react项目中使用react-dnd实现列表的拖拽排序功能

import React from 'react'
import Example from './example'
import { DndProvider } from 'react-dnd'
import HTML5Backend from 'react-dnd-html5-backend'
	
class App extends React.Component{
    
    
    handlePreviewList = (previewList) => {
        this.setState({
             previewList
        })
    }
	return (
		<div className="App">
			<DndProvider backend={HTML5Backend}>
				<Example previewList={previewList} 
                    handlePreviewList={this.handlePreviewList}/>
			</DndProvider>
		</div>
	)
}
	
export default App;

import React, { useState } from 'react'
import TopicList from './TopicList';
 
const Container = ({ previewList, handlePreviewList }) => {
    {
        const [topic] = useState(previewList)
        const handleDND = (dragIndex, hoverIndex) => {
            let tmp = previewList[dragIndex] //临时储存文件
            previewList.splice(dragIndex, 1) //移除拖拽项
            previewList.splice(hoverIndex, 0, tmp) //插入放置项
            handlePreviewList(previewList)
        };
        const renderCard = (item, index) => {
            return (
                <TopicList
                    key={item.questionTuid}
                    index={index}
                    id={item.questionTuid}
                    text={item.questionContent}
                    moveCard={handleDND}
                />
            )
        }
        return (
            <div>
                {
                    topic.map((item, i) => renderCard(item, i))
                }
            </div>
        )
    }
}
export default Container

import React, { useRef } from 'react'
import { useDrag, useDrop } from 'react-dnd'
import ItemTypes from './ItemTypes';
const style = {
  padding: '0.5rem 1rem',
  marginBottom: '.5rem',
  backgroundColor: 'white',
  cursor: 'move',
}
const TopicList = ({ id, text, index, moveCard }) => {
  const ref = useRef(null)
  const [, drop] = useDrop({
    //定义拖拽的类型
    accept: ItemTypes.TOPIC,    
    hover(item, monitor) {
      //异常处理判断
      if (!ref.current) { 
        return
      }
      //拖拽目标的Index
      const dragIndex = item.index;
      //放置目标Index
      const hoverIndex = index; 
      // 如果拖拽目标和放置目标相同的话，停止执行
      if (dragIndex === hoverIndex) { 
        return
      }
      //如果不做以下处理，则卡片移动到另一个卡片上就会进行交换，下方处理使得卡片能够在跨过中心线后进行交换.
      //获取卡片的边框矩形
      const hoverBoundingRect = ref.current.getBoundingClientRect();    
      //获取X轴中点
      const hoverMiddleY =
        (hoverBoundingRect.bottom - hoverBoundingRect.top) / 2; 
      //获取拖拽目标偏移量
      const clientOffset = monitor.getClientOffset();   
      const hoverClientY = clientOffset.y - hoverBoundingRect.top
      // 从上往下放置
      if (dragIndex < hoverIndex && hoverClientY < hoverMiddleY) {  
        return
      }
      // 从下往上放置
      if (dragIndex > hoverIndex && hoverClientY > hoverMiddleY) {  
        return
      }
      moveCard(dragIndex, hoverIndex);  //调用方法完成交换
      item.index = hoverIndex;  //重新赋值index，否则会出现无限交换情况
    },
  })
  const [{ isDragging }, drag] = useDrag({
    item: { type: ItemTypes.TOPIC, id, index },
    collect: monitor => ({
      isDragging: monitor.isDragging(),
    }),
  })
  const opacity = isDragging ? 0 : 1
  drag(drop(ref))
  return (
    <div ref={ref} style={{ ...style, opacity }}>
      <span style={{ float: 'left' }}>{index + 1}.</span>
      <div className='stem' dangerouslySetInnerHTML={{ __html: text }}></div>
    </div>
  )
}
export default TopicList

export default {
  TOPIC: 'topic'
}