hooks

• 注意：hooks需要React v16.7.0-alpha以上才支持
• 只能放到function里面
  使用react-dnd注意到package.json有两句

    "peerDependencies": {
        "react": ">= 16.8",
        "react-dom": ">= 16.8"
    }

官方例子

import { useState } from 'react';

function Example() {
  // Declare a new state variable, which we'll call "count"
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

react-dnd

import React, {useCallback, useState} from 'react'
import {DndProvider} from 'react-dnd'
import HTML5Backend from 'react-dnd-html5-backend'
import Container from './Container'

const ImageView = ({src}) => {
  const [hideSourceOnDrag, setHideSourceOnDrag] = useState(true)
  const toggle = useCallback(() => setHideSourceOnDrag(!hideSourceOnDrag), [
    hideSourceOnDrag,
  ])
  return (
    <div className="App">
      <DndProvider backend={HTML5Backend}>
        <div>
          <Container hideSourceOnDrag={hideSourceOnDrag} src={src} />
          <p>
            <label htmlFor="hideSourceOnDrag">
              <input
                id="hideSourceOnDrag"
                type="checkbox"
                checked={hideSourceOnDrag}
                onChange={toggle}
              />
              <small>Hide the source item while dragging</small>
            </label>
          </p>
        </div>
        {src}
      </DndProvider>
    </div>
  )
}

export default ImageView;

import React, { useState } from 'react'
import {useDrag, useDrop} from 'react-dnd'
import update from 'immutability-helper'

const styles = {
  width: '95%',
  height: '90vh',
  position: 'relative',
}

const style = {
  position: 'absolute',
  width: '100%',
  backgroundColor: 'white',
  cursor: 'move',
}

const Box = ({ id, left, top, hideSourceOnDrag, children }) => {
  const [{ isDragging }, drag] = useDrag({
    item: { id, left, top, type: 'box' },
    collect: monitor => ({
      isDragging: monitor.isDragging(),
    }),
  })
  if (isDragging && hideSourceOnDrag) {
    return <div ref={drag} />
  }
  return (
    <div ref={drag} style={{ ...style, left, top }}>
      {children}
    </div>
  )
}

const Container = ({ hideSourceOnDrag, src }) => {
  const [boxes, setBoxes] = useState({
    a: { top: 20, left: 80, title: 'Drag me around' },
  })
  const [, drop] = useDrop({
    accept: 'box',
    drop(item, monitor) {
      const delta = monitor.getDifferenceFromInitialOffset()
      const left = Math.round(item.left + delta.x)
      const top = Math.round(item.top + delta.y)
      moveBox(item.id, left, top)
      return undefined
    },
  })
  const moveBox = (id, left, top) => {
    setBoxes(
      update(boxes, {
        [id]: {
          $merge: { left, top },
        },
      }),
    )
  }
  return (
    <div ref={drop} style={styles}>
      {Object.keys(boxes).map(key => {
        const { left, top, title } = boxes[key]
        return (
          <Box
            key={key}
            id={key}
            left={left}
            top={top}
            hideSourceOnDrag={hideSourceOnDrag}
          >
            {title}
            <img src={src} alt="图片" style={{width:'150%',height:'150%',overflow:'hidden'}} />
          </Box>
        )
      })}
    </div>
  )
}

export default Container