我刚刚开始使用 Redux 并尝试实现一个简单的 MERN 应用程序(用于练习)。 我的代码中的所有内容都运行良好,但我的 reducer 函数显示出意外行为。当一个 Action (从 express api 获取数据)被调用时,我的 reducer 正确地转到了特定的开关案例数据日志,但是默认案例被传递了三次,我记录的组件上的数据显示为空。请帮忙。 这是我的代码:-
index.js
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import { BrowserRouter as Router } from 'react-router-dom';
import { Provider } from 'react-redux';
import thunk from 'redux-thunk';
import { createStore, applyMiddleware, combineReducers } from 'redux';
import articlesReducer from './store/reducers/articlesReducer';
import registerServiceWorker from './registerServiceWorker';
const rootReducer = combineReducers({
articles: articlesReducer
});
const store = createStore(rootReducer, applyMiddleware(thunk));
const app = (
<Provider store={store}>
<Router>
<App />
</Router>
</Provider>
);
ReactDOM.render(app, document.getElementById('root'));
registerServiceWorker();
App.js
import React, {Component} from 'react';
import {Switch, Route} from 'react-router-dom';
import './App.css';
import Home from './components/Home/Home';
class App extends Component {
render() {
return (
<div>
<Switch>
<Route exact path="/" component={Home} />
</Switch>
</div>
);
}
}
export default App;
文章.js
export const getAllArticles = () => {
return dispatch => {
return (
fetch('http://localhost:5000/api/articles')
.then(res => res.json())
.then(data => {
dispatch({type: 'GET_ALL_ARTICLES', articles: data})
})
);
};
};
articlesReducer.js
const initialState = {
articles:null
};
const reducer = (state = initialState, action) => {
switch (action.type) {
case 'GET_ALL_ARTICLES':
console.log('in reducer', action.type, action.articles[0]);
return {
...state,
articles: action.articles
};
default:
console.log('In default');
return state;
}
};
export default reducer;
我的组件
import React, { Component } from 'react';
import { connect } from 'react-redux';
import { getAllArticles } from '../../store/actions/articles.js';
class MainPage extends Component {
componentWillMount() {
this.props.initArticles();
console.log(this.props.articles);
}
render() {
return (
<div className="container">
<br />
<h1>Here comes the articles!!</h1>
</div>
);
}
}
const mapStateToProps = state => {
return {
articles: state.articles
};
};
const mapDispatchToProps = dispatch => {
return {
initArticles: () => dispatch(getAllArticles())
};
};
export default connect(mapStateToProps, mapDispatchToProps)(MainPage);
我控制台的输出有点像这样:-
In default
In default
In default
{articles: null}
in reducer GET_ALL_ARTICLES {articles[0] Object}
我不知道是什么错误。提前感谢您的帮助。
最佳答案
我不确定这是否真的是问题所在,但您错误地访问了文章
。你有一个带有 articles
reducer 的 root reducer:
const rootReducer = combineReducers({
articles: articlesReducer
});
初始状态是:
const initialState = {
articles:null
};
并在您的 mapDispatchToProps 中“导入”整个 reducer 状态:
const mapStateToProps = state => {
return {
articles: state.articles
};
};
我想你想访问 articles
属性
const mapStateToProps = state => {
return {
articles: state.articles.articles
};
};
除此之外一切似乎都很好。但是,我会按照评论中的指示将 articles
初始化为空数组 []
。
const initialState = {
articles: []
};
关于javascript - reducer 开关语句不起作用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/49601016/