fix(player): 修复拖动进度条时加载态闪烁

lib/pages/player/widgets/seek_progress_bar.dart

@@ -44,22 +44,94 @@ class SeekProgressBar extends StatefulWidget {
 }
 
 class _SeekProgressBarState extends State<SeekProgressBar> {
+  static const _bufferDebounce = Duration(milliseconds: 350);
+
   final _previewFraction = ValueNotifier<double?>(null);
+  Timer? _bufferTimer;
+  bool _buffering = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _attachSource();
+  }
 
   @override
   void didUpdateWidget(covariant SeekProgressBar oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.valueListenable != widget.valueListenable) {
+      _detachSource(oldWidget.valueListenable);
       _previewFraction.value = null;
+      _bufferTimer?.cancel();
+      _bufferTimer = null;
+      _buffering = false;
+      _attachSource();
     }
   }
 
   @override
   void dispose() {
+    _detachSource(widget.valueListenable);
+    _bufferTimer?.cancel();
     _previewFraction.dispose();
     super.dispose();
   }
 
+  void _attachSource() {
+    widget.valueListenable?.addListener(_handleSourceChanged);
+    _syncBufferState(notify: false);
+  }
+
+  void _detachSource(ValueListenable<VideoPlayerValue>? source) {
+    source?.removeListener(_handleSourceChanged);
+  }
+
+  void _handleSourceChanged() => _syncBufferState();
+
+  void _syncBufferState({bool notify = true}) {
+    final source = widget.valueListenable;
+    if (source == null) {
+      _bufferTimer?.cancel();
+      _bufferTimer = null;
+      _setBuffering(false, notify: notify);
+      return;
+    }
+    final value = source.value;
+    if (!value.isInitialized) {
+      _bufferTimer?.cancel();
+      _bufferTimer = null;
+      _setBuffering(true, notify: notify);
+      return;
+    }
+    if (!value.isBuffering) {
+      _bufferTimer?.cancel();
+      _bufferTimer = null;
+      _setBuffering(false, notify: notify);
+      return;
+    }
+    if (_buffering || _bufferTimer != null) return;
+    _bufferTimer = Timer(_bufferDebounce, () {
+      _bufferTimer = null;
+      final current = widget.valueListenable;
+      if (!mounted ||
+          current != source ||
+          !current!.value.isInitialized ||
+          !current.value.isBuffering) {
+        return;
+      }
+      _setBuffering(true);
+    });
+  }
+
+  void _setBuffering(bool buffering, {bool notify = true}) {
+    if (_buffering == buffering) return;
+    if (!notify || !mounted) {
+      _buffering = buffering;
+      return;
+    }
+    setState(() => _buffering = buffering);
+  }
+
   Future<void> _finish(double fraction, Duration duration) async {
     final source = widget.valueListenable;
     _previewFraction.value = fraction;
@@ -93,7 +165,8 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
 
   Widget _buildTrack(BuildContext context, VideoPlayerValue video) {
     final total = video.duration.inMilliseconds;
-    final loading = !video.isInitialized || video.isBuffering;
+    final scrubbing = _previewFraction.value != null;
+    final loading = !scrubbing && (!video.isInitialized || _buffering);
     final enabled = video.isInitialized && total > 0 && widget.onSeek != null;
     final played = total > 0
         ? (video.position.inMilliseconds / total).clamp(0.0, 1.0)
@@ -102,7 +175,6 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
     final previewPosition = _previewFraction.value == null
         ? video.position
         : seekPositionForFraction(fraction, video.duration);
-    final scrubbing = !loading && _previewFraction.value != null;
     final trackHeight = widget.compact
         ? (scrubbing ? 3.0 : 1.5)
         : (scrubbing ? 4.0 : 3.0);