问题描述
我正在尝试在我的反应功能组件中使用 useRef,但是当我尝试访问它时出现错误 “类型错误:在使用“useRef”时无法读取未定义的属性“onMonthSelect”。
这是下面的代码
import React,{ useRef,useState,useEffect } from "react";
import moment from "moment";
import "react-dates/initialize";
import "react-dates/lib/css/_datepicker.css";
import { SingleDatePicker } from "react-dates";
const SingleDatePickerComponent = () => {
const monthController = useRef();
const [createdAt,setCreatedAt] = useState(moment());
const onDateChange = (createdAt) => {
console.log(createdAt);
setCreatedAt(createdAt);
};
useEffect(() => {
console.log(monthController);
// Todo: check if month is visible before moving
monthController.current.onMonthSelect(
monthController.current.month,createdAt.format("M")
);
//In this useEffect i am getting the error
},[createdAt]);
return (
<div>
<div style={{ marginLeft: "200px" }}>
</div>
<SingleDatePicker
date={createdAt}
startDateId="MyDatePicker"
onDateChange={onDateChange}
renderMonthElement={(...args) => {
// console.log(args)
monthController.current = {
month: args[0].month,onMonthSelect: args[0].onMonthSelect,};
// console.log(monthController)
return args[0].month.format("MMMM");
}}
id="SDP"
/>
</div>
);
};
export default SingleDatePickerComponent;
解决方法
尚未在初始渲染中设置 ref 值。在访问中使用保护子句或可选链运算符。
useEffect(() => {
// TODO: check if month is visible before moving
monthController.current && monthController.current.onMonthSelect(
monthController.current.month,createdAt.format("M")
);
},[createdAt]);
或
useEffect(() => {
// TODO: check if month is visible before moving
monthController.current?.onMonthSelect(
monthController.current.month,[createdAt]);
提供定义的初始引用值也可能有帮助。
const monthController = useRef({
onMonthSelect: () => {},});