feat: 逻辑与页面布局分离

lib/pages/player/widgets/seek_progress_bar.dart

@@ -37,24 +37,30 @@ class SeekProgressBar extends StatefulWidget {
 }
 
 class _SeekProgressBarState extends State<SeekProgressBar> {
-  double? _previewFraction;
+  final _previewFraction = ValueNotifier<double?>(null);
 
   @override
   void didUpdateWidget(covariant SeekProgressBar oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.valueListenable != widget.valueListenable) {
-      _previewFraction = null;
+      _previewFraction.value = null;
     }
   }
 
+  @override
+  void dispose() {
+    _previewFraction.dispose();
+    super.dispose();
+  }
+
   Future<void> _finish(double fraction, Duration duration) async {
     final source = widget.valueListenable;
-    setState(() => _previewFraction = fraction);
+    _previewFraction.value = fraction;
     try {
       await widget.onSeek?.call(seekPositionForFraction(fraction, duration));
     } finally {
       if (mounted && widget.valueListenable == source) {
-        setState(() => _previewFraction = null);
+        _previewFraction.value = null;
       }
     }
   }
@@ -63,11 +69,18 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
   Widget build(BuildContext context) {
     final source = widget.valueListenable;
     if (source == null) {
-      return _buildTrack(context, const VideoPlayerValue.uninitialized());
+      return ValueListenableBuilder<double?>(
+        valueListenable: _previewFraction,
+        builder: (context, _, _) =>
+            _buildTrack(context, const VideoPlayerValue.uninitialized()),
+      );
     }
     return ValueListenableBuilder<VideoPlayerValue>(
       valueListenable: source,
-      builder: (context, value, _) => _buildTrack(context, value),
+      builder: (context, value, _) => ValueListenableBuilder<double?>(
+        valueListenable: _previewFraction,
+        builder: (context, _, _) => _buildTrack(context, value),
+      ),
     );
   }
 
@@ -77,11 +90,11 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
     final played = total > 0
         ? (video.position.inMilliseconds / total).clamp(0.0, 1.0)
         : 0.0;
-    final fraction = _previewFraction ?? played;
-    final previewPosition = _previewFraction == null
+    final fraction = _previewFraction.value ?? played;
+    final previewPosition = _previewFraction.value == null
         ? video.position
         : seekPositionForFraction(fraction, video.duration);
-    final scrubbing = _previewFraction != null;
+    final scrubbing = _previewFraction.value != null;
 
     return Column(
       mainAxisSize: MainAxisSize.min,
@@ -107,12 +120,12 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
                 value: fraction,
                 onChangeStart: enabled
                     ? (value) {
-                        setState(() => _previewFraction = value);
+                        _previewFraction.value = value;
                         widget.onScrubStart?.call();
                       }
                     : null,
                 onChanged: enabled
-                    ? (value) => setState(() => _previewFraction = value)
+                    ? (value) => _previewFraction.value = value
                     : null,
                 onChangeEnd: enabled
                     ? (value) => unawaited(_finish(value, video.duration))