使用react-dnd编写一个可拖拽排列的list

// ListItem.tsx
import { styled } from '@mui/material/styles';
import * as React from 'react';
import { useDrag } from 'react-dnd';

const StyledListItem = styled('div', {
  shouldForwardProp: prop => prop !== 'isDragging'
})<{ isDragging: boolean }>(({ isDragging, theme }) => ({
  opacity: isDragging ? 0.5 : 1,
  border: '1px blue solid',
}));

const ListItem = () => {
  const [{isDragging}, dragRef] = useDrag(() => ({
    type: 'listItem',
    collect: monitor => ({
      isDragging: !!monitor.isDragging(),
    }),
  }))

  return (
    <StyledListItem ref={dragRef} isDragging={isDragging}>
      list item
    </StyledListItem>
  )
}

export default ListItem;

// SortableList.tsx
import React, { forwardRef } from 'react';
import { useDrop } from 'react-dnd';
import ListItem from './components/listItem';

const SortableList = () => {

  const canMoveItem = () => {
    console.log('canMoveItem')
    return true;    //<--- 具体逻辑后面再写，这里先设为true，即容器内部一直是可以drop的。
  }

  const moveItem = () => {
    console.log('moveItem');    //<--- 具体逻辑后面再写。
  }

  const [{ isOver, canDrop }, dropRef] = useDrop(
    () => ({
      accept: 'listItem',
      canDrop: () => canMoveItem(),
      drop: () => moveItem(),
      collect: (monitor) => ({
        isOver: !!monitor.isOver(),
        canDrop: !!monitor.canDrop()
      })
    }),
    [canMoveItem, moveItem]
  )
  
  return (
    <div>
      isOver: {String(isOver)}<br />
      canDrop: {String(canDrop)}
      <div
        ref={dropRef}
        style={{
          position: 'relative',
          width: '600px',
          height: '400px',
          border: '2px purple solid'
        }}
      >
        <ListItem></ListItem>
      </div>
    </div>
  );
}

export default SortableList;

// ListItem.tsx
// 将list item也变成droppable
const [spec, dropRef] = useDrop({
    accept: 'listItem',
    hover: (item, monitor) => {
        const dragIndex = item.index
        const hoverIndex = index
        const hoverBoundingRect = ref.current?.getBoundingClientRect()
        const hoverMiddleY = (hoverBoundingRect.bottom - hoverBoundingRect.top) / 2
        const hoverActualY = monitor.getClientOffset().y - hoverBoundingRect.top

        // 如果是向下拖，只有当hover的坐标小于自身高度的一半时，继续保持drag，否则相当于要挪动其他的list item，给当前的item腾个地方
        // if dragging down, continue only when hover is smaller than middle Y
        if (dragIndex < hoverIndex && hoverActualY < hoverMiddleY) return
        // 如果是向上拖，只有当hover的坐标大于自身高度的一半时，继续保持drag，否则相当于要挪动其他的list item，给当前的item腾个地方
        if (dragIndex > hoverIndex && hoverActualY > hoverMiddleY) return
        moveListItem(dragIndex, hoverIndex)
        item.index = hoverIndex
    },
});

// ListItem.tsx
const ref = useRef(null);

const dragDropRef = dragRef(dropRef(ref))

// Mock data
const PETS = [
  { id: 1, name: 'dog' },
  { id: 2, name: 'cat' },
  { id: 3, name: 'fish' },
  { id: 4, name: 'hamster' },
]

// SortableList.tsx
const moveListItem = useCallback(
    (dragIndex, hoverIndex) => {
        console.log({dragIndex, hoverIndex})
        const dragItem = pets[dragIndex]
        const hoverItem = pets[hoverIndex]
        // 将PETS数组中，drag的item和hover的item交换位置
        setPets(pets => {
            const updatedPets = [...pets]
            updatedPets[dragIndex] = hoverItem
            updatedPets[hoverIndex] = dragItem
            return updatedPets
        })
    },
    [pets],
)