播放列表持久化设计、播放列表点击显示当前播放歌曲的列表内位置

lib/pages/playlist_page.dart

@@ -1,11 +1,175 @@
+// lib/pages/playlist_page.dart
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import '../services/audio_service.dart';
-import '../constants/ui_constants.dart';
 
-class PlaylistPage extends StatelessWidget {
+class PlaylistPage extends StatefulWidget {
   const PlaylistPage({super.key});
 
+  @override
+  State<PlaylistPage> createState() => _PlaylistPageState();
+}
+
+class _PlaylistPageState extends State<PlaylistPage> {
+  final ScrollController _scrollController = ScrollController();
+  final GlobalKey _currentTagKey = GlobalKey();
+
+  bool _hasScrolledToCurrent = false;
+  int _retryCount = 0;
+  static const int _maxRetries = 3;
+
+  // ⭐ 统一滚动时长 1.5 秒
+  static const Duration _scrollDuration = Duration(milliseconds: 1500);
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      _scrollToCurrentSong();
+    });
+  }
+
+  @override
+  void dispose() {
+    _scrollController.dispose();
+    super.dispose();
+  }
+
+  double _calculateAverageItemHeight(int itemCount) {
+    final maxExtent = _scrollController.position.maxScrollExtent;
+    if (maxExtent <= 0 || itemCount <= 0) return 72.0;
+    return maxExtent / itemCount;
+  }
+
+  double _calculateTargetOffset(
+      int currentIndex, int totalCount, double avgHeight) {
+    final viewportHeight = _scrollController.position.viewportDimension;
+    return (currentIndex * avgHeight) - (viewportHeight / 2) + (avgHeight / 2);
+  }
+
+  Future<void> _scrollToCurrentSong() async {
+    if (_hasScrolledToCurrent) return;
+
+    final service = context.read<AudioService>();
+    final queue = service.queue;
+    final currentIndex = service.currentIndex;
+
+    if (queue.isEmpty || currentIndex < 0 || currentIndex >= queue.length) {
+      return;
+    }
+
+    await Future.delayed(const Duration(milliseconds: 300));
+    if (!mounted) return;
+
+    final totalCount = queue.length;
+    final avgHeight = _calculateAverageItemHeight(totalCount);
+    final maxExtent = _scrollController.position.maxScrollExtent;
+
+    var tagContext = _currentTagKey.currentContext;
+    if (tagContext != null) {
+      await _calibrateWithTag(tagContext);
+      _hasScrolledToCurrent = true;
+      return;
+    }
+
+    // ⭐ 粗定位：1.5 秒平滑滚动
+    final targetOffset =
+        _calculateTargetOffset(currentIndex, totalCount, avgHeight);
+    final clampedOffset = targetOffset.clamp(0.0, maxExtent);
+
+    await _scrollController.animateTo(
+      clampedOffset,
+      duration: _scrollDuration,
+      curve: Curves.easeOutCubic,
+    );
+    if (!mounted) return;
+
+    await WidgetsBinding.instance.endOfFrame;
+    if (!mounted) return;
+
+    tagContext = _currentTagKey.currentContext;
+    if (tagContext != null) {
+      await _calibrateWithTag(tagContext);
+      _hasScrolledToCurrent = true;
+      return;
+    }
+
+    // ⭐ 迭代修正：每次 1.5 秒平滑滚动
+    _retryCount = 0;
+    var currentOffset = _scrollController.offset;
+    var lastOffset = currentOffset;
+
+    while (_retryCount < _maxRetries) {
+      _retryCount++;
+
+      final viewportHeight = _scrollController.position.viewportDimension;
+      final step = viewportHeight * 0.5;
+      final direction = (currentIndex > totalCount / 2) ? -1 : 1;
+      final newOffset =
+          (currentOffset + direction * step).clamp(0.0, maxExtent);
+
+      if ((newOffset - currentOffset).abs() < 50) {
+        final bigStep = viewportHeight * 0.8 * direction;
+        final forcedOffset = (currentOffset + bigStep).clamp(0.0, maxExtent);
+        await _scrollController.animateTo(
+          forcedOffset,
+          duration: _scrollDuration,
+          curve: Curves.easeOutCubic,
+        );
+      } else {
+        await _scrollController.animateTo(
+          newOffset,
+          duration: _scrollDuration,
+          curve: Curves.easeOutCubic,
+        );
+      }
+
+      if (!mounted) return;
+
+      await WidgetsBinding.instance.endOfFrame;
+      if (!mounted) return;
+
+      tagContext = _currentTagKey.currentContext;
+      if (tagContext != null) {
+        await _calibrateWithTag(tagContext);
+        _hasScrolledToCurrent = true;
+        return;
+      }
+
+      currentOffset = _scrollController.offset;
+      if ((currentOffset - lastOffset).abs() < 10) break;
+      lastOffset = currentOffset;
+    }
+
+    _hasScrolledToCurrent = true;
+  }
+
+  /// 精确定位：1.5 秒平滑滚动
+  Future<void> _calibrateWithTag(BuildContext tagContext) async {
+    final renderBox = tagContext.findRenderObject() as RenderBox?;
+    if (renderBox == null) return;
