feat(flutter): 首页频道行滚动吸顶

lib/pages/home/home_browse_view.dart

@@ -25,7 +25,6 @@ const double _channelGap = 20;
 const double _channelUnderlineWidth = 18;
 const double _channelUnderlineHeight = 2;
 const double _channelUnderlineGap = 4;
-const double _channelOverlayTop = 8;
 const double _channelFontSize = 15;
 const List<Shadow> _channelTextShadows = [
   Shadow(color: Colors.black54, blurRadius: 5, offset: Offset(0, 1)),
@@ -58,11 +57,14 @@ class HomeBrowseView extends StatefulWidget {
 
 class _HomeBrowseViewState extends State<HomeBrowseView> {
   late final HomeBrowseLogic logic;
+  final ScrollController _scroll = ScrollController();
+  bool _channelsPinned = false;
 
   @override
   void initState() {
     super.initState();
     logic = HomeBrowseLogic(history: context.read<WatchHistoryRepository>());
+    _scroll.addListener(_onScroll);
   }
 
   @override
@@ -73,10 +75,33 @@ class _HomeBrowseViewState extends State<HomeBrowseView> {
 
   @override
   void dispose() {
+    _scroll.removeListener(_onScroll);
+    _scroll.dispose();
     logic.dispose();
     super.dispose();
   }
 
+  /// 滚过 hero 后频道行切成吸顶态，未过阈值时仍叠在轮播图上。
+  void _onScroll() {
+    if (!_scroll.hasClients) return;
+    final pinned =
+        _scroll.offset >= AppDimens.heroBannerHeight - _channelRowHeight;
+    if (pinned != _channelsPinned) {
+      setState(() => _channelsPinned = pinned);
+    }
+  }
+
+  /// 频道行只横向滚动，纵向拖动转交给页面列表，避免挡住上滑。
+  void _scrollPageBy(DragUpdateDetails details) {
+    if (!_scroll.hasClients) return;
+    final position = _scroll.position;
+    _scroll.jumpTo(
+      (_scroll.offset - details.delta.dy)
+          .clamp(position.minScrollExtent, position.maxScrollExtent)
+          .toDouble(),
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
     return ListenableBuilder(
@@ -103,19 +128,63 @@ class _HomeBrowseViewState extends State<HomeBrowseView> {
   }
 
   Widget _body(AppLocalizations l10n, CatalogController catalog) {
-    return RefreshIndicator(
-      key: const Key('home-refresh'),
-      color: AppColors.blue,
-      backgroundColor: AppColors.card,
-      onRefresh: () async {
-        await Future.wait([catalog.load(), logic.refreshRecent()]);
-      },
-      child: ListView(
-        key: const Key('home-browse-page'),
-        physics: const AlwaysScrollableScrollPhysics(),
-        padding: const EdgeInsets.only(bottom: AppDimens.spaceXl),
-        children: _sections(l10n, catalog),
+    final source = catalog.dramas;
+    final banners = catalog.banners.isEmpty
+        ? _fallbackBanners(source)
+        : catalog.banners;
+    final hasBanner = banners.isNotEmpty;
+    final pinned = !hasBanner || _channelsPinned;
+    return Stack(
+      children: [
+        Positioned.fill(
+          child: RefreshIndicator(
+            key: const Key('home-refresh'),
+            color: AppColors.blue,
+            backgroundColor: AppColors.card,
+            onRefresh: () async {
+              await Future.wait([catalog.load(), logic.refreshRecent()]);
+            },
+            child: ListView(
+              key: const Key('home-browse-page'),
+              controller: _scroll,
+              physics: const AlwaysScrollableScrollPhysics(),
+              padding: const EdgeInsets.only(bottom: AppDimens.spaceXl),
+              children: _sections(l10n, catalog),
+            ),
+          ),
+        ),
+        Positioned(
+          top: 0,
+          left: 0,
+          right: 0,
+          child: _channelBar(
+            l10n,
+            pinned: pinned,
+            overImage: hasBanner && !pinned,
+          ),
+        ),
+      ],
+    );
+  }
+
+  Widget _channelBar(
+    AppLocalizations l10n, {
+    required bool pinned,
+    required bool overImage,
+  }) {
+    final content = GestureDetector(
+      behavior: HitTestBehavior.opaque,
+      onVerticalDragUpdate: _scrollPageBy,
+      child: _channels(l10n, overImage: overImage),
+    );
+    if (!pinned) return content;
+    return DecoratedBox(
+      key: const Key('home-channels-pinned'),
+      decoration: const BoxDecoration(
+        color: AppColors.ink,
+        border: Border(bottom: BorderSide(color: AppColors.border)),
       ),
+      child: content,
     );
   }
 
@@ -127,10 +196,7 @@ class _HomeBrowseViewState extends State<HomeBrowseView> {
         ? _fallbackBanners(source)
         : catalog.banners;
     return [
-      if (banners.isNotEmpty)
-        _heroWithChannels(l10n, banners, source)
-      else
-        _channels(l10n),
+      if (banners.isNotEmpty) _hero(banners, source),
       if (continueItem != null) ...[
         _continueHeader(l10n),
         ContinueWatchingCard(
@@ -195,29 +261,6 @@ class _HomeBrowseViewState extends State<HomeBrowseView> {
     ),
   );
 
-  /// 频道行叠加在 hero 轮播之上；无 banner 时作为普通行显示。
-  Widget _heroWithChannels(
-    AppLocalizations l10n,
-    List<FeedBanner> banners,
-    List<Drama> dramas,
-  ) {
-    return SizedBox(
-      key: const Key('home-hero-section'),
-      height: AppDimens.heroBannerHeight,
-      child: Stack(
-        children: [
-          Positioned.fill(child: _hero(banners, dramas)),
-          Positioned(
-            top: _channelOverlayTop,
-            left: 0,
-            right: 0,
-            child: _channels(l10n, overImage: true),
-          ),
-        ],
-      ),
-    );
-  }
-
   Widget _channels(AppLocalizations l10n, {bool overImage = false}) {
     final entries = [
       (HomeChannel.hot, l10n.hot),