DownloadNetworkFilesToLocal.dart

import 'dart:io';

import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';

class DownloadFileScreen extends StatefulWidget {
  @override
  _DownloadFileScreenState createState() => _DownloadFileScreenState();
}

class _DownloadFileScreenState extends State<DownloadFileScreen> {
  String filePath;
  int state = 0; //0: Not downloaded, 1: downloading, 2: downloaded

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: ListView(
        children: [
          MyMediaDownloadableWidget('https://placeimg.com/640/480/any', 'any8.png'),
          MyMediaDownloadableWidget('https://placeimg.com/640/480/any', 'any9.png'),
          MyMediaDownloadableWidget('https://placeimg.com/640/480/any', 'any10.png'),
        ],
      )
    );
  }

  filePathSet(path){
    setState(() {
      filePath = path;
    });
  }

  downloadUsingDio(String mediaURL, String fileName, Function filePathSet) async {
    Dio dio = Dio();
    await getApplicationDocumentsDirectory().then((appDir) async {
      if(!File(appDir.path + '/' + fileName).existsSync())
      {
        print('Downloading');
        var filePath = await File(appDir.path + '/' + fileName).create(recursive: true);
        await dio.download(mediaURL, filePath.path);
        filePathSet(filePath.path);
      }
      else{
        print('Already downloaded');
        filePathSet(File(appDir.path + '/' + fileName).path);
      }
    });
  }
}

class MyMediaDownloadableWidget extends StatefulWidget {
  @override
  _MyMediaDownloadableWidgetState createState() => _MyMediaDownloadableWidgetState();

  final String mediaURL;
  final String fileName;

  MyMediaDownloadableWidget(this.mediaURL, this.fileName);
}

class _MyMediaDownloadableWidgetState extends State<MyMediaDownloadableWidget> {
  int currentStatus = 0;
  String filePath;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    downloadUsingDio(widget.mediaURL, widget.fileName, filePathSet);
  }

  @override
  Widget build(BuildContext context) {
    if(currentStatus == 0){
      return ElevatedButton(
          onPressed: (){
            print('download file');
            downloadUsingDio(widget.mediaURL, widget.fileName, filePathSet);
          },
          child: Text('Download')
      );
    } else if(currentStatus == 1){
      return Column(
        children: [
          CircularProgressIndicator()
        ],
      );
    } else {
      return Image.file(File(filePath));
    }
  }

  filePathSet(path){
    setState(() {
      filePath = path;
    });
  }

  downloadUsingDio(String mediaURL, String fileName, Function filePathSet) async {
    Dio dio = Dio();
    setState(() {
      currentStatus = 1;
    });
    await getApplicationDocumentsDirectory().then((appDir) async {
      if(!File(appDir.path + '/' + fileName).existsSync())
      {
        print('Downloading');
        var filePath = await File(appDir.path + '/' + fileName).create(recursive: true);
        await dio.download(mediaURL, filePath.path);
        filePathSet(filePath.path);
        setState(() {
          currentStatus = 2;
        });
      }
      else{
        print('Already downloaded');
        filePathSet(File(appDir.path + '/' + fileName).path);
        setState(() {
          currentStatus = 2;
        });
      }
    });
  }
}