问题描述
我正在使用MERN和Redux。
我有一个clickHandler函数，该函数调用从我的操作中导入的findAuthor函数。这将通过其ID查找用户并将其返回。我已将用户添加到全局状态。然后，我想检索用户并将其名称添加到本地状态，但是无法正常工作。我不断收到此错误TypeError：this.props.subAuthor未定义。我在这里想念什么？当我尝试仅打印到控制台时，直到第二次单击我才显示任何对象。我如何立即更新？
import React,{ Component } from "react";
import PropTypes from "prop-types";
import GoogleSearch from "./GoogleSearch";
import { connect } from "react-redux";
import { fetchSubjects } from "../../actions/subject";
import { fetchComments } from "../../actions/comment";
import { updateSubject } from "../../actions/subject";
import { getUser } from "../../actions/authActions";
class Subject extends Component {
// on loading the subjects and comments
// are fetched from the database
componentDidMount() {
this.props.fetchSubjects();
this.props.fetchComments();
}
constructor(props) {
super(props);
this.state = {
// set inital state for subjects
// description,summary and comments all invisible
viewDesription: -1,viewSummary: -1,comments: [],name: "",};
}
componentWillReceiveProps(nextProps) {
// new subject and comments are added to the top
// of the arrays
if (nextProps.newPost) {
this.props.subjects.unshift(nextProps.newPost);
}
if (nextProps.newPost) {
this.props.comments.unshift(nextProps.newPost);
}
}
clickHandler = (id) => {
// when a subject title is clicked pass in its id
// and make the description and comments visible
const { viewDescription } = this.state;
this.setState({ viewDescription: viewDescription === id ? -1 : id });
// add relevant comments to the state
var i;
var temp = [];
for (i = 0; i < this.props.comments.length; i++) {
if (this.props.comments[i].subject === id) {
temp.unshift(this.props.comments[i]);
}
}
this.setState({
comments: temp,});
// save the subject id to local storage
// this is done incase a new comment is added
// then the subject associated with it can be retrieved
// and added as a property of that comment
localStorage.setItem("passedSubject",id);
//testing getUser
this.findAuthor(id); // this updates the tempUser in state
this.setState({ name: this.props.subAuthor.name });
};
// hovering on and off subjects toggles the visibility of the summary
hoverHandler = (id) => {
this.setState({ viewSummary: id });
};
hoverOffHandler = () => {
this.setState({ viewSummary: -1 });
};
rateHandler = (id,rate) => {
const subject = this.props.subjects.find((subject) => subject._id === id);
// when no subject was found,the updateSubject won't be called
subject &&
this.props.updateSubject(id,rate,subject.noOfVotes,subject.rating);
alert("Thank you for rating this subject.");
};
// take in the id of the subject
// find it in the props
// get its author id
// call the getUser passing the author id
findAuthor(id) {
console.log("Hitting findAuthor function");
const subject = this.props.subjects.find((subject) => subject._id === id);
const authorId = subject.author;
console.log(authorId);
this.props.getUser(authorId);
}
render() {
const subjectItems = this.props.subjects.map((subject) => {
// if the state equals the id set to visible if not set to invisible
var view = this.state.viewDescription === subject._id ? "" : "none";
var hover = this.state.viewSummary === subject._id ? "" : "none";
var comments = this.state.comments;
var subjectAuthor = this.state.name;
return (
<div key={subject._id}>
<div className="subjectTitle">
<p
className="title"
onClick={() => this.clickHandler(subject._id)}
onMouseEnter={() => this.hoverHandler(subject._id)}
onMouseLeave={() => this.hoverOffHandler()}
>
{subject.title}
</p>
<p className="rate">
Rate this subject:
<button onClick={() => this.rateHandler(subject._id,1)}>
1
</button>
<button onClick={() => this.rateHandler(subject._id,2)}>
2
</button>
<button onClick={() => this.rateHandler(subject._id,3)}>
3
</button>
<button onClick={() => this.rateHandler(subject._id,4)}>
4
</button>
<button onClick={() => this.rateHandler(subject._id,5)}>
5
</button>
</p>
<p className="rating">
Rating: {(subject.rating / subject.noOfVotes).toFixed(1)}/5
</p>
<p className="summary" style={{ display: hover }}>
{subject.summary}
</p>
</div>
<div className="subjectBody " style={{ display: view }}>
<div className="subjectAuthor">
<p className="author">
Subject created by: {subjectAuthor}
<br /> {subject.date}
</p>
</div>
<div className="subjectDescription">
