问题描述
const Parent = () => {
const customInputRef = useRef(null);
const [customInputVisible,setCustomInputVisible] = useState(false);
async function onPress() {
setCustomInputVisible(true);
await resolvePendingChanged(); // customInput is not null and can be accessed
customInputRef.current.customMethod();
}
return (
<View>
<Button onPress={onPress}>Press me!</Button>
{customInputVisible && <CustomInput ref={customInputRef} />}
</View>
);
}
我看到人们使用 custom forceUpdate function 来触发组件更新,但这对我来说并没有真正的帮助。
在 Svelte 中有这个 "tick" lifecycle hook 正是我需要的。
它返回一个承诺,该承诺在任何挂起状态时立即解决 更改已应用于 DOM(或立即,如果没有 待定状态更改)。
React 中是否有 svelte 的 tick
等价物?如果没有,我如何在 React 中解决这个问题?
解决方法
您可以创建一个使用 callback ref 设置实际引用的自定义钩子,并解析一个承诺:
const { forwardRef,useImperativeHandle,useRef,useState,useCallback,useMemo } = React;
const CustomInput = forwardRef((props,ref) => {
const inputRef = useRef();
useImperativeHandle(ref,() => ({
customMethod: () => {
inputRef.current.focus();
}
}),[]);
return <input ref={inputRef} />;
});
class Deferred {
constructor() {
this.promise = new Promise((resolve,reject) => {
this.resolve = resolve;
this.reject = reject;
});
}
}
const waitForComponent = () => {
const componentRef = useRef(null);
return useMemo(() => {
let deferred = new Deferred();
return {
waitLoad(ref) {
componentRef.current = ref;
if (ref) deferred.resolve();
else deferred = new Deferred(); // create new Promise when ref is null
},isLoaded: () => deferred.promise,componentRef
};
},[]);
}
const Parent = () => {
const { waitLoad,componentRef,isLoaded } = waitForComponent();
const [customInputVisible,setCustomInputVisible] = useState(false);
function onPress() {
setCustomInputVisible(visible => !visible);
// use async here - SO snippet doesn't support async await
isLoaded().then(() => componentRef.current.customMethod());
}
return (
<div>
<button onClick={onPress}>Press me!</button>
{customInputVisible && <CustomInput ref={waitLoad} />}
</div>
);
};
ReactDOM.render(
<Parent />,root
);
<script crossorigin src="https://unpkg.com/react@17/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>
<div id="root"></div>