我只是进入Flutter,Dart和Redux。已经跟随YouTube视频修改了默认的Flutter示例以使用Redux,但对我来说还是失败了,我仍然很难理解异常并对其做出有效的反应。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),
          ),
        )
      ),
    );
  }
}

因此,首先,当我尝试运行此代码时,我收到一个异常,指出“在构建StoreConnector(dirty)时引发了以下NoSuchMethodError:
I / flutter(20662):将getter'store'调用为null。第二个问题是为什么代码中突出显示的打印方法无法识别计数器 setter/getter ?谢谢。

最佳答案

问题是我将“dart.previewDart2”设置为true,我认为在最新的预览版本中可能搞砸了。将选项设置为false后,一切运行良好。

细节:

  • 转到文件->首选项->设置。
  • 在搜索框中输入“dart”。
  • 找到设置dart.previewDart2后,单击其左侧的铅笔图标,然后选择“复制到设置”。
  • 在用户设置的右侧,将设置设置为true。
  • 关于redux - 学习Flutter Redux-此代码有什么问题?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/49635933/

    10-11 14:57
    查看更多