下面我分享我的Flutter代码，只需选择一个图像，并在获得所需的权限后将其显示在屏幕上。然而，代码在Android上运行良好，但当我尝试在Web上上传图像时，会出现MissingPluginException(No implementation found for method requestPermissions on channel flutter.baseflow.com/permissions/methods)异常。

import 'dart:io';

import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:permission_handler/permission_handler.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Project2',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  File _file = File("zz");

  uploadImage() async {
    final ImagePicker _picker = ImagePicker();
    final XFile? image;

    var permissionStatus = requestPermissions();
    if (await permissionStatus.isGranted) {
      image = await _picker.pickImage(source: ImageSource.gallery);
      var selected = File(image!.path);

      setState(() {
        _file = selected;
      });
    } else {
      showToast("Permission not granted");
    }
  }

  Future<PermissionStatus> requestPermissions() async {
    await Permission.photos.request();
    return Permission.photos.status;
  }

  void showToast(String message) {
    Fluttertoast.showToast(
      msg: message,
      toastLength: Toast.LENGTH_SHORT,
      gravity: ToastGravity.BOTTOM,
      timeInSecForIosWeb: 1,
      backgroundColor: Colors.red,
      textColor: Colors.white,
      fontSize: 16.0,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Upload Image"),
      ),
      body: Column(
        children: [
          (_file.path != "zz")
              ? Image.file(_file)
              : Image.asset("assets/img/images.jpeg"),
          SizedBox(
            height: 20,
            width: double.infinity,
          ),
          ElevatedButton(
            onPressed: () => uploadImage(),
            child: Text("Upload"),
          )
        ],
      ),
    );
  }
}

以下是按下upload按钮时生成的堆栈跟踪：

Error: MissingPluginException(No implementation found for method requestPermissions on channel flutter.baseflow.com/permissions/methods)
    at Object.throw_ [as throw] (http://localhost:64931/dart_sdk.js:5041:11)
    at MethodChannel._invokeMethod (http://localhost:64931/packages/flutter/src/services/system_channels.dart.lib.js:943:21)
    at _invokeMethod.next (<anonymous>)
    at http://localhost:64931/dart_sdk.js:37403:33
    at _RootZone.runUnary (http://localhost:64931/dart_sdk.js:37274:59)
    at _FutureListener.thenAwait.handleValue (http://localhost:64931/dart_sdk.js:32530:29)
    at handleValueCallback (http://localhost:64931/dart_sdk.js:33057:49)
    at Function._propagateToListeners (http://localhost:64931/dart_sdk.js:33095:17)
    at _Future.new.[_completeWithValue] (http://localhost:64931/dart_sdk.js:32943:23)
    at async._AsyncCallbackEntry.new.callback (http://localhost:64931/dart_sdk.js:32964:35)
    at Object._microtaskLoop (http://localhost:64931/dart_sdk.js:37526:13)
    at _startMicrotaskLoop (http://localhost:64931/dart_sdk.js:37532:13)
    at http://localhost:64931/dart_sdk.js:33303:9

pubspec.yaml文件：

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  image_picker: ^0.8.3+3
  permission_handler: ^8.1.4+2
  fluttertoast: ^8.0.8

  cupertino_icons: ^1.0.2

dev_dependencies:
  flutter_test:
    sdk: flutter

flutter:
  uses-material-design: true

  assets:
    - assets/img/images.jpeg

PS：flutter clean和flutter run不适用于Web版本。