flutter - 选择一个文件并使用 Flutter Web 通过 POST 发送

Question

问题陈述

您好，基本上，我想要的是通过 POST 将文件发送到 python 服务器端 Flask API。

目标是为用户提供一个文件选择器界面，在他/她选择所需的 .txt 文件后，使用 POST 请求通过 Dio 发送它。

一个按钮(Widget)应该调用这个uploadFile()函数，所有的事情都应该由它来处理

---

代码

这是我当前的代码:

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

BaseOptions options = new BaseOptions(
  baseUrl: "http://localhost:5000",
  connectTimeout: 5000,
  receiveTimeout: 3000,
);
InputElement uploadInput = FileUploadInputElement();

void uploadFile() async {
  uploadInput.click();
  uploadInput.onChange.listen((e) {
    // read file content as dataURL
    final files = uploadInput.files;
    final reader = new FileReader();

    if (files.length == 1) {
      final file = files[0];

        reader.onLoad.listen((e) {
          sendFile(reader.result);
        });

        reader.readAsDataUrl(file);
      }
  });
}

sendFile(file) {
  var dio = new Dio(options);
  FormData formData = FormData.fromMap({"file": MultipartFile.fromBytes(file), "fileName": 'data.txt'});
  dio.post('/upload', data: formData);
  //dio.post('/upload', data: FormData.fromMap({'file': 'aaaa'}));
}

---

试验结果

这里的问题是 FileReader没有 readAsBytes 方法，因此我无法使用 fromBytes 方法将文件作为多部分文件发送。

唯一的方法FileReader有:readAsDataUrl、readAsArrayBuffer 和 readAsText我不想阅读 .txt 正文来发送它，我想发送实际文件。

其他尝试

• 我也尝试过使用 file_picker但是好像不支持Flutter Web

引用链接

我的尝试基于:Is there any plugin or way to upload file to server using flutter web?

还有一些我再也找不到了。

React 灵感

我在 React 中设法做到的方式是:

FileUploader.js

export const UploadButton = ({ handler }) => (
    <button onClick={handler.uploadTextFile}>Upload Image</button>
);

export const FileChooser = ({ handler }) => (
    <input
        ref={ref => {
            handler.uploadInput = ref;
        }}
        type="file"
    />
);

Handler.js:

async uploadTextFile(ev) {
        ev.preventDefault();

        this.fileName = uuid.v4();
        const data = new FormData();
        data.append("file", this.uploadInput.files[0]);
        data.append("fileName", this.fileName);
        data.append("setOfWords", this.words);

        await fetch("http://localhost:5000/upload", {
            method: "POST",
            body: data
        });

哭泣

请帮忙？我坚持了 4 天多，还不知道如何在 Flutter Web 中解决这个问题......

Answer 1

设法做到了:

如本 blog post 中所述:

<强>1。我已将 FileReader 读取为 DataUrl

reader.readAsDataUrl(file);

<强>2。对待数据，将其转化为Byte

  Uint8List _bytesData =
      Base64Decoder().convert(file.toString().split(",").last);
  List<int> _selectedFile = _bytesData;

<强>3。要读取它，请使用 Multipart.readFromBytes():

file = http.MultipartFile.fromBytes('file', _selectedFile,
          contentType: new MediaType('application', 'octet-stream'),
          filename: "text_upload.txt")

<强>4。要发送它，请使用 http.request

var url = Uri.parse("http://localhost:5000/upload");
var request = new http.MultipartRequest("POST", url);

request.files.add(http.MultipartFile.fromBytes('file', _selectedFile,
      contentType: new MediaType('application', 'octet-stream'),
      filename: "text_upload.txt"));

request.send().then((response) {
    print("test");
    print(response.statusCode);
    if (response.statusCode == 200) print("Uploaded!");
});

---

最终代码如下所示

import 'dart:convert';
import 'dart:typed_data';
import 'dart:html';
import 'package:http/http.dart' as http;
import 'package:http_parser/http_parser.dart';

InputElement uploadInput = FileUploadInputElement();

void uploadFile() async {
  uploadInput.draggable = true;
  uploadInput.click();
  uploadInput.onChange.listen((e) {
    // read file content as dataURL
    final files = uploadInput.files;
    final reader = new FileReader();

    if (files.length == 1) {
      final file = files[0];

      reader.onLoad.listen((e) {
        sendFile(reader.result);
      });

      reader.readAsDataUrl(file);
    }
  });
}

sendFile(file) {
  var url = Uri.parse("http://localhost:5000/upload");
  var request = new http.MultipartRequest("POST", url);
  Uint8List _bytesData =
      Base64Decoder().convert(file.toString().split(",").last);
  List<int> _selectedFile = _bytesData;

  request.files.add(http.MultipartFile.fromBytes('file', _selectedFile,
      contentType: new MediaType('application', 'octet-stream'),
      filename: "text_upload.txt"));

  request.send().then((response) {
    print("test");
    print(response.statusCode);
    if (response.statusCode == 200) print("Uploaded!");
  });
}