如何选择文件和图像以使用 flutter web 上传

Question

我想知道如何从用户计算机中选择一张图片到我的 flutter web 应用程序中进行上传

Answer 1

我尝试了下面的代码并且有效。

第一个import 'dart:html';

// variable to hold image to be displayed 

      Uint8List uploadedImage;

//method to load image and update `uploadedImage`


    _startFilePicker() async {
    InputElement uploadInput = FileUploadInputElement();
    uploadInput.click();

    uploadInput.onChange.listen((e) {
      // read file content as dataURL
      final files = uploadInput.files;
      if (files.length == 1) {
        final file = files[0];
        FileReader reader =  FileReader();

        reader.onLoadEnd.listen((e) {
                    setState(() {
                      uploadedImage = reader.result;
                    });
        });

        reader.onError.listen((fileEvent) {
          setState(() {
            option1Text = "Some Error occured while reading the file";
          });
        });

        reader.readAsArrayBuffer(file);
      }
    });
    }

现在只需任何小部件，如按钮并调用方法 _startFilePicker()

Answer 2

我测试了这个包，对结果非常满意 imagePickerWeb 它 returns 3 种不同的类型，可以是图像（用于预览的小部件）、字节、文件（上传)

然后你可以使用它来获取值

html.File _cloudFile;
 var _fileBytes;
 Image _imageWidget;
 
 Future<void> getMultipleImageInfos() async {
    var mediaData = await ImagePickerWeb.getImageInfo;
    String mimeType = mime(Path.basename(mediaData.fileName));
    html.File mediaFile =
        new html.File(mediaData.data, mediaData.fileName, {'type': mimeType});

    if (mediaFile != null) {
      setState(() {
        _cloudFile = mediaFile;
        _fileBytes = mediaData.data;
        _imageWidget = Image.memory(mediaData.data);
      });
    }

正在上传到 firebase

don't forget to add this to your index.html

  <script src="https://www.gstatic.com/firebasejs/7.5.0/firebase-storage.js"></script>

正在上传到 firebase

import 'package:firebase/firebase.dart' as fb;
    uploadToFirebase(File file) async {

    final filePath = 'temp/${DateTime.now()}.png';//path to save Storage
    try {
      fb
          .storage()
          .refFromURL('urlFromStorage')
          .child(filePath)
          .put(file);
    } catch (e) {
      print('error:$e');
    }
  }

如果还有问题，请查看包的文档

Answer 3

不建议直接在 Flutter 中使用 dart:html 包。

改为使用此包：https://pub.dev/packages/file_picker。

Flutter Web 中的使用示例：

class FileUploadButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      child: Text('UPLOAD FILE'),
      onPressed: () async {
        var picked = await FilePicker.platform.pickFiles();

        if (picked != null) {
          print(picked.files.first.name);
        }
      },
    );
  }
}

请注意，Flutter Web 不支持 FilePickerResult.path。

Answer 4

import 'package:http/http.dart' as http;
import 'package:file_picker/file_picker.dart';
import 'package:flutter/material.dart';

class FileUploadWithHttp extends StatefulWidget {
  @override
  _FileUploadWithHttpState createState() => _FileUploadWithHttpState();
}

class _FileUploadWithHttpState extends State<FileUploadWithHttp> {
  PlatformFile objFile = null;

  void chooseFileUsingFilePicker() async {
    //-----pick file by file picker,

    var result = await FilePicker.platform.pickFiles(
      withReadStream:
          true, // this will return PlatformFile object with read stream
    );
    if (result != null) {
      setState(() {
        objFile = result.files.single;
      });
    }
  }

  void uploadSelectedFile() async {
    //---Create http package multipart request object
    final request = http.MultipartRequest(
      "POST",
      Uri.parse("Your API URL"),
    );
    //-----add other fields if needed
    request.fields["id"] = "abc";

    //-----add selected file with request
    request.files.add(new http.MultipartFile(
        "Your parameter name on server side", objFile.readStream, objFile.size,
        filename: objFile.name));

    //-------Send request
    var resp = await request.send();

    //------Read response
    String result = await resp.stream.bytesToString();

    //-------Your response
    print(result);
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Column(
        children: [
          //------Button to choose file using file picker plugin
          RaisedButton(
              child: Text("Choose File"),
              onPressed: () => chooseFileUsingFilePicker()),
          //------Show file name when file is selected
          if (objFile != null) Text("File name : ${objFile.name}"),
          //------Show file size when file is selected
          if (objFile != null) Text("File size : ${objFile.size} bytes"),
          //------Show upload utton when file is selected
          RaisedButton(
              child: Text("Upload"), onPressed: () => uploadSelectedFile()),
        ],
      ),
    );
  }
}

Answer 5

接受的答案确实过时了。就像 jnt 建议的那样，https://pub.dev/packages/file_picker 是一个方便的包，当涉及到使用 Flutter Web 实现图像上传时。

我面临的问题是获取图像的 base64 表示，因为我使用它在 Firestore 中存储图像.正如我们所知，Flutter Web 不支持 dart:io 并抛出 Unsupported operation: _Namespace 错误。因此，使用 File 和读取文件的字节不是一个选项。幸运的是，该软件包提供了 API 将上传的图像转换为 Uint8List。这是我的实现：

import 'package:file_picker/file_picker.dart';

...

FilePickerResult? pickedFile;

...

void chooseImage() async {
    pickedFile = await FilePicker.platform.pickFiles();
    if (pickedFile != null) {
      try {
        setState(() {
          logoBase64 = pickedFile!.files.first.bytes;
        });
      } catch (err) {
        print(err);
      }
    } else {
      print('No Image Selected');
    }
}

如果您需要立即显示本地图像，请使用Image.memory。

Image.memory(logoBase64!);

Answer 6

我也有这个问题；

我使用 https://pub.dev/packages/file_picker 但在 flutter web 路径中不支持；

你应该使用字节；

我将文件字节保存在 var _fileBytes 中并在请求中使用；

var request = http.MultipartRequest('POST', Uri.parse('https://.....com'));
request.headers.addAll(headers);
request.files.add(
   http.MultipartFile.fromBytes(
     'image', 
      await ConvertFileToCast(_fileBytes),
      filename: fileName,
      contentType: MediaType('*', '*')
   )
);
request.fields.addAll(fields);
var response = await request.send();

函数 ConvertFileToCast:

ConvertFileToCast(data){
  List<int> list = data.cast();
  return list;
}

对我有用:)

Answer 7

如果有人想知道如何让它在移动和网络上运行：

var bytes;
      await file!.files.first.readStream!
          .map((asciiValue) => bytes = asciiValue)
          .toList();
      
 FormData body;
 final MultipartFile file = MultipartFile.fromBytes(bytes, filename: "file");
 MapEntry<String, MultipartFile> imageEntry = MapEntry("image", file);
 body.files.add(imageEntry);

如何选择文件和图像以使用 flutter web 上传

How to Pick files and Images for upload with flutter web

dart

flutter

flutter-web