Reactjs TypeError:无法读取属性';onMonthSelect';使用“未定义”时的;useRef";
我试图在我的react函数组件中使用useRef,但当我试图访问它时,我得到了一个错误 TypeError:使用“useRef”时无法读取未定义的属性“onMonthSelect” 这是下面的代码Reactjs TypeError:无法读取属性';onMonthSelect';使用“未定义”时的;useRef";,reactjs,use-ref,react-dates,Reactjs,Use Ref,React Dates,我试图在我的react函数组件中使用useRef,但当我试图访问它时,我得到了一个错误 TypeError: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, { 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;
import React,{useRef,useState,useffect}来自“React”;
从“时刻”中导入时刻;
导入“反应日期/初始化”;
导入“react dates/lib/css/_datepicker.css”;
从“反应日期”导入{SingleDatePicker};
常量SingleDatePickerComponent=()=>{
const monthController=useRef();
const[createdAt,setCreatedAt]=useState(矩());
const onDateChange=(createdAt)=>{
console.log(createdAt);
setCreatedAt(createdAt);
};
useffect(()=>{
控制台日志(monthController);
//TODO:移动前检查月份是否可见
monthController.current.onMonthSelect(
monthController.current.month,
createdAt.format(“M”)
);
//在这种情况下,我得到了错误
},[createdAt]);
返回(
{
//console.log(args)
monthController.current={
月份:args[0]。月份,
onMonthSelect:参数[0]。onMonthSelect,
};
//控制台日志(monthController)
返回参数[0].month.format(“MMMM”);
}}
id=“SDP”
/>
);
};
导出默认SingleDatePickerComponent;
在初始渲染时还不会设置ref值。在访问上使用guard子句或可选的链接运算符
useEffect(() => {
// TODO: check if month is visible before moving
monthController.current && monthController.current.onMonthSelect(
monthController.current.month,
createdAt.format("M")
);
}, [createdAt]);
或
它还可以帮助提供定义的初始参考值
const monthController = useRef({
onMonthSelect: () => {},
});
const monthController = useRef({
onMonthSelect: () => {},
});