Bar Progress

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

double percentage = 0;

@override
void initState() {
  Timer.periodic(const Duration(milliseconds: 200), (timer) {
    percentage += 5;
    setState(() {});
    if (percentage == 100) timer.cancel();
  });
  super.initState();
}

SizedBox(
  height: 30,
  width: double.infinity,
  child: LayoutBuilder(builder: (context, constraints) {
    return Stack(
      children: [
        Positioned.fill(
          child: Material(
            color: Colors.purple.shade100,
            shape: const StadiumBorder(),
          ),
        ),
        Positioned(
          left: 0,
          height: constraints.maxHeight,
          width: (percentage / 100) * constraints.maxWidth,
          child: const Material(
            color: Colors.purple,
            shape: StadiumBorder(),
          ),
        ),
        Positioned(
          right: 10,
          top: 0,
          bottom: 0,
          child: Center(
            child: Text(
              '${percentage.round()}%',
              textAlign: TextAlign.center,
              style: const TextStyle(
                fontWeight: FontWeight.bold,
                fontSize: 16,
                color: Colors.white,
              ),
            ),
          ),
        ),
      ],
    );
  }),
),