根据文件:
componentDidUpdate()在更新发生后立即调用。初始呈现时不调用此方法。
我们可以使用新的useEffect()钩子来模拟componentDidUpdate()，但似乎每次渲染后都会运行useEffect()，甚至是第一次渲染。我如何让它在初始渲染时不运行?
正如你在下面的例子中看到的，componentDidUpdateFunction在初始渲染期间被打印，但是componentDidUpdateClass在初始渲染期间没有被打印。
function ComponentDidUpdateFunction() {
const [count, setCount] = React.useState(0);
React.useEffect(() => {
console.log("componentDidUpdateFunction");
});
return (
<div>
<p>componentDidUpdateFunction: {count} times</p>
<button
onClick={() => {
setCount(count + 1);
}}
>
Click Me
</button>
</div>
);
}
class ComponentDidUpdateClass extends React.Component {
constructor(props) {
super(props);
this.state = {
count: 0,
};
}
componentDidUpdate() {
console.log("componentDidUpdateClass");
}
render() {
return (
<div>
<p>componentDidUpdateClass: {this.state.count} times</p>
<button
onClick={() => {
this.setState({ count: this.state.count + 1 });
}}
>
Click Me
</button>
</div>
);
}
}
ReactDOM.render(
<div>
<ComponentDidUpdateFunction />
<ComponentDidUpdateClass />
</div>,
document.querySelector("#app")
);
<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>
@MehdiDehghani，你的解决方案工作得非常好，你必须做的一件事是卸载，重置didMount。当前值为false。当你试图在其他地方使用这个自定义钩子时，你不会得到缓存值。
import React, { useEffect, useRef } from 'react';
const useDidMountEffect = (func, deps) => {
const didMount = useRef(false);
useEffect(() => {
let unmount;
if (didMount.current) unmount = func();
else didMount.current = true;
return () => {
didMount.current = false;
unmount && unmount();
}
}, deps);
}
export default useDidMountEffect;
@MehdiDehghani，你的解决方案工作得非常好，你必须做的一件事是卸载，重置didMount。当前值为false。当你试图在其他地方使用这个自定义钩子时，你不会得到缓存值。
import React, { useEffect, useRef } from 'react';
const useDidMountEffect = (func, deps) => {
const didMount = useRef(false);
useEffect(() => {
let unmount;
if (didMount.current) unmount = func();
else didMount.current = true;
return () => {
didMount.current = false;
unmount && unmount();
}
}, deps);
}
export default useDidMountEffect;
你可以使用自定义钩子在挂载后运行使用效果。
const useEffectAfterMount = (cb, dependencies) => {
const mounted = useRef(true);
useEffect(() => {
if (!mounted.current) {
return cb();
}
mounted.current = false;
}, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};
以下是typescript版本:
const useEffectAfterMount = (cb: EffectCallback, dependencies: DependencyList | undefined) => {
const mounted = useRef(true);
useEffect(() => {
if (!mounted.current) {
return cb();
}
mounted.current = false;
}, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};
一个简单的方法是创建一个let，在你的组件中并设置为true。
然后说，如果它为真，将其设置为假，然后返回(停止)useEffect函数
像这样:
import { useEffect} from 'react';
//your let must be out of component to avoid re-evaluation
let isFirst = true
function App() {
useEffect(() => {
if(isFirst){
isFirst = false
return
}
//your code that don't want to execute at first time
},[])
return (
<div>
<p>its simple huh...</p>
</div>
);
}
它类似于@Carmine Tambasciabs解决方案，但没有使用状态:)
你可以把它变成自定义钩子，像这样:
import React, { useEffect, useRef } from 'react';
const useDidMountEffect = (func, deps) => {
const didMount = useRef(false);
useEffect(() => {
if (didMount.current) func();
else didMount.current = true;
}, deps);
}
export default useDidMountEffect;
使用的例子:
import React, { useState, useEffect } from 'react';
import useDidMountEffect from '../path/to/useDidMountEffect';
const MyComponent = (props) => {
const [state, setState] = useState({
key: false
});
useEffect(() => {
// you know what is this, don't you?
}, []);
useDidMountEffect(() => {
// react please run me if 'key' changes, but not on initial render
}, [state.key]);
return (
<div>
...
</div>
);
}
// ...
