防止由子组件对父组件数组的更新引起的无限重新渲染

Question

在学生（儿童）组件中

• 当变量的值发生变化时，useEffect 挂钩将通过 handleStudentsChange（父组件提供的函数）更新父数组。

在学生（家长）组件中

• 呈现学生（子级）组件列表
• 为了防止无限循环，handleStudentsChange 函数使用 useCallback 挂钩定义。然而，它似乎不起作用。

问题/疑问

• 一旦发生更改，handleStudentsChange 就会无限运行
• 这是为什么呢？以及如何修复它？
• 注意：我不需要 onSubmit 按钮

请参阅此处的代码： 我是 CodeSandBox 链接

Student.tsx（儿童）

import React, { useState, useEffect, useRef } from "react";
import TextField from "@mui/material/TextField";

interface student {
  firstName: string;
  lastName: string;
  grade: number;
}

interface studentProps {
  id: number;
  firstName: string;
  lastName: string;
  grade: number;
  handleStudentsChange: (index: number, student: student) => void;
}

function Student(props: studentProps) {
  const [firstName, setFirstName] = useState(props.firstName);
  const [lastName, setLastName] = useState(props.lastName);
  const [grade, setGrade] = useState(props.grade);

  useEffect(() => {
    handleStudentsChange(id, {
      firstName: firstName,
      lastName: lastName,
      grade: grade
    });
  }, [firstName, lastName, grade, props]);

  return (
    <>
      <TextField
        label="firstName"
        onChange={(event) => setFirstName(event.target.value)}
        value={firstName}
      />
      <TextField
        label="lastName"
        onChange={(event) => setLastName(event.target.value)}
        value={lastName}
      />
      <TextField
        label="grade"
        onChange={(event) => setGrade(+event.target.value)}
        value={grade}
      />
    </>
  );

Students.tsx（父级）

import React, { useState, useCallback } from "react";
import Student from "./Student";

interface student {
  firstName: string;
  lastName: string;
  grade: number;
}

export default function Students() {
  const [students, setStudents] = useState<student[]>([
    { firstName: "Justin", lastName: "Bieber", grade: 100 },
    { firstName: "Robert", lastName: "Oppenhiemer", grade: 100 }
  ]);

  const handleStudentsChange = useCallback(
    (index: number, updatedStudent: student) => {
      // console.log(index) //I only want this to rerender when the value change however it turn into an infinity loop
      setStudents((prevStudents) => {
        const updatedStudents = [...prevStudents];
        updatedStudents[index] = updatedStudent;
        return updatedStudents;
      });
    },
    []
  );

  return (
    <>
      {students.map((student, index) => {
        return (
          <Student
            key={index}
            id={index}
            firstName={student.firstName}
            lastName={student.lastName}
            grade={student.grade}
            handleStudentsChange={(index: number, newStudent: student) =>
              handleStudentsChange(index, newStudent)
            }
          />
        );
      })}
    </>
  );
}

如上面的代码所示，我尝试在学生（儿童）组件上使用 React.memo ，并在 handleStudentsChange 上使用 useCallback ，希望能够防止无限循环。然而，无限循环仍在继续。

Answer 1

问题

handleStudentsChange不仅在发生更改时无限运行一次-它从第一次渲染开始就无限运行。这是因为Student组件具有调用handleStudentsChange的useEffect，它更新了Students组件中的状态，导致Student组件重新渲染，然后再次调用useEffect，无限循环。

解决方案

您需要在更新输入后才调用handleStudentsChange，而不是在每次渲染后都调用。我在下面的示例中包含了一个示例，它在从输入触发blur事件后更新了Students中的状态。对于更聪明（和复杂）的方法，您可以对比props和state来决定是否需要更新，但我将让您自己解决。

const { Fragment, StrictMode, useCallback, useEffect, useState } = React;
const { createRoot } = ReactDOM;
const { TextField } = MaterialUI;

function Student(props) {
  const [firstName, setFirstName] = useState(props.firstName);
  const [lastName, setLastName] = useState(props.lastName);
  const [grade, setGrade] = useState(props.grade);
  const handleStudentsChange = props.handleStudentsChange;
  
  const onBlur = () => {
    handleStudentsChange(props.id, {
      firstName,
      lastName,
      grade,
    });
  };

  return (
    <Fragment>
      <TextField
        label="firstName"
        onBlur={onBlur}
        onChange={(event) => setFirstName(event.target.value)}
        value={firstName}
      />
      <TextField
        label="lastName"
        onBlur={onBlur}
        onChange={(event) => setLastName(event.target.value)}
        value={lastName}
      />
      <TextField
        label="grade"
        onBlur={onBlur}
        onChange={(event) => setGrade(+event.target.value)}
        value={grade}
      />
    </Fragment>
  );
}

function Students() {
  const [students, setStudents] = useState([
    { firstName: "Justin", lastName: "Bieber", grade: 100 },
    { firstName: "Robert", lastName: "Oppenhiemer", grade: 100 }
  ]);

  const handleStudentsChange = useCallback(
    (index, updatedStudent) => {
      // console.log(index) // I only want this to rerender when the value change however it turn into an infinity loop
      
      console.log({ updatedStudent });

      setStudents((prevStudents) => {
        const updatedStudents = [...prevStudents];
        updatedStudents[index] = updatedStudent;
        return updatedStudents;
      });
    },
    []
  );

  return (
    <Fragment>
      {students.map((student, index) => {
        return (
          <Student
            key={index}
            id={index}
            firstName={student.firstName}
            lastName={student.lastName}
            grade={student.grade}
            handleStudentsChange={(index, newStudent) =>
              handleStudentsChange(index, newStudent)
            }
          />
        );
      })}
    </Fragment>
  );
}

function App() {
  return (
    <div className="App">
      <Students />
    </div>
  );
}

const root = createRoot(document.getElementById("root"));
root.render(<StrictMode><App /></StrictMode>);

<script crossorigin src="https://unpkg.com/react@18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>
<script crossorigin src="https://unpkg.com/@mui/material@latest/umd/material-ui.production.min.js"></script>
<div id="root"></div>