1- certifika yükleme  

void main() {
  HttpOverrides.global = new MyHttpOverrides();
  runApp(const MyApp());
}

class MyHttpOverrides extends HttpOverrides{
  @override
  HttpClient createHttpClient(SecurityContext? context){
    return super.createHttpClient(context)
      ..badCertificateCallback = (X509Certificate cert, String host, int port)=> true;
  }
}

 1- dosya seçme  flutter pub add file_picker

void getSelectedFileName() async {
  final result = await FilePicker.platform
      .pickFiles(allowMultiple: false, type: FileType.any,withData: true);
  if (result == null) return;
  // ploadFiles(result.files);
  ploadFilesHttp(result.files);
}

 2- dosya gönderme dio ile flutter pub add dio

void ploadFiles(List<PlatformFile> platformFiles) async {
  String url = "https://192.168.1.100:45455/api/File/postFile";

  final formData = dio.FormData();

  formData.files.addAll(platformFiles.map((platformFile) =>
      MapEntry(
          'file',
          dio.MultipartFile.fromBytes(platformFile.bytes as List<int>,
              filename: platformFile.name))));

  final response = await dio.Dio().post(url, data: formData);
  print("a");
}

3- dosya gönderme http ile flutter pub add http

void ploadFilesHttp(List<PlatformFile> platformFiles) async {
  String url = "https://192.168.1.100:45455/api/File/postFile";

  final response =
  http.MultipartRequest('POST', Uri.parse(url))

    ..files.addAll(platformFiles.map((file) =>
        http.MultipartFile.fromBytes(
            'file', file.bytes as List<int>,
            filename: file.name)));

  final finalResponse = await response.send();
  print("aaw");
}

3.0.1- dosya gönderme http ile flutter pub add http

void ploadFilesHttp23(List<PlatformFile> platformFiles) async {
  print("aa");
  String url = "https://roketnot.com/upload-profile";

  var headers = <String, String>{
    'Authorization':
    'JWT eyJhbGciOiJaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaCLPNJ748',
  };

  final request = http.MultipartRequest('POST', Uri.parse(url));
  request.headers.addAll(headers);

  platformFiles.forEach((file) async {

    http.MultipartFile multipartFile = await http.MultipartFile.fromPath(
        'apiqueryname', file.path!);

    request.files.add(multipartFile);



    final finalResponse = await request.send();
    print("aaw"+finalResponse.statusCode.toString());

  });

3.1- dosya indirme -> api tarafından stream olarak dönecek. 6'ıncı maddedeki gibi

import 'dart:html' as html;

void getImage() async {
  try {
    var uri = Uri.parse("https://192.168.1.100:45455/api/File/downloadFile");
    final response = await http.post(uri,
      headers: {"Content-Type": "application/json"},
    );
    if (response.contentLength == 0) {
      return;
    }
    final content = base64Encode(response.bodyBytes);

    final anchor = html.AnchorElement(href: 'data:application/octet-stream;base64,$content')
      ..download = "image.rar"
      ..target = 'blank'
       ..click();
  }
  catch (value) {
    print(value);
  }
}

4- .NET CORE TARAFINDAN ALMAK

using Microsoft.AspNetCore.Mvc;

using System.Net;

namespace KaliteApi.Controllers

{

    [Route("api/[controller]")]

    [ApiController]

    public class FileController : ControllerBase

    {

        [Route("postFile")]

        [HttpPost]

        public IActionResult postFile(IFormFile file)

        {

            string url = "ftp://" + "193.111.103.50:32" + "/" + file.FileName;

            FtpWebRequest request = (FtpWebRequest)WebRequest.Create(url);

            request.Credentials = new NetworkCredential("k.ad", "şifre");

            request.Method = WebRequestMethods.Ftp.UploadFile;

            using (Stream ftpStream = request.GetRequestStream())

            {

                file.CopyTo(ftpStream);

            }

            return Ok();

        }

    }

}

5- .NET CORE ftp klasör oluşturma

  private bool CreateFTPDirectory(string directory)

        {

            try

            {

                //create the directory

                string url = "ftp://" + "193.111.103.50:32" + "/" + directory;

                FtpWebRequest requestDir = (FtpWebRequest)FtpWebRequest.Create(new Uri(url));

                requestDir.Method = WebRequestMethods.Ftp.MakeDirectory;

                requestDir.Credentials = new NetworkCredential("k.ad", "şifre");

                requestDir.UsePassive = true;

                requestDir.UseBinary = true;

                requestDir.KeepAlive = false;

                FtpWebResponse response = (FtpWebResponse)requestDir.GetResponse();

                Stream ftpStream = response.GetResponseStream();

                ftpStream.Close();

                response.Close();

                return true;

            }

            catch (WebException ex)

            {

                FtpWebResponse response = (FtpWebResponse)ex.Response;

                if (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable)

                {

                    response.Close();

                    return true;

                }

                else

                {

                    response.Close();

                    return false;

                }

            }

        }

6- .NET CORE ftp dosya indirme

  [Route("downloadFile")]

        [HttpPost]

        public Stream downloadFile()

        {

            string url = "ftp://" + "193.111.103.50:31/hata.png";

            FtpWebRequest request = (FtpWebRequest)FtpWebRequest.Create(new Uri(url));

            request.Credentials = new NetworkCredential("k.ad", "şifre");

            request.Method = WebRequestMethods.Ftp.DownloadFile;

                Stream reader = request.GetResponse().GetResponseStream();

                return reader;

        }