Download Files inside Listview | View Downloaded Files Flutter

dio:
path_provider:
progress_dialog:
simple_permissions:
flutter_full_pdf_viewer: ^1.0.6

import 'dart:io';

import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'package:flutter_full_pdf_viewer/full_pdf_viewer_scaffold.dart';
import 'package:path_provider/path_provider.dart';
import 'package:progress_dialog/progress_dialog.dart';
import 'package:simple_permissions/simple_permissions.dart';

void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue, //primary theme color
      ),
      home: FileDownload(), //call to homepage class
    );
  }
}
class FileDownload extends StatefulWidget{
  @override
  _FileDownloadState createState() => _FileDownloadState();
}

class _FileDownloadState extends State<FileDownload> {
  bool isLoading;
  bool _allowWriteFile=false;

  List<Course>courseContent=new List();


  String progress="";
Dio dio;

@override
  void initState() {

    super.initState();
    dio=Dio();
    courseContent.add(Course(title:"Chapter 2",path:"https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap2.pdf"));
    courseContent.add(Course(title:"Chapter 3",path:"https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap3.pdf"));
    courseContent.add(Course(title:"Chapter 4",path:"https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap4.pdf"));
    courseContent.add(Course(title:"Chapter 5",path:"https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap5.pdf"));
    courseContent.add(Course(title:"Chapter 6",path:"https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap6.pdf"));
    courseContent.add(Course(title:"Chapter 7A",path:"https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap7a.pdf"));
  }

  requestWritePermission() async {

    PermissionStatus permissionStatus = await SimplePermissions.requestPermission(Permission.WriteExternalStorage);



    if (permissionStatus == PermissionStatus.authorized) {

      setState(() {

        _allowWriteFile = true;

      });

    }

  }

    Future<String>getDirectoryPath() async
  {
    Directory appDocDirectory = await getApplicationDocumentsDirectory();

    Directory directory= await new Directory(appDocDirectory.path+'/'+'dir').create(recursive: true);

    return directory.path;
  }

  Future downloadFile(String url,path) async {
  if(!_allowWriteFile)
    {

      requestWritePermission();
    }
    try{
      ProgressDialog progressDialog=ProgressDialog(context,type: ProgressDialogType.Normal);
      progressDialog.style(message: "Downloading File");
      progressDialog.show();



      await dio.download(url, path,onReceiveProgress: (rec,total){
          setState(() {
            isLoading=true;
            progress=((rec/total)*100).toStringAsFixed(0)+"%";
            progressDialog.update(message: "Dowloading $progress");
          });

      });
      progressDialog.hide();

    }catch( e)
    {

      print(e.toString());
    }
  }
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
      backgroundColor: Colors.white70,
      appBar: AppBar(title: Text("FIle Download"),backgroundColor: Colors.red,),
      body: Container(
        child: ListView.builder(itemBuilder: (context,index){
          String url =courseContent[index].path;
          String title =courseContent[index].title;
          String extension=url.substring(url.lastIndexOf("/"));
          return Padding(
            padding: const EdgeInsets.all(8.0),
            child: Card(
              elevation: 10,
              child: Padding(
                padding: const EdgeInsets.all(8.0),
                child: Row(
                  mainAxisSize: MainAxisSize.max,
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: [
                    Text("$title",style: TextStyle(fontSize: 26,color: Colors.purpleAccent,fontWeight: FontWeight.bold),),
                    RaisedButton(
                      color: Colors.green,
                      onPressed: (){
                      getDirectoryPath().then((path) {

                        File f=File(path+"$extension");
                        if(f.existsSync())
                        {
                          Navigator.push(context, MaterialPageRoute(builder: (context){
                            return PDFScreen(f.path);
                          }));
                          return;
                        }

                        downloadFile(url,"$path/$extension");
                      });

                    }, child: Text("View",style: TextStyle(fontSize: 16,color: Colors.white),),),

                  ],
                ),
              ),
            ),
          );
        },itemCount: courseContent.length,),
      ),

    );
  }
}
class PDFScreen extends StatelessWidget {
  String pathPDF = "";
  PDFScreen(this.pathPDF);

  @override
  Widget build(BuildContext context) {
    return PDFViewerScaffold(
        appBar: AppBar(
          title: Text("Document"),
          actions: <Widget>[
            IconButton(
              icon: Icon(Icons.share),
              onPressed: () {},
            ),
          ],
        ),
        path: pathPDF);
  }
}

class Course{
  String title;
  String path;
  Course({this.title,this.path});
}