我在自学项目(reddit 克隆)中使用了几种不同的技术:
- react
- react 还原
- 终极版
- react 路由器(v4)
目标:单击帖子的编辑链接时,转到正确的路径并填充编辑表单字段。
我正在使用一个容器来分派(dispatch)一个 Action 并重新呈现更新容器 Prop 内的组件。它看起来像这样:
容器:
class PostContainer extends Component {
componentDidMount() {
debugger;
const {id} = this.props.match.params;
this.props.dispatch(fetchPost(id));
}
render() {
return (
<Post post={this.props.post} editing={this.props.location.state? this.props.location.state.editing : false}/>
);
}
}
const mapStateToProps = (state, ownProps) => {
debugger;
return {
...ownProps,
post: state.post
};
};
export default connect(mapStateToProps)(withRouter(PostContainer));
嵌套的 Post 组件有额外的嵌套组件:
POST 组件:
class Post extends Component {
constructor(props) {
super(props);
this.editToggle = this.editToggle.bind(this);
}
state = {
editing: this.props.location.state ? this.props.location.state.editing : false
};
editToggle() {
this.setState({editing: !this.state.editing});
}
render() {
const {editing} = this.state;
if (editing || this.props.post === undefined) {
return <PostEditForm editToggle={this.editToggle} editing={this.props.editing} post={this.props.post || {}}/>;
}
return (
<div>
<div>
<h2>Title: {this.props.post.title}</h2>
<span>Author: {this.props.post.author}</span>
<br/>
<span>Posted: {distanceInWordsToNow(this.props.post.timestamp)} ago f</span>
<p>Body: {this.props.post.body}</p>
<button type='button' className='btn btn-primary' onClick={() => this.editToggle()}>Make Edit</button>
</div>
<hr/>
<Comments post={this.props.post}></Comments>
</div>
);
}
}
export default withRouter(Post);
在render
第一个函数if
声明,我将更新的 Prop 传递给 <PostEditForm>
.当 PostEditForm 收到 Prop 时,它会重新渲染组件,但组件的状态不会更新。
后编辑表单:
class PostEditForm extends Component {
state = {
timestamp: this.props.post.timestamp || Date.now(),
editing: this.props.editing || false,
body: this.props.post.body || '',
title: this.props.post.title || '',
category: this.props.post.category || '',
author: this.props.post.author || '',
id: this.props.post.id || uuid()
};
clearFormInfo = () => {
this.setState({
timestamp: Date.now(),
body: '',
title: '',
category: '',
author: '',
id: uuid(),
editing: false
});
};
handleOnChange = (e) => {
this.setState({[e.target.id]: e.target.value});
};
handleSubmit = event => {
event.preventDefault();
const post = {
...this.state
};
if(this.state.editing) {
this.props.dispatch(updatePostAPI(post));
this.setState({
editing: false
})
} else {
this.props.dispatch(createPostAPI(post));
this.clearFormInfo();
window.location.href = `/${post.category}/${post.id}`;
}
};
render() {
const {editing} = this.state;
return (
<form onSubmit={this.handleSubmit}>
<div>
<h2>Create New Post</h2>
<label htmlFor='text'>
Title:
<input
type="text"
onChange={this.handleOnChange}
value={this.state.title}
placeholder="Enter Title"
required
id="title"
name="title"
/>
</label>
<label>
Author:
<input
type="text"
onChange={this.handleOnChange}
value={this.state.author}
placeholder="Enter Author"
required
id="author"
name="author"
/>
</label>
<label>
</label>
<label>
Body:
<textarea
type="text"
onChange={this.handleOnChange}
value={this.state.body}
placeholder="Enter Body"
required
id="body"
name="body"
/>
</label>
</div>
<label>
Category:
<select id = 'category' onChange={this.handleOnChange} value={this.state.value} required>
<option value='Select Category'>Select Category</option>
<option value='react'>react</option>
<option value='redux'>redux</option>
<option value='udacity'>udacity</option>
</select>
</label>
<button type='submit'>Create Post</button>
</form>
);
}
}
export default connect()(PostEditForm);
我想我需要调用 setState
并将传递给状态的新 props 赋值,但我不知道使用哪个 lifeCycle 方法。
当我使用 componentDidUpdate
时,类似于:
class PostEditForm extends Component {
componentDidUpdate(prevProps) {
if(this.props.post.id !== prevProps.post.id) {
this.setState({
timestamp: this.props.post.timestamp,
editing: this.props.post.editing,
title: this.props.post.title,
category: this.props.post.category,
author: this.props.post.author,
id: this.props.post.id
})
}
}
.....
componentDidUpdate
解决了最初的问题,但是每当我更新我正在编辑的表单中的内容时,都会调用 lifeclycle 方法,从而消除了对 onChange 处理程序的需要,这是一个好的做法还是我应该使用不同的方法?
最佳答案
只是一个笔记
componentDidUdpate
在每次重新渲染后调用,
componentDidMount
在组件实例化之后调用。
如果您在 componentDidUdpate()
钩子(Hook)中修改您的状态,您将陷入无限循环,因为 setState()
将重新触发 render()
以及 componentDidUpdate()
如果您在 componentDidMount()
中修改您的状态,此 Hook 只会在实例化后调用一次,而不是每次重新渲染时都会调用,因此后续更新将无法正常工作。
然而问题出在这里:
state = {
timestamp: this.props.post.timestamp || Date.now(),
editing: this.props.editing || false,
body: this.props.post.body || '',
title: this.props.post.title || '',
category: this.props.post.category || '',
author: this.props.post.author || '',
id: this.props.post.id || uuid()
};
render() {
const {editing} = this.state;
//change to const {editing} = this.props;
....
}
您声明状态的方式不适用于将来的更新,一旦实例化完成,状态将指向 Prop 的值,只是定义不可变的原始值。
你应该在整个 PostEditForm
render()
方法中引用 this.props
而不是 this.state
你应该没问题。
要更新状态,您应该将回调从父级(在本例中为 Post 组件)传递给 PostEditForm 并在需要时触发它。
关于默认值,我建议使用 Proptypes 库。
类似于:
import React, {Component} from 'react';
import PropTypes from 'prop-types';
class PostEditForm extends Component {
//your business logic
}
PostEditForm.propTypes = {
timestamp: Proptypes.Object,
editing: PropTypes.bool,
body: PropTypes.string,
title: PropTypes.string,
category: PropTypes.string,
author: PropTypes.string,
id: PropTypes.string
}
PostEditForm.defaultProps = {
timestamp: Date.now(),
editing: false,
body: '',
title: '',
category: '',
author: '',
id: uuid()
}
关于javascript - 在嵌套组件中更新状态的正确方法,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/49862793/