未捕获的类型错误:设置状态时无法读取未定义的属性(读取“长度”)
2021-09-15
6442
Uncaught TypeError: Cannot read properties of undefined (reading 'length')
Error is showing in react-dom-development.js file
[1]: https://i.sstatic.net/6a8tF.png
[2]: https://i.sstatic.net/Cn3EP.png
每当我从子组件调用父组件的方法电子邮件处理程序以设置状态时,都会出现上述错误
父组件 :
const loginStates = (
function states() {
return {
email: '',
password: ''
}
}
)
const LoginContainer = () => {
const [state, setState] = useState(loginStates);
const onChangeEmailHandler = (event) => {
setState(prevState => {
return { ...prevState, email: event.target.value }
});
}
return (
<div>
<LoginComponent
onChangeEmailHandler={onChangeEmailHandler}
/>
</div>
)
}
子组件 :
const LoginComponent = props => {
const classes = styles();
const { onChangeEmailHandler } = props;
const [isSignUpPage, setIsSignUpPage] = useState(false);
return (
<React.Fragment>
<TextField
type='text' name='email' id='email' value={state.email}
onChange={(event) =>onChangeEmailHandler(event)}
/>
</React.Fragment>
)
}
3个回答
我找到了导致此错误的原因,原因是:
<React.StrictMode>
标签在
index.js
文件中缺失,当我用
<React.StrictMode> 包装组件后,它就开始工作了。
//In index.js file
ReactDOM.render(
<Provider store={store}>
<React.StrictMode>
<App />
</React.StrictMode>
</Provider>,
document.getElementById('root')
);
Learner
2021-09-16
不要将函数作为状态传递,而应传递对象...
const initialLoginState = {
email: '',
password: ''
}
const LoginContainer = () => {
const [state, setState] = useState(initialLoginState);
TR3
2021-09-15
我无法重现您的错误,但是我对您的代码做了一些更改以使其正常工作,事实证明,为了在 useState 钩子中传递一个函数,您需要传递一个返回所需函数的高阶函数,您可以在 此处 查看完整解释。
父组件 :
import LoginComponent from "./child";
import React, { useState } from "react";
const loginState = function states() {
return {
email: "",
password: ""
};
};
const LoginContainer = () => {
const [state, setState] = useState(() => loginState);
const onChangeEmailHandler = (email) => {
const cur = state();
setState(() => () => ({ ...cur, email }));
};
return (
<div>
<LoginComponent
onChangeEmailHandler={onChangeEmailHandler}
email={state().email} // You need to pass the email here to display it on rerender.
/>
</div>
);
};
export default LoginContainer;
子组件 :
import React from "react";
const LoginComponent = (props) => {
// const classes = styles();
const { onChangeEmailHandler } = props;
// const [isSignUpPage, setIsSignUpPage] = useState(false);
return (
<React.Fragment>
<input
type="text"
name="email"
id="email"
value={props.email} // recieve the email from the props passed from parent.
onChange={(event) => onChangeEmailHandler(event.target.value)}
/>
</React.Fragment>
);
};
export default LoginComponent;
您可以在 此处
查看我的沙盒Mohamed abdelmagid
2021-09-15