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flutter - “示例”类型不是“示例”的“示例”类型的子类型

问题描述

我开始使用这种语言并尝试创建一个可以从服务器（通过 websocket）接收消息并将它们显示在 ListView 中的应用程序。

我在专用文件中创建了一个类来将此消息转换为实体。

但是，从跟踪来看，我在几个文件中使用的类类型似乎并不......“相同”。

痕迹：

E/flutter ( 9655): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: type 'Example' is not a subtype of type 'Example' of 'example' where
E/flutter ( 9655):   Example is from package:exampleProject/components/Example.dart
E/flutter ( 9655):   Example is from package:exampleProject/components/example.dart
E/flutter ( 9655): 
E/flutter ( 9655): #0      Plugin._onMessageReceived.<anonymous closure> (package:exampleProject/plugin.dart:35:15)
E/flutter ( 9655): #1      Iterable.forEach (dart:core/iterable.dart:279:30)
E/flutter ( 9655): #2      Plugin._onMessageReceived (package:exampleProject/plugin.dart:31:16)
E/flutter ( 9655): #3      WebSocketsNotifications._onReceptionOfMessageFromServer.<anonymous closure> (package:exampleProject/websockets.dart:95:15)
E/flutter ( 9655): #4      Iterable.forEach (dart:core/iterable.dart:279:30)
E/flutter ( 9655): #5      WebSocketsNotifications._onReceptionOfMessageFromServer (package:exampleProject/websockets.dart:94:16)
E/flutter ( 9655): #6      _rootRunUnary (dart:async/zone.dart:1134:38)
E/flutter ( 9655): #7      _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter ( 9655): #8      _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter ( 9655): #9      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:338:11)
E/flutter ( 9655): #10     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:265:7)
E/flutter ( 9655): #11     _ForwardingStreamSubscription._add (dart:async/stream_pipe.dart:134:11)
E/flutter ( 9655): #12     _ForwardingStream._handleData (dart:async/stream_pipe.dart:100:10)
E/flutter ( 9655): #13     _ForwardingStreamSubscription._handleData (dart:async/stream_pipe.dart:166:13)
E/flutter ( 9655): #14     _rootRunUnary (dart:async/zone.dart:1134:38)
E/flutter ( 9655): #15     _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter ( 9655): #16     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter ( 9655): #17     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:338:11)
E/flutter ( 9655): #18     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:265:7)
E/flutter ( 9655): #19     _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:766:19)
E/flutter ( 9655): #20     _StreamController._add (dart:async/stream_controller.dart:642:7)
E/flutter ( 9655): #21     _rootRunUnary (dart:async/zone.dart:1134:38)
E/flutter ( 9655): #22     _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter ( 9655): #23     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter ( 9655): #24     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:338:11)
E/flutter ( 9655): #25     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:265:7)
E/flutter ( 9655): #26     _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:766:19)
E/flutter ( 9655): #27     _StreamController._add (dart:async/stream_controller.dart:642:7)
E/flutter ( 9655): #28     _StreamController.add (dart:async/stream_controller.dart:588:5)
E/flutter ( 9655): #29     new _WebSocketImpl._fromSocket.<anonymous closure> (dart:_http/websocket_impl.dart:1143:21)
E/flutter ( 9655): #30     _rootRunUnary (dart:async/zone.dart:1134:38)
E/flutter ( 9655): #31     _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter ( 9655): #32     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter ( 9655): #33     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:338:11)
E/flutter ( 9655): #34     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:265:7)
E/flutter ( 9655): #35     _SinkTransformerStreamSubscription._add (dart:async/stream_transformers.dart:70:11)
E/flutter ( 9655): #36     _EventSinkWrapper.add (dart:async/stream_transformers.dart:17:11)
E/flutter ( 9655): #37     _WebSocketProtocolTransformer._messageFrameEnd (dart:_http/websocket_impl.dart:336:22)
E/flutter ( 9655): #38     _WebSocketProtocolTransformer.add (dart:_http/websocket_impl.dart:231:46)
E/flutter ( 9655): #39     _SinkTransformerStreamSubscription._handleData (dart:async/stream_transformers.dart:122:24)
E/flutter ( 9655): #40     _rootRunUnary (dart:async/zone.dart:1134:38)
E/flutter ( 9655): #41     _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter ( 9655): #42     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter ( 9655): #43     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:338:11)
E/flutter ( 9655): #44     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:265:7)
E/flutter ( 9655): #45     _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:766:19)
E/flutter ( 9655): #46     _StreamController._add (dart:async/stream_controller.dart:642:7)
E/flutter ( 9655): #47     _StreamController.add (dart:async/stream_controller.dart:588:5)
E/flutter ( 9655): #48     _Socket._onData (dart:io-patch/socket_patch.dart:1831:41)
E/flutter ( 9655): #49     _rootRunUnary (dart:async/zone.dart:1138:13)
E/flutter ( 9655): #50     _CustomZone.runUn

这是我的实体类：

// example.dart

class Example {
  String name;

  Example.fromJson(Map<String, dynamic> decodedJson) {
    name = decodedJson['name'];
  }
}

这是与套接字管理器通信并从中接收消息并将内容转换为实体的插件：

// plugin.dart

import 'dart:convert';

import 'package:flutter/foundation.dart';
import 'package:exampleProject/websockets.dart';
import 'package:exampleProject/components/Example.dart';

Plugin plugin = new Plugin();

class Plugin {
  static final Plugin _plugin = new Plugin._internal();

  factory Plugin() => _plugin;

  Plugin._internal() {
    // Initialize sockets
    sockets.initCommunication();

    sockets.addListener(_onMessageReceived);
  }

  _onMessageReceived(message) {
    Map<String, dynamic> decodedJson = json.decode(message);

    _listeners.forEach((Function callback) {

      // --------------------------------------------------------------< Creating the class instance
      Example example = Example.fromJson(decodedJson);
      // --------------------------------------------------------------< Send it to listeners
      callback(example);
    });
  }

  ObserverList<Function> _listeners = new ObserverList<Function>();

  addListener(Function callback) {
    _listeners.add(callback);
  }

  removeListener(Function callback) {
    _listeners.remove(callback);
  }
}

我的主要：

// main.dart

import 'package:flutter/material.dart';

import 'package:exampleProject/websockets.dart';
import 'package:exampleProject/plugin.dart';
import 'package:exampleProject/components/Example.dart';

void main() => runApp(App());

class App extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> {
  // --------------------------------------------------------------< List
  List<Example> examples = [];

  @override
  void initState() {
    super.initState();

    plugin.addListener(_onMessageReceived);
  }

  @override
  void dispose() {
    plugin.removeListener(_onMessageReceived);
    super.dispose();
  }

  // --------------------------------------------------------------< List insert
  _onMessageReceived(Example example) {
    examples.insert(0, example);
    // Force render
    setState(() {});
  }

  [...]
}

我错过了什么 ？

预先感谢您的帮助

标签： flutterdart

解决方案

这一行：

import 'package:exampleProject/components/Example.dart';

应该：

import 'package:exampleProject/components/example.dart';

因为这就是它的名字。类名是Example但文件名不是。

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