react常用api

1.useReducer---状态管理（类似useState）

一般用于比较复杂的状态管理

import { Button } from "antd";const { useReducer } = require("react");// 1. 定义reducer函数 根据不同的action 返回不同的状态
function reducer(state, action) {switch (action.type) {case "INC":return state + 1;case "DEC":return state - 1;case "SET":return action.payload;default:return state;}
}function App() {// 2. 组件中调用useReducer(reducer，0) => [state，dispatch]// reducer--reducer函数  0--状态初始值const [state, dispatch] = useReducer(reducer, 0);return (<div className="App"><Button type="primary" onClick={() => dispatch({ type: "DEC"})}>-</Button>{state}{/* 3. 调用dispatch({type:'INC}) => 通知reducer产生一个新的状态 使用这个新状态更新UI */}<Button type="primary" onClick={() => dispatch({ type: "INC" })}>+</Button><Button type="primary" onClick={() => dispatch({ type: "SET", payload: 100 })}>update</Button></div>);
}export default App;

2.useMemo

在组件每次重新渲染的时候缓存计算的结果

import { Button } from "antd";
import { useMemo, useState } from "react";// 计算斐波那契数列之和
function fib(n) {if (n < 3) return 1;return fib(n - 2) + fib(n - 1);
}function App() {const [count1, setCount1] = useState(0)useMemo(() => {return fib(count1)})const [count2, setCount2] = useState(0)return (<div className="App">{result}<Button type="primary" onClick={() => setCount1(count1 + 1)}>测试{count1}</Button><Button type="primary" onClick={() => setCount2(count2 + 1)}>测试{count2}</Button></div>);
}export default App;

3.React.memo

允许组件在Props没有改变的情况下跳过渲染-----解决父组件发生变化，子组件在没有的时候，不再重新渲染子组件

React组件的默认渲染机制：只要父组件重新渲染子组件就会重新渲染

import { useMemo, useState } from "react";// 在使用memo缓存组件之后，React会对每一个 prop 使用 Objectis 比较新值和老值，返回true，表示没有变化const MemoSon = memo(function Son({count}) {console.log('子组件发生变化');return <div>son{count}</div>;
})function App() {// 1.简单类型const [count, setCount] = useState(0);// 2.引用类型  比较的是新值和旧值得应用  当父组件函数重新执行时，实际上形成的是新的数组引用// const list = [1, 2, 3]// 3.保证引用稳定useMemo(() => {return [1, 2, 3]}, [])return (<div className="App"><MemoSon count={list} /><button onClick={() => setCount(count + 1)}>+</button></div>);
}export default App;

4.useCallback

在组件多次重新渲染的时候缓存函数

import { useCallback, useState } from "react";const Input = memo(function Input({onChange}) {console.log('子组件发生变化');return <input type="text" onChange={(e) => onChange(e.target.value)} />
})function App() {// 触发父组件重新渲染的函数const [count, setCount] = useState(0);// 穿给子组件的函数const changeHandler = useCallback((value) => console.log(value), []);return (<div className="App"><Input onChange={changeHandler} /><button onClick={() => setCount(count + 1)}>+</button></div>);
}export default App;

5.React.forwardRef

使ref暴露DOM节点给父组件

import { forwardRef, useRef } from "react";const Input = forwardRef((props, ref) => {return <input type="text" ref={ref} />
})function App() {const inputRef = useRef(null)const showRef = () => {console.log(inputRef);inputRef .current.focus();};return (<div className="App"><Input ref={inputRef} /><button onClick={showRef}>focus</button></div>);
}export default App;

6.useInperativeHandle

使ref暴露DOM节点给父组件

import { forwardRef, useRef, useInperativeHandle } from "react";const Input = forwardRef((props, ref) => {const inputRef = useRef(null)// 实现聚焦函数const focusHandler = () => {inputRef.current.focus()}// 暴露函数给父组件使用useInperativeHandle(ref, () => {return {focusHandler}})return <input type="text" ref={inputRef} />
})function App() {const inputRef = useRef(null)const focusHandler = () => {inputRef.current.focusHandler();};return (<div className="App"><Input ref={inputRef} /><button onClick={focusHandler}>focus</button></div>);
}export default App;