+
+    final tagPosition = renderBox.localToGlobal(Offset.zero);
+    final tagSize = renderBox.size;
+    final tagCenter = tagPosition.dy + tagSize.height / 2;
+
+    final screenHeight = MediaQuery.of(context).size.height;
+    final screenCenter = screenHeight / 2;
+
+    final delta = tagCenter - screenCenter;
+    final currentOffset = _scrollController.offset;
+    final targetOffset = (currentOffset + delta)
+        .clamp(0.0, _scrollController.position.maxScrollExtent);
+
+    if ((targetOffset - currentOffset).abs() < 2) return;
+
+    await _scrollController.animateTo(
+      targetOffset,
+      duration: _scrollDuration,
+      curve: Curves.easeOutCubic,
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
     final service = context.watch<AudioService>();
@@ -31,6 +195,10 @@ class PlaylistPage extends StatelessWidget {
           onPressed: () => Navigator.pop(context),
         ),
         actions: [
+          IconButton(
+            icon: Icon(service.playModeIcon, color: Colors.white54),
+            onPressed: service.togglePlayMode,
+          ),
           IconButton(
             icon: const Icon(Icons.clear_all, color: Colors.white54),
             onPressed: () {
@@ -38,29 +206,22 @@ class PlaylistPage extends StatelessWidget {
                 context: context,
                 builder: (context) => AlertDialog(
                   backgroundColor: const Color(0xFF1A1F1E),
-                  title: const Text(
-                    '清空播放列表',
-                    style: TextStyle(color: Colors.white),
-                  ),
-                  content: const Text(
-                    '确定要清空当前播放列表吗？',
-                    style: TextStyle(color: Colors.grey),
-                  ),
+                  title: const Text('清空播放列表',
+                      style: TextStyle(color: Colors.white)),
+                  content: const Text('确定要清空当前播放列表吗？',
+                      style: TextStyle(color: Colors.grey)),
                   actions: [
                     TextButton(
-                      onPressed: () => Navigator.pop(context),
-                      child: const Text('取消'),
-                    ),
+                        onPressed: () => Navigator.pop(context),
+                        child: const Text('取消')),
                     TextButton(
                       onPressed: () {
                         service.clearQueue();
                         Navigator.pop(context);
                         Navigator.pop(context);
                       },
-                      child: const Text(
-                        '清空',
-                        style: TextStyle(color: Colors.red),
-                      ),
+                      child:
+                          const Text('清空', style: TextStyle(color: Colors.red)),
                     ),
                   ],
                 ),
@@ -76,20 +237,13 @@ class PlaylistPage extends StatelessWidget {
                 children: [
                   Icon(Icons.playlist_play, size: 48, color: Colors.grey),
                   SizedBox(height: 16),
-                  Text(
-                    '播放列表为空',
-                    style: TextStyle(color: Colors.grey),
-                  ),
+                  Text('播放列表为空', style: TextStyle(color: Colors.grey)),
                 ],
               ),
             )
           : ListView.builder(
-              padding: const EdgeInsets.only(
-                left: 16,
-                right: 16,
-                top: 8,
-                bottom: UIConstants.miniPlayerBottomSpace,
-              ),
+              controller: _scrollController,
+              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
               itemCount: queue.length,
               itemBuilder: (context, index) {
                 final song = queue[index];
@@ -127,12 +281,14 @@ class PlaylistPage extends StatelessWidget {
                   ),
                   trailing: isCurrent
                       ? Container(
+                          key: _currentTagKey,
                           padding: const EdgeInsets.symmetric(
                             horizontal: 8,
                             vertical: 2,
                           ),
                           decoration: BoxDecoration(
-                            color: const Color(0xFFB8D4D0).withOpacity(0.2),
+                            color:
+                                const Color(0xFFB8D4D0).withValues(alpha: 0.2),
                             borderRadius: BorderRadius.circular(4),
                           ),
                           child: const Text(