
 
   @override
@@ -387,6 +397,7 @@ class _FilledTabBarState extends State<FilledTabBar> {
     }
     updateScrollOffset(i);
     previousIndex = i;
+    bucket.writeState(context, i);
   }
 
   void updateScrollOffset(int i) {

lib/components/comic.dart

@@ -865,6 +865,39 @@ class ComicListState extends State<ComicList> {
 
   String? _nextUrl;
 
+  Map<String, dynamic> get state => {
+    'maxPage': _maxPage,
+    'data': _data,
+    'page': _page,
+    'error': _error,
+    'loading': _loading,
+    'nextUrl': _nextUrl,
+  };
+
+  void restoreState(Map<String, dynamic>? state) {
+    if (state == null) {
+      return;
+    }
+    _maxPage = state['maxPage'];
+    _data.clear();
+    _data.addAll(state['data']);
+    _page = state['page'];
+    _error = state['error'];
+    _loading.clear();
+    _loading.addAll(state['loading']);
+    _nextUrl = state['nextUrl'];
+  }
+
+  void storeState() {
+    PageStorage.of(context).writeState(context, state);
+  }
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    restoreState(PageStorage.of(context).readState(context));
+  }
+
   void remove(Comic c) {
     if (_data[_page] == null || !_data[_page]!.remove(c)) {
       for (var page in _data.values) {
@@ -1025,6 +1058,7 @@ class ComicListState extends State<ComicList> {
       }
     } finally {
       _loading[page] = false;
+      storeState();
     }
   }
 
@@ -1073,6 +1107,7 @@ class ComicListState extends State<ComicList> {
       );
     }
     return SmoothCustomScrollView(
+      key: const PageStorageKey('scroll'),
       controller: widget.controller,
       slivers: [
         if (widget.leadingSliver != null) widget.leadingSliver!,

lib/pages/categories_page.dart

@@ -53,6 +53,7 @@ class CategoriesPage extends StatelessWidget {
             child: Column(
               children: [
                 FilledTabBar(
+                  key: PageStorageKey(categories.toString()),
                   tabs: categories.map((e) {
                     String title = e;
                     try {

lib/pages/explore_page.dart

@@ -110,7 +110,7 @@ class _ExplorePageState extends State<ExplorePage>
     return Tab(text: i.ts(comicSource.key), key: Key(i));
   }
 
-  Widget buildBody(String i) => _SingleExplorePage(i, key: Key(i));
+  Widget buildBody(String i) => _SingleExplorePage(i, key: PageStorageKey(i));
 
   Widget buildEmpty() {
     var msg = "No Explore Pages".tl;
@@ -147,7 +147,7 @@ class _ExplorePageState extends State<ExplorePage>
 
     Widget tabBar = Material(
       child: FilledTabBar(
-        key: Key(pages.toString()),
+        key: PageStorageKey(pages.toString()),
         tabs: pages.map((e) => buildTab(e)).toList(),
         controller: controller,
       ),
@@ -240,12 +240,6 @@ class _SingleExplorePageState extends StateWithController<_SingleExplorePage>
     with AutomaticKeepAliveClientMixin<_SingleExplorePage> {
   late final ExplorePageData data;
 
-  bool loading = true;
-
-  String? message;
-
-  List<ExplorePagePart>? parts;
-
   late final String comicSourceKey;
 
   int key = 0;
@@ -288,9 +282,19 @@ class _SingleExplorePageState extends StateWithController<_SingleExplorePage>
   Widget build(BuildContext context) {
     super.build(context);
     if (data.loadMultiPart != null) {
-      return buildMultiPart();
+      return _MultiPartExplorePage(
+        key: PageStorageKey(key),
+        data: data,
+        controller: scrollController,
+        comicSourceKey: comicSourceKey,
+      );
     } else if (data.loadPage != null || data.loadNext != null) {
-      return buildComicList();
+      return ComicList(
+        loadPage: data.loadPage,
+        loadNext: data.loadNext,
+        key: PageStorageKey(key),
+        controller: scrollController,
+      );
     } else if (data.loadMixed != null) {
       return _MixedExplorePage(
         data,
@@ -305,74 +309,14 @@ class _SingleExplorePageState extends StateWithController<_SingleExplorePage>
     }
   }
 
