Download file with progress in Dart/Flutter using 'http' package

downloadFile.dart

import 'dart:typed_data';
import 'dart:io';

import 'package:http/http.dart';
import 'package:path_provider/path_provider.dart';


downloadFile(String url, {String filename}) async {
  var httpClient = http.Client();
  var request = new http.Request('GET', Uri.parse(url));
  var response = httpClient.send(request);
  String dir = (await getApplicationDocumentsDirectory()).path;
  
  List<List<int>> chunks = new List();
  int downloaded = 0;
  
  response.asStream().listen((http.StreamedResponse r) {
    
    r.stream.listen((List<int> chunk) {
      // Display percentage of completion
      debugPrint('downloadPercentage: ${downloaded / r.contentLength * 100}');
      
      chunks.add(chunk);
      downloaded += chunk.length;
    }, onDone: () async {
      // Display percentage of completion
      debugPrint('downloadPercentage: ${downloaded / r.contentLength * 100}');
      
      // Save the file
      File file = new File('$dir/$filename');
      final Uint8List bytes = Uint8List(r.contentLength);
      int offset = 0;
      for (List<int> chunk in chunks) {
        bytes.setRange(offset, offset + chunk.length, chunk);
        offset += chunk.length;
      }
      await file.writeAsBytes(bytes);   
      return;       
   });
  });
}

ineed to use the value to preview on the screen with progress bar any idea how to do it

@A7md-Elkassas
You can use a setState instead where I have given written a debugPrint in the code to store the percentage on a state variable, which you can pass as an argument to a widget.

thank you for answering i have a code for uploading but when i press upload button the percentage inceases if it's 100 its increases to 200
content of uploading function

var url = Uri.parse("http://192.168.1.3/file_upload.php");
    var request = http.MultipartRequest("POST", url);
    request.files.add(http.MultipartFile.fromBytes('file', _pickedFile,
        filename: input.files.first.name));
    var send = request.send();
    send.asStream().listen((http.StreamedResponse r) {
      r.stream.listen((List<int> chunk) {
      
        actualPercentage = percentage / r.contentLength * 100;
        print(r.contentLength);

        chunks.add(chunk);
        percentage += chunk.length;
      }, onDone: () async {
        // Display percentage of completion
        actualPercentage = percentage / r.contentLength * 100;
        if (percentage < 100) {
          setState(() {
            uploadMsg = 'uploading ${actualPercentage.toString()}%';
          });
        } else {
          setState(() {
            uploadMsg = 'Successfully Uploaded';
          });
        }
      });
    });

variables

double actualPercentage = 0;
  double percentage = 0;
  String uploadMsg = '';

 List<List<int>> chunks = new List();

This really should stream the chunks into the file as it goes instead of holding them in memory.

How to implement error handling? I tried implementing onError: (handleError), where i try to show a snackbar if download fails due to loss of internet connection ,but its not working.

@flutternoob My solution was to wrap the entire thing in an try/catch