如何解决 React 错误：Cannot read 'Props' of undefined答案

【问题标题】：How to solve the React error: Cannot read 'Props' of undefined如何解决 React 错误：Cannot read 'Props' of undefined
【发布时间】：2020-07-06 01:37:24
【问题描述】：

我正在尝试将名为 react-phone-number-input 的库与我的多步反应表单集成为功能组件，如下所示：

import React, { useState } from "react";
import Helmet from "react-helmet";
import "./reg-style/Credentail.css";
import "react-phone-number-input/style.css";
import PhoneInput from "react-phone-number-input";

export default function Credential() {
  const alter = e => {
    e.preventDefault();
    this.props.nextStep();
  };

  const back = e => {
    e.preventDefault();
    this.props.prevStep();
  };

  const [values, handleChange] = this.props;
  const [value, setValue] = useState();
  return (
    <div>
      <Helmet>
        <body className="form-bg-col" />
      </Helmet>

      <div className="login">
        <div className="reg-container">
          <button onClick={back} className="col-form-prev">
            <i class="fa fa-chevron-left" />
          </button>
          <div className="user-detail email">
            Email:
            <input
              onChange={handleChange("Email")}
              defaultValue={values.Email}
              type="email"
              placeholder="Enter your Email"
            />
          </div>
          <div
            className="user-detail"
            onChange={handleChange("Phone")}
            defaultValue={values.Phone}
          >
            Phone:
            <PhoneInput
              displayInitialValueAsLocalNumber
              placeholder="Enter phone number"
              defaultCountry="IN"
              value={value}
              onChange={setValue}
            />
          </div>
          <div className="user-detail username">
            Username:
            <input
              onChange={handleChange("Username")}
              defaultValue={values.Username}
              type="text"
              placeholder="Select your unique Username"
            />
          </div>
          <div className="user-detail password">
            Password:
            <input
              onChange={handleChange("Password")}
              defaultValue={values.Password}
              type="password"
              placeholder="Choose your Password"
            />
          </div>

          <button onClick={alter} className="col-form-next">
            <i class="fa fa-chevron-right" />
          </button>
        </div>
      </div>
    </div>
  );
}

在运行它时，它会抛出一个错误：

TypeError: Cannot read property 'props' of undefined
Credential
C:/Users/Rahul/Desktop/collegefacemash/src/form/register/Credential.js:78
  75 | import "react-phone-number-input/style.css";
  76 | import PhoneInput from "react-phone-number-input";
  77 | 
> 78 | export default function Credential(props) {
  79 |   const alter = e => {
  80 |     e.preventDefault();
  81 |     this.props.nextStep();

我应该怎么做才能使我的应用程序正常工作？
这个多步骤表单的灵感来自： Multi Step Form With React & Material UI by Traversy Media
你的帮助对我来说非常有价值......

【问题讨论】：

你不要在功能组件中使用this。 reactjs.org/docs/…
又出现同样的错误
你是否从const back = e => { e.preventDefault(); this.props.prevStep(); };中删除了“this”

标签： reactjs react-redux react-props react-state-management react-functional-component

【解决方案1】：

在功能组件上，您不使用 this 关键字。

我更改了您的代码以使其正常工作：

import React, { useState } from "react";
import Helmet from "react-helmet";
import "./reg-style/Credentail.css";
import "react-phone-number-input/style.css";
import PhoneInput from "react-phone-number-input";

export default function Credential(props) {
  const alter = e => {
    e.preventDefault();
    props.nextStep();
  };

  const back = e => {
    e.preventDefault();
    props.prevStep();
  };

  const {values, handleChange} = props;
  const [value, setValue] = useState();
  return (
    <div>
      <Helmet>
        <body className="form-bg-col" />
      </Helmet>

      <div className="login">
        <div className="reg-container">
          <button onClick={back} className="col-form-prev">
            <i class="fa fa-chevron-left" />
          </button>
          <div className="user-detail email">
            Email:
            <input
              onChange={handleChange("Email")}
              defaultValue={values.Email}
              type="email"
              placeholder="Enter your Email"
            />
          </div>
          <div
            className="user-detail"
            onChange={handleChange("Phone")}
            defaultValue={values.Phone}
          >
            Phone:
            <PhoneInput
              displayInitialValueAsLocalNumber
              placeholder="Enter phone number"
              defaultCountry="IN"
              value={value}
              onChange={setValue}
            />
          </div>
          <div className="user-detail username">
            Username:
            <input
              onChange={handleChange("Username")}
              defaultValue={values.Username}
              type="text"
              placeholder="Select your unique Username"
            />
          </div>
          <div className="user-detail password">
            Password:
            <input
              onChange={handleChange("Password")}
              defaultValue={values.Password}
              type="password"
              placeholder="Choose your Password"
            />
          </div>

          <button onClick={alter} className="col-form-next">
            <i class="fa fa-chevron-right" />
          </button>
        </div>
      </div>
    </div>
  );
}

你能看到我做了什么吗？

line 7: added props param
line 10 & 15: removed "this"
line 18: removed "this" and changed from [values, handleChange] to {values, handleChange} in order to destructuring your props object

【讨论】：