如何使用状态而不是设置超时?

Question

我正在学习反应，并决定尝试创建一个排序可视化工具。我从气泡排序开始，几乎成功地创建了一个基本的可视化工具。setTimeout是我用来应用可视化的主要功能。

我觉得在setTimeout上中继没有充分利用反应，我想尝试不同的方法，使用useState钩子应用可视化以及更改状态时发生的重新渲染。我知道useState钩子是异步的，不会立即反映。

这是我的代码：

import React, { useContext, useState, useEffect } from 'react';
const NUMBER_OF_ELEMENTS = 10;
const DEFAULT_COLOR = 'black';
const randomIntFromInterval = (min, max) => {
return Math.floor(Math.random() * (max - min + 1) + min);
}
const Dummy = () => {
const [arr, setArr] = useState([]);
const [numberOfElements, setNumberOfElements] = useState(NUMBER_OF_ELEMENTS);
const [doneElements, setDoneElements] = useState([]);
useEffect(() => {
resetArray();
}, []);
const resetArray = () => {
const arr1 = [];
for(let i = 0; i < numberOfElements; i++)
{
arr1[i] = randomIntFromInterval(5, 100);
}
console.log(arr1);
setArr(arr1);
}
const bubbleSort = (arr, n) => {
let i, j, temp, swapped, delay = 1;
for(i = 0; i < n - 1; i++) 
{
swapped = false;
for(j = 0; j < n - i - 1; j++) 
{
createColor(j, j + 1, delay++, 'darkred');
if(arr[j] > arr[j + 1]) 
{
// swap arr[j] and arr[j+1] 
temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
swapped = true;
createAnimation(j, j + 1, delay++);
}
createColor(j, j + 1, delay++, 'black');
}
createSingleColor(n - i - 1, delay++, 'green');
// If no two elements were  
// swapped by inner loop, then break 
if(swapped === false) break;
}
for(let k = 0; k < n - i - 1; k++) {
createSingleColor(k, delay++, 'green');
}
}
const createAnimation = (one, two, delay) => {
const arrayBars = document.getElementsByClassName('array-bar');
setTimeout(() => {
const barOneHeight = arrayBars[one].style.height;
const barTwoHeight = arrayBars[two].style.height;
arrayBars[two].style.height = `${barOneHeight}`;
arrayBars[one].style.height = `${barTwoHeight}`;
}, 250 * delay);
}
const createColor = (one, two, delay, color) => {
const arrayBars = document.getElementsByClassName('array-bar');
setTimeout(() => {
arrayBars[two].style.backgroundColor = color;
arrayBars[one].style.backgroundColor = color;
}, 250 * delay); 
}
const createSingleColor = (index, delay, color) => {
const arrayBars = document.getElementsByClassName('array-bar');
setTimeout(() => {
arrayBars[index].style.backgroundColor = color;
}, 250 * delay); 
}
const handleSort = (arr) => {
bubbleSort(arr, arr.length);
}
const handlerRange = (e) => {
setNumberOfElements(e.target.value);
}
return (
<div>
<div className="array-container">
{arr.map((value, idx) => (
<div className="array-bar"
key={idx}
style={{
backgroundColor: 'black',
height: `${value}px`,
width: `${100 / arr.length}%`,
display: 'inline-block',
margin: '0 1px'
}}>
</div>
))}
</div>
<div className="buttons-container">
<button onClick={() => handleSort(arr)}>Sort!</button>
<button onClick={() => resetArray()}>Reset</button>
<button onClick={() => {
setDoneElements([...doneElements, 7]);
console.log(doneElements);}}>print</button>
</div>
<div className="slider-container">
1
<input type="range" 
min="1" 
max="100" 
onChange={(e) => handlerRange(e)} 
className="slider" 
id="myRange" 
/>
100
</div>
{numberOfElements}
</div>
);
}
export default Dummy;