<p className="description">{subject.description}</p>
</div>
<div className="subjectLinks">Links:</div>
<div className="subjectComments">
<p style={{ fontWeight: "bold" }}>Comments:</p>
{comments.map((comment,i) => {
return (
<div key={i} className="singleComment">
<p>
{comment.title}
<br />
{comment.comment}
<br />
Comment by : {comment.author}
</p>
</div>
);
})}
<a href="/addcomment">
<div className="buttonAddComment">ADD COMMENT</div>
</a>
</div>
</div>
</div>
);
});
return (
<div id="Subject">
<GoogleSearch />
{subjectItems}
</div>
);
}
}
Subject.propTypes = {
fetchSubjects: PropTypes.func.isRequired,fetchComments: PropTypes.func.isRequired,updateSubject: PropTypes.func.isRequired,getUser: PropTypes.func.isRequired,subjects: PropTypes.array.isRequired,comments: PropTypes.array.isRequired,newPost: PropTypes.object,subAuthor: PropTypes.object,};
const mapStateToProps = (state) => ({
subjects: state.subjects.items,newSubject: state.subjects.item,comments: state.comments.items,newComment: state.comments.item,subAuthor: state.auth.tempUser[0],});
// export default Subject;
export default connect(mapStateToProps,{
fetchSubjects,fetchComments,updateSubject,// rate subject
getUser,// used for getting author name
})(Subject,Comment);
解决方法
我想为您到目前为止编写的当前代码提供替代解决方案。我知道这不是codereview（除非它实际上是在工作的代码，否则不会在那里讨论），但是，我仍然想向您展示一种划分组件的不同方法。
据我所见，您有许多组件，目前全部打包成一个非常大的组件。从长远来看，这会使事情复杂化，如果可以的话，应该避免这种情况。
正如我从您发布的代码中看到的那样，您确实有几个组成部分，我将它们划分为：
- 主题
- 评论
- 用户
- 评分
- RatingViewer
通过划分现在很大的组件，您可以更轻松地在以后处理一个组件的数据并重用正在制作的组件。您可能想重用其中的某些组件。
出于替代解决方案的目的，我就如何重构代码创建了一个非常快速且基本的演示。这只是一个建议，希望它也可以解决您当前的问题。
您遇到的问题是您想要加载该数据，然后直接使用它。但是，任何提取操作都是异步的，因此在调用this.props.getUser(authorId);之后，您的作者将被添加到您的状态中的某个位置，但是直到完成提取并重新渲染组件后，该作者才可用。
我希望演示中的信息可以为您提供一些见解，虽然可能与您的情况不完全匹配，但是它应该向您表明可以做些什么。
// imports
const { Component } = React;
const { Provider,connect } = ReactRedux;
const { render } = ReactDOM;
const { createStore,combineReducers } = Redux;
// some fake db data
const db = {
comments: [
{ id: 1,subject: 2,user: 2,comment: 'Interesting book' },{ id: 2,user: 3,comment: 'Is interesting the only word you know,you twit' }
],subjects: [
{
id: 1,title: 'Some interesting title',summary: 'Some interesting summary / plot point',author: 2,rate: 0,noOfVotes: 0
},{
id: 2,title: 'Some less interesting title',summary: 'Some more interesting summary / plot point',author: 1,rate: 5,noOfVotes: 2
}
],authors: [
{ id: 1,name: 'John Doe' },name: 'Jane Doe' }
],users: [
{ id: 1,name: 'user 1' },name: 'user 2' },{ id: 3,name: 'user 3' }
]
};
// reducers
const authorReducer = ( state = {},action ) => {
switch (action.type) {
case 'author/add':
return { ...state,[action.payload.id]: action.payload };
default:
return state;
}
};
const userReducer = ( state = {},action ) => {
switch (action.type) {
case 'user/add':
return { ...state,[action.payload.id]: action.payload };
default:
return state;
}
};
const subjectReducer = ( state = {},action ) => {
switch (action.type) {
case 'subject/retrieved':
return Object.assign( {},...action.payload.map( subject => ({ [subject.id]: subject }) ) );
case 'subject/add':
return { ...state,[action.payload.id]: action.payload };
case 'subject/update':
const { id } = action.payload;
return { ...state,[id]: action.payload };
default:
return state;
}
};
const commentReducer = ( state = [],action ) => {
switch (action.type) {
case 'comment/retrieved':
return action.payload.slice();
case 'comments/add':
return [...state,action.payload ];
default:
return state;
}
};
// create the store
const store = createStore( combineReducers({
users: userReducer,authors: authorReducer,comments: commentReducer,subjects: subjectReducer
}) );
// some promise aware fetch methods
const fakeFetch = (entity,filter = null) => {
const entities = db[entity];
return Promise.resolve( (filter ? entities.filter( filter ) : entities).map( e => ({...e}) ) );
}
const fakeUpdate = (entity,id,updatedValue ) => {
const targetEntity = db[entity].find( e => e.id === id );
if (!targetEntity) {
return Promise.reject();
}
Object.assign( targetEntity,updatedValue );
return Promise.resolve( { ...targetEntity } );
}
// separate components
class App extends Component {
render() {
return <Subjects />;
}
}
// subjects component
// cares about retrieving the subjects and displaying them
