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;       
   });
  });
}

you have typo at final Uint8List bytes = Uint8List(r.ntentLength);
and missing }); at the end

@IlyaBlokh, thanks for spotting that, updated.

You're also missing as http in line 4.
It should be import 'package:http/http.dart' as http;.

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

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.

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