dart - 如何使用 Flutter Web 选择要上传的文件和图像

Question

我想知道如何从用户计算机中选择一个图像到我的颤振网络应用程序中进行上传

Answer 1

我尝试了下面的代码并且它有效。

第一的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);
      }
    });
    }

现在只是任何小部件，如按钮并调用方法_startFilePicker()

Answer 2

dart:html不建议在 Flutter 中直接使用package。

相反，使用这个包：https://pub.dev/packages/file_picker。

如何在 Flutter Web 中使用示例：

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，FilePickerResult.pathFlutter Web 不支持。

Answer 3

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 4

我已经测试了这个包，对结果imagePickerWeb非常满意，它返回 3 种不同的类型，可以是图像（预览小部件）、字节、文件（上传）的形式

那么您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);
      });
    }

上传到火力基地

不要忘记将其添加到您的 index.html

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

上传到火力基地

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');
    }
  }

如果仍有问题，请参阅包的文档

Answer 5

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

我面临的问题是获取图像的base64表示，因为我使用它将图像存储在Firestore中。如我们所知，dart:ioFlutter Web 不支持并抛出Unsupported operation: _Namespace错误。因此，使用File和读取文件的字节不是一种选择。幸运的是，该包提供了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

我也遇到了这个问题;

我使用https://pub.dev/packages/file_picker但在颤动的网络路径中不支持；

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;
}

这对我有用:)