react 组件传递

状态提升：当两个以上组件使用同一个数据时，将数据提升到父组件中

数据流向： 父组件传递到子组件中

CommentList.js

import React from 'react'
const CommentList = ({comments})=>{
    return(
        <div className="comment-list">
            <label>评论列表</label>
            <ul className="list-group mb-3">
                {
                    comments.map((comment, index) => 
                        <li key={index} className="list-group-item">{comment}</li>
                    )
                }
            </ul>
        </div>
    )
}
export default CommentList

CommentBox.js

import React from 'react';
class CommentBox extends React.Component{
    constructor(props){
        super(props)
        this.submitHandle = this.submitHandle.bind(this)
    }
    submitHandle(event){ this.props.onAddComment(this.textInput.value);
        event.preventDefault();
    }
    render() {
        return(
            <form className="p-5" onSubmit={this.submitHandle}>
                <div className="form-group">
                    <label>留言：</label>
                    <input ref={ (textInput) => {this.textInput = textInput}}
                        type="text" 
                        className="form-control" 
                        >
                    </input>
                </div>
                
                <button type="submit" className="btn btn-primary">提交</button>
                <p>已有{this.props.commentsLength}条评论</p>
            </form>
        )
    }
}
export default CommentBox

App.js
 
import CommentBox from './component/CommentBox2'
import CommentList from './component/CommentList'
class App extends Component{
  constructor(props){
    super(props);
    this.state = {
      comments: ["this is the first comment","this is the first comment"]
    }
    this.addComment = this.addComment.bind(this)
  }
  addComment(comment){
    this.setState({
      comments: [...this.state.comments, comment]
    })
  }
  render(){
    const { comments } = this.state;
    return(
      <div className="App">
        <header className="App-header">
            <CommentList comments={comments}></CommentList>
            <CommentBox 
              commentsLength={comments.length}
              onAddComment = {this.addComment}
            ></CommentBox>
        </header>
      </div>
    )
  }
  
}

export default App;