-  Widget buildComicList() {
-    return ComicList(
-      loadPage: data.loadPage,
-      loadNext: data.loadNext,
-      key: ValueKey(key),
-      controller: scrollController,
-    );
-  }
-
-  void load() async {
-    var res = await data.loadMultiPart!();
-    loading = false;
-    if (mounted) {
-      setState(() {
-        if (res.error) {
-          message = res.errorMessage;
-        } else {
-          parts = res.data;
-        }
-      });
-    }
-  }
-
-  Widget buildMultiPart() {
-    if (loading) {
-      load();
-      return const Center(
-        child: CircularProgressIndicator(),
-      );
-    } else if (message != null) {
-      return NetworkError(
-        message: message!,
-        retry: refresh,
-        withAppbar: false,
-      );
-    } else {
-      return buildPage();
-    }
-  }
-
-  Widget buildPage() {
-    return SmoothCustomScrollView(
-      controller: scrollController,
-      slivers: _buildPage().toList(),
-    );
-  }
-
-  Iterable<Widget> _buildPage() sync* {
-    for (var part in parts!) {
-      yield* _buildExplorePagePart(part, comicSourceKey);
-    }
-  }
-
   @override
   Object? get tag => widget.title;
 
   @override
   void refresh() {
-    message = null;
-    if (data.loadMultiPart != null) {
-      setState(() {
-        loading = true;
-      });
-    } else {
-      setState(() {
-        key++;
-      });
-    }
+    setState(() {
+      key++;
+    });
   }
 
   @override
@@ -393,7 +337,8 @@ class _SingleExplorePageState extends StateWithController<_SingleExplorePage>
 }
 
 class _MixedExplorePage extends StatefulWidget {
-  const _MixedExplorePage(this.data, this.sourceKey, {super.key, this.controller});
+  const _MixedExplorePage(this.data, this.sourceKey,
+      {super.key, this.controller});
 
   final ExplorePageData data;
 
@@ -518,3 +463,112 @@ Iterable<Widget> _buildExplorePagePart(
   yield buildTitle(part);
   yield buildComics(part);
 }
+
+class _MultiPartExplorePage extends StatefulWidget {
+  const _MultiPartExplorePage({
+    super.key,
+    required this.data,
+    required this.controller,
+    required this.comicSourceKey,
+  });
+
+  final ExplorePageData data;
+
+  final ScrollController controller;
+
+  final String comicSourceKey;
+
+  @override
+  State<_MultiPartExplorePage> createState() => _MultiPartExplorePageState();
+}
+
+class _MultiPartExplorePageState extends State<_MultiPartExplorePage> {
+  late final ExplorePageData data;
+
+  List<ExplorePagePart>? parts;
+
+  bool loading = true;
+
+  String? message;
+
+  Map<String, dynamic> get state => {
+    "loading": loading,
+    "message": message,
+    "parts": parts,
+  };
+
+  void restoreState(dynamic state) {
+    if (state == null) return;
+    loading = state["loading"];
+    message = state["message"];
+    parts = state["parts"];
+  }
+
+  void storeState() {
+    PageStorage.of(context).writeState(context, state);
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    data = widget.data;
+  }
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    restoreState(PageStorage.of(context).readState(context));
+  }
+
+  void load() async {
+    var res = await data.loadMultiPart!();
+    loading = false;
+    if (mounted) {
+      setState(() {
+        if (res.error) {
+          message = res.errorMessage;
+        } else {
+          parts = res.data;
+        }
+      });
+      storeState();
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (loading) {
+      load();
+      return const Center(
+        child: CircularProgressIndicator(),
+      );
+    } else if (message != null) {
+      return NetworkError(
+        message: message!,
+        retry: () {
+          setState(() {
+            loading = true;
+            message = null;
+          });
+        },
+        withAppbar: false,
+      );
+    } else {
+      return buildPage();
+    }
+  }
+
+  Widget buildPage() {
+    return SmoothCustomScrollView(
+      key: const PageStorageKey('scroll'),
+      controller: widget.controller,
+      slivers: _buildPage().toList(),
+    );
+  }
+
+  Iterable<Widget> _buildPage() sync* {
+    for (var part in parts!) {
+      yield* _buildExplorePagePart(part, widget.comicSourceKey);
+    }
+  }
+}

lib/pages/main_page.dart

@@ -62,10 +62,18 @@ class _MainPageState extends State<MainPage> {
   }
 
   final _pages = [
-    const HomePage(),
-    const FavoritesPage(),
-    const ExplorePage(),
-    const CategoriesPage(),
+    const HomePage(
+      key: PageStorageKey('home'),
+    ),
+    const FavoritesPage(
+      key: PageStorageKey('favorites'),
+    ),
+    const ExplorePage(
+      key: PageStorageKey('explore'),
+    ),
+    const CategoriesPage(
+      key: PageStorageKey('categories'),
+    ),
   ];
 
   var index = 0;