Linear Progress

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

double percentage = 0;

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

Column(
  children: [
    Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: [
        const Text(
          'Downloading',
          textAlign: TextAlign.center,
          style: TextStyle(
            fontWeight: FontWeight.bold,
            fontSize: 16,
          ),
        ),
        Text(
          '${percentage.round()}%',
          textAlign: TextAlign.center,
          style: const TextStyle(
            fontWeight: FontWeight.bold,
            fontSize: 16,
          ),
        ),
      ],
    ),
    const Gap(8),
    LinearProgressIndicator(
      color: Colors.green,
      minHeight: 30,
      value: percentage / 100,
    ),
  ],
),