react useRef使用与常见问题
文章目录
- [react useRef使用与常见问题](#react useRef使用与常见问题)
-
- [1. Dom操作: useRef()](#1. Dom操作: useRef())
- [2. 函数组件的转发: React.forwardRef()](#2. 函数组件的转发: React.forwardRef())
- [3. 对普通值进行记忆, 类似于一个class的实例属性](#3. 对普通值进行记忆, 类似于一个class的实例属性)
- [4. 结合useEffect,只在更新时触发](#4. 结合useEffect,只在更新时触发)
- FAQ
1. Dom操作: useRef()
// 1. Dom操作: useRef()
let app = document.querySelector('#app');
let root = ReactDOM.createRoot(app);
let { useState, useEffect, useRef } = React;
let Welcome = (props) => {
const myRef = useRef()
const handleClick = () =>{
myRef.current.focus()
}
return (
<div>
<button onClick={handleClick}>点击</button>
<input ref={myRef} type='text' />
</div>
);
}
let element = (
<Welcome />
);
root.render(element);
2. 函数组件的转发: React.forwardRef()
// 2. 函数组件的转发: React.forwardRef()
let app = document.querySelector('#app');
let root = ReactDOM.createRoot(app);
let { useState, useEffect, useRef, forwardRef } = React;
let Head = forwardRef((props, ref)=> {
return (
<div>
hello Head
{/*将 ref 转发到子组件的input上 */}
<input ref={ref} type='text' />
</div>
)
})
let Welcome = (props) => {
const myRef = useRef()
const handleClick = () =>{
// 点击时候会触发子组件的focus事件
myRef.current.focus()
}
return (
<div>
<button onClick={handleClick}>点击</button>
{/*ref 和组件关联*/}
<Head ref={myRef}></Head>
</div>
);
}
let element = (
<Welcome />
);
root.render(element);
3. 对普通值进行记忆, 类似于一个class的实例属性
// 3. 对普通值进行记忆, 类似于一个class的实例属性
let app = document.querySelector('#app');
let root = ReactDOM.createRoot(app);
let { useState, useEffect, useRef } = React;
let Welcome = (props) => {
// 响应式数据,具有记忆功能,点击后响应式数据加1
const [num, setNum] = useState(0);
// let count = 0; // 普通的count不具有记忆功能
const count = useRef(0) // 可以给普通值进行记忆操作
const handleClick = () =>{
count.current++;
console.log(count.current);
setNum(num + 1)
// console.log(num); // 还是之前的值
}
return (
<div>
<button onClick={handleClick}>点击</button>
</div>
);
}
let element = (
<Welcome />
);
root.render(element);
4. 结合useEffect,只在更新时触发
// 4. 结合useEffect,只在更新时触发
let app = document.querySelector('#app');
let root = ReactDOM.createRoot(app);
let { useState, useEffect, useRef } = React;
let Welcome = (props) => {
// 响应式数据,具有记忆功能,点击后响应式数据加1
const [num, setNum] = useState(0);
const isUpdate = useRef(false)
useEffect(()=>{// 只在点击时候触发
if (isUpdate.current) {
console.log(num);
}
})
const handleClick = () =>{
setNum(num + 1)
isUpdate.current = true
// console.log(num); // 还是之前的值
}
return (
<div>
<button onClick={handleClick}>点击</button>
</div>
);
}
let element = (
<Welcome />
);
root.render(element);
FAQ
https://zh-hans.legacy.reactjs.org/docs/hooks-faq.html#why-am-i-seeing-stale-props-or-state-inside-my-function