hi-client/lib/app/widgets/hi_fixed_scrollbar.dart

import 'package:flutter/material.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';

class HiFixedScrollbar extends StatefulWidget {
  final Widget child;
  final ScrollController controller;

  final bool isShowScrollbar;

  /// 距离右边的间距（默认 18）
  final double right;
  /// 滚动条宽度
  final double thickness;
  /// 滚动条颜色（默认白色 30%）
  final Color thumbColor;
  /// 背景轨道颜色（默认白色 15%）
  final Color trackColor;
  /// 滚动条固定高度（默认 50）
  final double thumbHeight;

  const HiFixedScrollbar({
    super.key,
    required this.child,
    required this.controller,
    this.right = 18,
    this.isShowScrollbar = true,
    this.thickness = 5,
    this.thumbHeight = 50,
    this.thumbColor = const Color.fromRGBO(255, 255, 255, 0.3),
    this.trackColor = const Color.fromRGBO(255, 255, 255, 0.15),
  });

  @override
  State<HiFixedScrollbar> createState() => _HiFixedScrollbarState();
}

class _HiFixedScrollbarState extends State<HiFixedScrollbar> {
  double _thumbOffset = 0.0;

  @override
  void initState() {
    super.initState();
    widget.controller.addListener(_updateThumbPosition);
  }

  void _updateThumbPosition() {
    if (!mounted) return;
    final position = widget.controller.position;
    if (!position.hasPixels || !position.hasContentDimensions) return;

    final maxScrollExtent = position.maxScrollExtent;
    final offset = position.pixels;
    final viewport = position.viewportDimension;

    // ✅ 固定高度滚动条，只根据滚动比例移动位置
    final trackHeight = viewport - widget.thumbHeight;
    final scrollRatio = maxScrollExtent == 0 ? 0 : offset / maxScrollExtent;

    setState(() {
      _thumbOffset = (trackHeight * scrollRatio).clamp(0, trackHeight);
    });
  }

  @override
  void dispose() {
    widget.controller.removeListener(_updateThumbPosition);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (_, constraints) {
        return Stack(
          children: [
            // 滚动内容
            widget.child,

            if(widget.isShowScrollbar)
              ...[
                // 滚动条轨道
                Positioned(
                  right: widget.right.w,
                  top: 0,
                  bottom: 0,
                  child: Container(
                    width: widget.thickness.w,
                    decoration: BoxDecoration(
                      color: widget.trackColor,
                      borderRadius: BorderRadius.circular(4),
                    ),
                  ),
                ),

                // 滚动条拇指
                Positioned(
                  right: widget.right.w,
                  top: _thumbOffset,
                  child: Container(
                    width: widget.thickness.w,
                    height: widget.thumbHeight,
                    decoration: BoxDecoration(
                      color: widget.thumbColor,
                      borderRadius: BorderRadius.circular(4),
                    ),
                  ),
                ),
              ]
          ],
        );
      },
    );
  }
}