Flutter WEB download option

Question

I am making flutter web app that should generate a file from user data. And have the option to download the output file.

But I can not find any options/packages whic

Answer 1

Simple Code for redirecting to download URL

import 'dart:html' as html;
void downloadFile(String url){
   html.AnchorElement anchorElement =  new html.AnchorElement(href: url);
   anchorElement.download = url;
   anchorElement.click();
}

Answer 2

One way to trigger download is the adapt a common pattern used in "native" javascript, create an anchor element with the download attribute and trigger a click.

import 'dart:convert';
import 'dart:html';

main() {
  File file = // generated somewhere
  final rawData = file.readAsBytesSync();
  final content = base64Encode(rawData);
  final anchor = AnchorElement(
      href: "data:application/octet-stream;charset=utf-16le;base64,$content")
    ..setAttribute("download", "file.txt")
    ..click();
}

Answer 3

Response to bounty:

the case of an audio file it just starts playing rather than downloading it

I've done same thing with video, but I'm sure it will work with audio as well. I assume, your generated audio is an array or blob

    import 'dart:js' as JS;
    import 'dart:html' as HTML;

    const mimeType = 'audio/wav'; // TODO: Pick a right format

    void downloadFile(List chunks) async {
        final blob = HTML.Blob(chunks, mimeType);
        final objectUrl = await HTML.Url.createObjectUrlFromBlob(blob);
        final a = HTML.AnchorElement();
        a.href = item.url;
        a.download = "my_audio_file_${DateTime.now()}.wav";
        HTML.document.body.append(a);
        a.click();
        // Wait for click event to be processed and cleanup
        await Future.delayed(Duration(milliseconds: 100));
        a.remove();
        HTML.Url.revokeObjectUrl(item.videoObjectUrl);
    }

Answer 4

you can use package url_launcher with url_launcher_web

then you can do:

launch("data:application/octet-stream;base64,${base64Encode(yourFileBytes)}")

EDIT: you don't need a plugin if you do this

download.dart:

import 'dart:convert';
// ignore: avoid_web_libraries_in_flutter
import 'dart:html';

void download(
  List<int> bytes, {
  String downloadName,
}) {
  // Encode our file in base64
  final _base64 = base64Encode(bytes);
  // Create the link with the file
  final anchor =
      AnchorElement(href: 'data:application/octet-stream;base64,$_base64')
        ..target = 'blank';
  // add the name
  if (downloadName != null) {
    anchor.download = downloadName;
  }
  // trigger download
  document.body.append(anchor);
  anchor.click();
  anchor.remove();
  return;
}

empty_download.dart:

void download(
  List<int> bytes, {
  String downloadName,
}) {
  print('I do nothing');
}

import and use:

import 'empty_download.dart'
if (dart.library.html) 'download.dart';

void main () {
  download('I am a test file'.codeUnits, // takes bytes
      downloadName: 'test.txt');
}

Answer 5

I've found a solution that let me make an authorized request to get a file (with package http.dart) and then download the file using flutter web (with package dart:html). I don't know if someone other could need this, but I wasn't able to find a solution, so here is the code.

import 'package:http/http.dart';
import 'dart:html' as html;

...

var headers = {
   'Content-Type': 'application/octet-stream',
   'Accept': 'application/octet-stream',
   'Authorization' : 'Bearer [TOKEN HERE]'
};

Response res =
      await get(url, headers: headers); 

if (res.statusCode == 200) {
    final blob = html.Blob([res.bodyBytes]);
    final url = html.Url.createObjectUrlFromBlob(blob);
    final anchor = html.document.createElement('a') as html.AnchorElement
      ..href = url
      ..style.display = 'none'
      ..download = filename;
    html.document.body.children.add(anchor);

    anchor.click();

    html.document.body.children.remove(anchor);
    html.Url.revokeObjectUrl(url);
}

Answer 6

A good workaround is to open the hosted file in a new tab using

import 'dart:html' as html;

openInANewTab(url){
  html.window.open(url, 'PlaceholderName');
}

Fits well for my use case.