例如，当我尝试在bubblesort函数中使用setDoneElements时，我搞砸了可视化效果。

有没有办法使用钩子来应用可视化，而不是那么依赖setTimeout？

Answer 1

找到了一个解决方案：

import React, { useState, useEffect } from 'react';
const shortid = require('shortid');
const randomIntFromInterval = (min, max) => {
return Math.floor(Math.random() * (max - min + 1) + min);
}
const Dummy2 = () => {
const [arr, setArr] = useState([]);
const [length, setLength] = useState(10);
const [doneElements, setDoneElements] = useState([]);
const [compareElements, setCompareElements] = useState([]);
useEffect(() => {
generateArray();
}, [length]);
const generateArray = () => {
setDoneElements([]);
setCompareElements([]);
const tempArr = [];
for(let i = 0; i < length; i++) {
tempArr.push(randomIntFromInterval(7, 107));
}
setArr([...tempArr]);
}
const handleLength = (e) => {
setLength(e.target.value);
}
const bubbleSort = () => {
let i, j, swapped, delay = 100;
const tempArr = [...arr];
const tempDoneElements = [...doneElements];
for(i = 0; i < length - 1; i++) 
{
swapped = false;
for(j = 0; j < length - i - 1; j++) 
{
createColor([j, j + 1], delay, 'COMPARE');
delay += 100;
if(tempArr[j] > tempArr[j + 1]) 
{
createAnimation(tempArr, j, j + 1, delay);
delay += 100;
swapped = true;
}
createColor([], delay, 'NONE');
delay += 100;
}
tempDoneElements.push(length - i - 1);
createColor(tempDoneElements, delay, 'DONE');
delay += 100;
// If no two elements were  
// swapped by inner loop, then break 
if(swapped === false) break;
}
for(let k = 0; k < length - i - 1; k++) {
tempDoneElements.push(k);
}
createColor(tempDoneElements, delay, 'DONE');
delay += 100;
}
const createAnimation = (tempArr, indexOne, indexTwo, delay) => {
const temp = tempArr[indexOne];
tempArr[indexOne] = tempArr[indexTwo];
tempArr[indexTwo] = temp;
const newArr = [...tempArr];
setTimeout(() => {
setArr([...newArr]);
}, delay);
}
const createColor = (tempElements, delay, action) => {
switch(action) {
case 'DONE': 
const newDoneElements = [...tempElements];
setTimeout(() => {
setDoneElements([...newDoneElements]);
}, delay);
break;
case 'COMPARE':
setTimeout(() => {
setCompareElements([...tempElements]);
}, delay);
break;
default:
setTimeout(() => {
setCompareElements([]);
}, delay);
}
}
const maxVal = Math.max(...arr);

return (
<div>
<div className="array-container" style={{height: '50%'}}>
{arr.map((value, idx) => (
<div className="array-element"
key={shortid.generate()}
style={{height: `${(value * 100 / maxVal).toFixed()}%`,
width: `calc(${100 / length}% - 2px)`,
margin: '0 1px',
display: 'inline-block',
backgroundColor: compareElements.includes(idx) ? 'darkred' : 
doneElements.includes(idx) ? 'green' : 'black',
color: 'white'}}
></div>))
}
</div>
<div>
<button onClick={() => generateArray()}>New array</button>
<button onClick={() => bubbleSort()}>Sort</button>
</div>
<div className="slider-container">
1
<input type="range" 
min="1" 
max="100" 
onChange={(e) => handleLength(e)} 
className="slider" 
id="myRange" 
/>
100
</div>
{length}
</div>
);
}
export default Dummy2;

我没有弄乱 DOM，而是使用状态来跟踪更改，因此 react 将负责更改事物。

在排序函数中操作数组时，我们需要记住arr是状态的一部分，因此它是不可变的。 我们需要对副本进行任何更改，并在正确的时间应用更改，以便动画发生，这就是我在createAnimation函数中所做的。

为了跟踪我添加到状态的颜色doneElements和compareElements.每当一个元素到达它的最终位置时，它的索引就会被添加到doneElements。在任何给定时间，只比较两个元素，因此compareElements将只包含两个元素或不包含。