Question

我刚刚进入Flutter，Dart和Redux。已经关注YouTube视频修改默认的Flutter示例以使用Redux，但它失败了，我仍然很难理解异常并有效地对它们做出反应。这是代码：

import 'package:flutter/material.dart';
import 'package:meta/meta.dart';
import 'package:redux/redux.dart';
import 'package:flutter_redux/flutter_redux.dart';

// following this youtube video: https://youtu.be/X8B-UzqEaWc

void main() => runApp(new MyApp());

@immutable
class AppState {
  final int counter;
  AppState(this.counter);
}

// actions
enum Actions { increment }

// pure function
AppState reducer(AppState prev, action) {
  if(action == Actions.increment) {
    return new AppState(prev.counter + 1);
  }
  return prev;
}

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

class MyHomePage extends StatelessWidget {  

  final store = new Store(reducer, initialState: new AppState(0));

  //print(store.state.counter); <----- Undefined class 'counter'.

  @override
  Widget build(BuildContext context) {
    return new StoreProvider(
      store: store,      
      child: new Scaffold(
        appBar: new AppBar(
          title: new Text("Flutter Redux"),
        ),
        body: new Center(
          child: new Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              new Text(
                'You have pushed the button this many times:',
              ),
              new StoreConnector(
                converter: (store) => store.state.counter,
                builder: (context, counter) => new Text(
                  "$counter",
                  style: Theme.of(context).textTheme.display1,
                  )
              )
            ],
          ),
        ),
        floatingActionButton: new StoreConnector<int, VoidCallback>(
          converter: (store) {
            return () => store.dispatch(Actions.increment);
          },
          builder: (context, callback) => new FloatingActionButton(
            onPressed: callback,
            tooltip: 'Increment',
            child: new Icon(Icons.add),
          ),
        ) 
      ),
    );
  }
}

首先，当我尝试运行它时，我得到一个异常，声明＆＃34; 以下NoSuchMethodError被抛出构建StoreConnector（脏）： I / flutter（20662）：getter＆＃39; store＆＃39;被称为null。＆＃34;。次要问题是为什么代码中突出显示的打印方法无法识别反吸气剂？感谢。

Answer 1

问题在于我将“dart.previewDart2”设置为true，我想在最新的预览版本中可能会搞砸一些东西。一旦我将选项设置为false，一切都运行良好。

详细说明：

获取文件 - ＆gt;偏好 - ＆gt;设置。
在搜索框中输入“dart”。
找到dart.previewDart2设置后，点击左侧的铅笔图标，然后选择“复制到设置”。
在用户设置的右侧，将设置设置为true。

学习Flutter Redux - 这段代码出了什么问题？

1 个答案: