feat(player): 未就绪改由进度条展示加载态

lib/pages/player/widgets/loading_progress_track.dart

@@ -0,0 +1,102 @@
+// Author: fruit.com.cn
+
+import 'package:flutter/material.dart';
+
+import '../../../core/theme/app_colors.dart';
+
+/// 播放未就绪时沿进度轨道循环移动的加载高光。
+class LoadingProgressTrack extends StatefulWidget {
+  const LoadingProgressTrack({
+    super.key = const Key('progress-loading'),
+    required this.height,
+    this.trackColor = Colors.white24,
+    this.highlightColor = AppColors.blue,
+  });
+
+  final double height;
+  final Color trackColor;
+  final Color highlightColor;
+
+  @override
+  State<LoadingProgressTrack> createState() => _LoadingProgressTrackState();
+}
+
+class _LoadingProgressTrackState extends State<LoadingProgressTrack>
+    with SingleTickerProviderStateMixin, WidgetsBindingObserver {
+  late final AnimationController _controller;
+  late final Animation<double> _position;
+
+  @override
+  void initState() {
+    super.initState();
+    _controller = AnimationController(
+      vsync: this,
+      duration: const Duration(milliseconds: 1200),
+    );
+    _position = CurvedAnimation(parent: _controller, curve: Curves.easeInOut);
+    WidgetsBinding.instance.addObserver(this);
+    _syncAnimation();
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    super.didChangeAppLifecycleState(state);
+    _syncAnimation();
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    _controller.dispose();
+    super.dispose();
+  }
+
+  void _syncAnimation() {
+    if (WidgetsBinding.instance.lifecycleState == AppLifecycleState.resumed) {
+      if (!_controller.isAnimating) _controller.repeat();
+    } else {
+      _controller.stop();
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      height: widget.height,
+      child: ClipRRect(
+        borderRadius: BorderRadius.circular(widget.height / 2),
+        child: LayoutBuilder(
+          builder: (context, constraints) {
+            final highlightWidth = constraints.maxWidth * 0.28;
+            final travel = constraints.maxWidth + highlightWidth;
+            return AnimatedBuilder(
+              animation: _position,
+              builder: (context, _) {
+                final left = -highlightWidth + travel * _position.value;
+                return Stack(
+                  fit: StackFit.expand,
+                  children: [
+                    ColoredBox(
+                      key: const Key('progress-loading-track'),
+                      color: widget.trackColor,
+                    ),
+                    Positioned(
+                      left: left,
+                      top: 0,
+                      bottom: 0,
+                      width: highlightWidth,
+                      child: ColoredBox(
+                        key: const Key('progress-loading-highlight'),
+                        color: widget.highlightColor,
+                      ),
+                    ),
+                  ],
+                );
+              },
+            );
+          },
+        ),
+      ),
+    );
+  }
+}