關於 React 小書：評論功能

Component 規劃

評論功能整架構

向父元件傳遞數據

數據傳遞順序

當使用可點擊發布按鈕，將 CommentInput 的 state 當中最金的數據傳給父組件 ComponentApp，ComponentApp 會把這組數據傳給 CommentList 進行渲染。

如何傳遞數據

CommentInput 如何向 CommentApp 傳遞數據？父組件 CommentApp 只要透過 props 給子組件 CommentInput 傳入一個 callback function，當使用者點擊發布按鈕時，CommentInput 調用 props 中的 callback function 並將 state 傳入該函數即可。

在 CommentApp 中的 CommentInput 傳入 onSubmit 屬性，這個屬性值是 CommentApp 的一個方法 handleSubmitComment。這樣 CommentInput 可調用 this.props.onSubmit(...) 把數據傳給 CommentApp。

React 小書 評論功能

index.js

import React from 'react'
import ReactDOM from 'react-dom'
import CommentApp from './CommentApp'
import './index.css'

ReactDOM.render(
  <CommentApp />,
  document.getElementById('root')
)

CommentApp.js

import React, { Component } from 'react'
import CommentInput from './CommentInput'
import CommentList from './CommentList'

class CommentApp extends Component {
  constructor() {
    super()
    this.state = {
      comments: []
    }
  }

  handleSubmitComment (comment) {
    console.log(comment)
    if (!comment) return
    if (!comment.username) return alert('請輸入使用者名稱')
    if (!comment.content) return alert('請輸入內容')

    this.state.comments.push(comment)
    this.setState({
      comments: this.state.comments
    })
  }

  render() {
    return (
      <div className='wrapper'>
        <CommentInput onSubmit={this.handleSubmitComment.bind(this)}/>
        <CommentList comments={this.state.comments}/>
      </div>
    )
  }
}

export default CommentApp

CommentInput.js

import React, { Component } from 'react'

class CommentInput extends Component {
  constructor() {
    super()
    this.state = {
      username: '',
      content: ''
    }
  }

  handleUsernameChange (event) {
    this.setState({
      username: event.target.value
    })
  }

  handleContentChange (event) {
    this.setState({
      content: event.target.value
    })
  }

  handleSubmit () {
    if (this.props.onSubmit) {
      const { username, content } = this.state
      this.props.onSubmit({username, content})
    }
    this.setState({ content: '' })
  }

  render () {
    return (
      <div className='comment-input'>
        <div className='comment-field'>
          <span className='comment-field-name'>使用者名稱：</span>
          <div className='comment-field-input'>
            <input
              value={this.state.username} 
              onChange={this.handleUsernameChange.bind(this)} />
          </div>
        </div>
        <div className='comment-field'>
          <span className='comment-field-name'>評論內容：</span>
          <div className='comment-field-input'>
            <textarea 
              value={this.state.content}
              onChange={this.handleContentChange.bind(this)} />
          </div>
        </div>
        <div className='comment-field-button'>
          <button onClick={this.handleSubmit.bind(this)}>
            發布
          </button>
        </div>
      </div>
    )
  }
}

export default CommentInput

CommentList.js

import React, { Component } from 'react'
import Comment from './Comment'

class CommentList extends Component {
  static defaultProps = {
    comments: []
  }

  render() {
    // const comments = [
    //   {username: 'Jerry', content: 'Hello'},
    //   {username: 'Tomy', content: 'World'},
    //   {username: 'Lucy', content: 'Good'}
    // ]
    // return (
    //   <div>
    //     {comments.map((comment, i) => 
    //       <Comment comment={comment} key={i} /> )}
    //   </div>
    // )
    return (
      <div>
        {this.props.comments.map((comment, i) =>
          <Comment comment={comment} key={i} />
        )}
      </div>
    )
  }
}

export default CommentList

Comment.js

import React, { Component } from 'react'

class Comment extends Component {
  render () {
    return (
      <div className='comment'>
        <div className='comment-user'>
          <span>{this.props.comment.username} </span>：
        </div>
        <p>{this.props.comment.content}</p>
      </div>
    )
  }
}

export default Comment

index.css

body {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  background-color: #fbfbfb;
}

.wrapper {
  width: 500px;
  margin: 10px auto;
  font-size: 14px;
  background-color: #fff;
  border: 1px solid #f1f1f1;
  padding: 20px;
}

/* 评论框样式 */
.comment-input {
  background-color: #fff;
  border: 1px solid #f1f1f1;
  padding: 20px;
  margin-bottom: 10px;
}

.comment-field {
  margin-bottom: 15px;
  display: flex;
}

.comment-field .comment-field-name {
  display: flex;
  flex-basis: 100px;
  font-size: 14px;
}

.comment-field .comment-field-input {
  display: flex;
  flex: 1;
}

.comment-field-input input,
.comment-field-input textarea {
  border: 1px solid #e6e6e6;
  border-radius: 3px;
  padding: 5px;
  outline: none;
  font-size: 14px;
  resize: none;
  flex: 1;
}

.comment-field-input textarea {
  height: 100px;
}

.comment-field-button {
  display: flex;
  justify-content: flex-end;
}

.comment-field-button button {
  padding: 5px 10px;
  width: 80px;
  border: none;
  border-radius: 3px;
  background-color: #00a3cf;
  color: #fff;
  outline: none;
  cursor: pointer;
}

.comment-field-button button:active {
  background: #13c1f1;
}

/* 评论列表样式 */
.comment-list {
  background-color: #fff;
  border: 1px solid #f1f1f1;
  padding: 20px;
}

/* 评论组件样式 */
.comment {
  display: flex;
  border-bottom: 1px solid #f1f1f1;
  margin-bottom: 10px;
  padding-bottom: 10px;
  min-height: 50px;
}

.comment .comment-user {
  flex-shrink: 0;
}

.comment span {
  color: #00a3cf;
  font-style: italic;
}

.comment p {
  margin: 0;
  /*text-indent: 2em;*/
}

總結

1. 實現功能前先理解、分析需求、劃分組件。劃分組件的基本原則：可複用性、可維護性。
2. 受控組件：若 React.js 中的 <input />, <textarea />, <select /> 等元素的值，如果受到 React.js 控制就是受控組件。
3. 組件之間透過 props 通過父元素傳遞數據的技巧。

參考資源

• 实战分析：评论功能（三）