WingCH

  Future<Uint8List> _downloadImage() async {
    String dir = (await getApplicationDocumentsDirectory()).path;
    File file = new File('$dir/$_filename');

    if (file.existsSync()) {
      var image = await file.readAsBytes();
      return image;
    } else {
      var response = await http.get(_url,);
      var bytes = response.bodyBytes;