class SubjectsComponent extends Component {
componentDidMount() {
this.props.fetchSubjects();
}
render() {
const { subjects } = this.props;
if (!subjects || !subjects.length) {
return <div>Loading</div>;
}
return (
<div>
{ subjects.map( subject => <Subject key={subject.id} subject={subject} /> ) }
</div>
);
}
}
// subject component
// displays a subject and fetches the comments for "all" subjects
// this should probably only fetch its own comments,but then reducer has to be changed aswell
// to be aware of that
class SubjectComponent extends Component {
componentDidMount() {
this.props.fetchComments();
}
render() {
const { subject } = this.props;
return (
<div className="subject">
<h1>{ subject.title }<RateView subject={subject} /></h1>
<p>{ subject.summary }</p>
<Rate subject={subject} />
<h2>Comments</h2>
{ this.props.comments && this.props.comments.map( comment => <Comment key={comment.id} comment={comment} /> ) }
</div>
);
}
}
// Just displays a comment and a User component
const Comment = ({ comment }) => {
return (
<div className="comment">
<p>{ comment.comment }</p>
<User id={comment.user} />
</div>
);
}
// User component
// fetches the user in case he hasn't been loaded yet
class UserComponent extends Component {
componentDidMount() {
if (!this.props.user) {
this.props.fetchUser( this.props.id );
}
}
render() {
return <span className="user">{ this.props.user && this.props.user.name }</span>;
}
}
// shows the current rating of a post
const RateView = ({ subject }) => {
if (subject.noOfVotes === 0) {
return <span className="rating">No rating yet</span>;
}
const { rate,noOfVotes } = subject;
return <span className="rating">Total rating { (rate / noOfVotes).toFixed(1) }</span>;
}
// enables voting on a subject,can be triggered once per rendering
// this should truly be combined with the user who rated the subject,but it's a demo
class RateComponent extends Component {
constructor() {
super();
this.onRateClicked = this.onRateClicked.bind( this );
this.state = {
hasRated: false,rateValue: -1
};
}
onRateClicked( e ) {
const userRate = parseInt( e.target.getAttribute('data-value') );
const { subject } = this.props;
this.setState({ hasRated: true,rateValue: userRate },() => {
this.props.updateRate( { ...subject,rate: subject.rate + userRate,noOfVotes: subject.noOfVotes + 1 } );
});
}
render() {
if (this.state.hasRated) {
return <span className="user-rate">You rated this subject with { this.state.rateValue }</span>;
}
return (
<div>
{ [1,2,3,4,5].map( value => <button type="button" onClick={ this.onRateClicked } data-value={value} key={value}>{ value }</button> ) }
</div>
);
}
}
// connecting all the components to the store,with their states and dispatchers
const Subjects = connect(
state => ({ subjects: Object.values( state.subjects ) }),dispatch => ({
fetchSubjects() {
return fakeFetch('subjects').then( result => dispatch({ type: 'subject/retrieved',payload: result }) );
}
}))( SubjectsComponent );
// ownProps will be used to filter only the data required for the component that it is using
const Subject = connect(
(state,ownProps) => ({ comments: state.comments.filter( comment => comment.subject === ownProps.subject.id ) }),dispatch => ({
fetchComments() {
return fakeFetch('comments' ).then( result => dispatch({ type: 'comment/retrieved',payload: result }) );
}
}))( SubjectComponent );
const User = connect(
(state,ownProps) => ({ user: state.users[ownProps.id] }),dispatch => ({
fetchUser( id ) {
return fakeFetch('users',user => user.id === id).then( result => dispatch({ type: 'user/add',payload: result[0] }) );
}
}))( UserComponent );
const Rate = connect( null,dispatch => ({
updateRate( updatedSubject ) {
return fakeUpdate('subjects',updatedSubject.id,updatedSubject).then( updated => dispatch({ type: 'subject/update',payload: updated }) );
}
}))( RateComponent );
// bind it all together and run the app
const targetElement = document.querySelector('#container');
render( <Provider store={store}><App /></Provider>,targetElement );.user {
font-style: italic;
font-size: .9em;
}
.comment {
padding-left: 10px;
background-color: #efefef;
border-top: solid #ddd 1px;
}
h1,h2 {
font-size: .8em;
line-height: .9em;
}
.rating {
padding: 5px;
display: inline-block;
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