我正在使用ReactHooks。我试图在
谢谢!
useEffect
函数中访问User
组件的ref
,但是我得到了null
的值,尽管我将elRef.current
作为第二个参数传递给useEffect
。我应该获得对元素的引用,但在useEffect
之外(函数体外),ref
值可用。为什么?如何在useEffect
内获取elRef.current
值?
代码:import React, { Component, useState, useRef, useEffect } from "react";
const useFetch = url => {
const [data, setData] = useState(null);
const [isLoading, setIsLoading] = useState(false);
const [error, setError] = useState(null);
useEffect(
() => {
setIsLoading(true);
fetch(url)
.then(response => {
if (!response.ok) throw Error(response.statusText);
return response.json();
})
.then(json => {
setIsLoading(false);
setData(json.data);
})
.catch(error => {
setIsLoading(false);
setError(error);
});
},
[url]
);
return { data, isLoading, error };
};
const User = ({ id }) => {
const elRef = useRef(null);
const { data: user } = useFetch(`https://reqres.in/api/users/${id}`);
useEffect(() => {
console.log("ref", elRef.current);
}, [elRef.current]);
if (!user) return null;
return <div ref={elRef}>{user.first_name + " " + user.last_name}</div>;
};
class App extends Component {
state = {
userId: 1
};
handleNextClick = () => {
this.setState(prevState => ({
userId: prevState.userId + 1
}));
};
handlePrevNext = () => {
this.setState(prevState => ({
userId: prevState.userId - 1
}));
};
render() {
return (
<div>
<button
onClick={() => this.handlePrevClick()}
disabled={this.state.userId === 1}
>
Prevoius
</button>
<button onClick={() => this.handleNextClick()}>Next</button>
<User id={this.state.userId} />
</div>
);
}
}
export default App;
Codesandbox链接谢谢!