我已经尝试过对此处列出的问题进行其他回答,但它们不起作用。我在做什么不同?
我有一个应用程序,我想在其中列出与之相关的评论列表/评论数组的主题。当用户单击“添加主题”链接时,用户将看到一个随机主题,该主题带有与之相关的过去评论,并且有机会添加新评论。我可以打印出主题,但不能打印出评论。我什至可以在控制台中打印出注释,但不能在页面上打印。
该错误表明注释未定义。我在做什么错了?
代码如下:
topic.js
import React, { Component } from "react";
import axios from "axios";
import { withRouter } from "react-router-dom";
import { createComment, listTopicWithComments } from "../util/APIUtils";
import "./Topic.css";
import TopicComp from "../components/TopicComp";
import { Form, Input, Button, Icon, Select, Col, notification } from "antd";
const URL = "http://localhost:8080/api/auth/randomtopic";
const URL2 = "http://localhost:8080/api/auth/topic/";
const Option = Select.Option;
const FormItem = Form.Item;
const { TextArea } = Input;
class Topic extends Component {
constructor(props) {
super(props);
this.state = {
topic: {},
comment: {
text: ""
}
};
this.handleSubmit = this.handleSubmit.bind(this);
this.isFormInvalid = this.isFormInvalid.bind(this);
this.handleCommentChange = this.handleCommentChange.bind(this);
//this.listTopicWithComments=this.listTopicWithComments.bind(this);
}
handleSubmit(event) {
event.preventDefault();
const commentData = this.state.comment.text;
const commentTopicid = this.state.topic.id;
console.log("commentdata:", commentData);
console.log("topicid: ", commentTopicid);
createComment(commentData, commentTopicid)
.then(response => {
console.log("response comment: ", response.data);
this.props.history.push("/");
})
.catch(error => {
if (error.status === 401) {
this.props.handleLogout(
"/login",
"error",
"You have been logged out. Please login and choose randome topic."
);
} else {
notification.error({
message: "Social-J App",
description: error.message || "Sorry, something went wrong."
});
}
});
listTopicWithComments(commentTopicid).then(response => {
console.log("topic comment", response.data);
this.props.history.push("/");
});
}
validateComment = commentText => {
if (commentText.length === 0) {
return {
validateStatus: "error",
errorMsg: "Please enter your comment!"
};
} else if (commentText.length > 150) {
return {
validateStatus: "error",
errorMsg: `Comment is too long (Maximum 150 characters
allowed)`
};
} else {
return {
validateStatus: "success",
errorMsg: null
};
}
};
handleCommentChange(event) {
const value = event.target.value;
this.setState({
comment: {
text: value,
...this.validateComment(value)
}
});
}
componentDidMount() {
if (this.props.isAuthenticated) {
axios
.get(URL)
.then(response => {
console.log("response", response.data);
this.setState({ topic: response.data });
})
.catch(err => {
console.log(err);
});
}
}
isFormInvalid() {
if (this.state.comment.validateStatus !== "success") {
return true;
}
}
render() {
//console.log("URL used: ",URL);
//console.log("new topic",this.state.topic.id);
//console.log("new topic",this.state.topic.topic);
const topicId = this.state.topic.id;
const uDate = this.state.topic.expirationDateTime;
const oldComments = this.state.topic.comments;
console.log("topicid: ", topicId);
console.log("date: ", uDate);
console.log("oldcomments: ", oldComments);
//return nComment;
return (
<div className="new-comment-container">
<h1 className="page-title">{this.state.topic.topic}</h1>
<div>
{this.state.topic.comments.map(comment => {
return <div key={comment.id}>{comment.comment}</div>;
})}
</div>
<div className="new-comment-content">
<Form
onSubmit={this.handleSubmit}
className="create-
comment-form"
>
<FormItem
validateStatus={this.state.comment.validateStatus}
help={this.state.comment.errorMsg}
className="comment-form-row"
>
<TextArea
placeholder="Enter comment"
style={{
fontSize: "16px"
}}
autosize={{ minRows: 3, maxRows: 6 }}
name="comment"
value={this.state.comment.text}
onChange={this.handleCommentChange}
/>
</FormItem>
<FormItem className="comment-form-row">
<Button
type="primary"
htmlType="submit"
size="large"
disabled={this.isFormInvalid()}
className="create-comment-form-button"
>
Add Comment
</Button>
</FormItem>
</Form>
</div>
<div>hi</div>
</div>
);
}
}
export default withRouter(Topic);
这是错误。 TypeError:
this.state.topic.comments是未定义的渲染 client / src / components / Topic.js:134
131 | <div className="new-comment-container">
132 | <h1 className="page-title">{this.state.topic.topic}</h1>
133 | <div>
> 134 | {this.state.topic.comments.map(comment =>{
135 | return <div key={comment.id}>
136 | {comment.comment}
137 | </div>
答案 0 :(得分:2)
您正在尝试加载this.state.topic.comments
之前使用topic
。
您可以例如首先将主题设置为null
,然后从渲染返回null
,直到它被设置为止。
示例
class Topic extends Component {
constructor(props) {
super(props);
this.state = {
topic: null,
comment: {
text: ""
}
};
this.handleSubmit = this.handleSubmit.bind(this);
this.isFormInvalid = this.isFormInvalid.bind(this);
this.handleCommentChange = this.handleCommentChange.bind(this);
}
render() {
const { topic } = this.state;
if (topic === null) {
return null;
}
// ...
}
}