Seekbar.dart

import 'dart:math';

import 'package:flutter/material.dart';

class SeekBar extends StatefulWidget {
  final Duration duration;
  final Duration position;
  final ValueChanged<Duration> onChanged;
  final ValueChanged<Duration> onChangeEnd;

  SeekBar({
    @required this.duration,
    @required this.position,
    this.onChanged,
    this.onChangeEnd,
  });

  @override
  _SeekBarState createState() => _SeekBarState();
}

class _SeekBarState extends State<SeekBar> {
  double _dragValue;
  bool _dragging = false;

  @override
  Widget build(BuildContext context) {
    final value = min(_dragValue ?? widget.position.inMilliseconds.toDouble(),
        widget.duration.inMilliseconds.toDouble());

    if (_dragValue != null && !_dragging) {
      _dragValue = null;
    }

    return Stack(
      children: [
        Slider(
          min: 0.0,
          max: widget.duration.inMilliseconds.toDouble(),
          value: value,
          onChanged: (value) {
            if (!_dragging) {
              _dragging = true;
            }
            setState(() {
              _dragValue = value;
            });
            if (widget.onChanged != null) {
              widget.onChanged(Duration(milliseconds: value.round()));
            }
          },
          onChangeEnd: (value) {
            if (widget.onChangeEnd != null) {
              widget.onChangeEnd(Duration(milliseconds: value.round()));
            }
            _dragging = false;
          },
        ),
        Positioned(
          right: 16.0,
          bottom: 0.0,
          child: Text(
              RegExp(r'((^0*[1-9]\d*:)?\d{2}:\d{2})\.\d+$')
                      .firstMatch("$_remaining")
                      ?.group(1) ??
                  '$_remaining',
              style: TextStyle(
                color: Color.fromARGB(255, 175, 175, 175)
              ),
          )
        ),
      ],
    );
  }

  Duration get _remaining => widget.duration - widget.position;
}