从0开始，手把手教你使用React开发答题App

项目演示地址

项目源码

其他版本教程

项目代码结构

前言

React 框架的优雅不言而喻，组件化的编程思想使得React框架开发的项目代码简洁，易懂，但早期 React 类组件的写法略显繁琐。React Hooks 是 React 16.8 发布以来最吸引人的特性之一，她简化了原有代码的编写，是未来 React 应用的主流写法。

本文通过一个实战小项目，手把手从零开始带领大家快速入门React Hooks。本项目线上演示地址：

在本项目中，会用到以下知识点：

React 组件化设计思想
React State 和 Props
React 函数式组件的使用
React Hooks useState 的使用
React Hooks useEffect 的使用
React 使用 Axios 请求远程接口获取问题及答案
React 使用Bootstrap美化界面

Hello React

（1）安装node.js 官网链接

（2）安装vscode 官网链接

（3）安装 creat-react-app 功能组件，该组件可以用来初始化一个项目，即按照一定的目录结构，生成一个新项目。

打开cmd 窗口输入：

npm install --g create-react-app

npm install --g yarn

（-g 代表全局安装）

如果安装失败或较慢。需要换源，可以使用淘宝NPM镜像，设置方法为：

npm config set registry https://registry.npm.taobao.org

设置完成后，重新执行

npm install --g create-react-app

npm install --g yarn

（4）在你想创建项目的目录下例如 D:/project/ 打开cmd命令输入

create-react-app react-exam

去使用creat-react-app命令创建名字是react-exam的项目

安装完成后，移至新创建的目录并启动项目

cd react-exam

yarn start

一旦运行此命令，localhost:3000新的React应用程序将弹出一个新窗口。

项目目录结构

右键react-exam目录，使用vscode打开该目录。

react-exam项目目录中有一个/public和/src目录，以及node_modules，.gitignore，README.md，和package.json。

在目录/public中，重要文件是index.html，其中一行代码最重要

<div id="root"></div>

该div做为我们整个应用的挂载点

/src目录将包含我们所有的React代码。

要查看环境如何自动编译和更新您的React代码，请找到文件/src/App.js：

将其中的

        <a

          className="App-link"

          href="https://reactjs.org"

          target="_blank"

          rel="noopener noreferrer"

        >

          Learn React

        </a>

修改为

        <a

          className="App-link"

          href="https://reactjs.org"

          target="_blank"

          rel="noopener noreferrer"

        >

          和豆约翰 Learn React

        </a>

保存文件后，您会注意到localhost:3000编译并刷新了新数据。

React-Exam项目实战

1. 首页制作

1.安装项目依赖，在package.json中添加：

  "dependencies": {

    "@testing-library/jest-dom": "^4.2.4",

    "@testing-library/react": "^9.3.2",

    "@testing-library/user-event": "^7.1.2",

    "react": "^16.13.1",

    "react-dom": "^16.13.1",

    "react-scripts": "3.4.1",

    "axios": "^0.19.2",

    "bootstrap": "^4.5.0",

    "he": "^1.2.0",

    "react-loading": "^2.0.3",

    "reactstrap": "^8.4.1"

  },

执行命令：

yarn install

修改index.js，导入bootstrap样式

import "bootstrap/dist/css/bootstrap.min.css";

修改App.css代码

html {

  width: 80%;

  margin-left: 10%;

  margin-top: 2%;

}

.ansButton {

  margin-right: 4%;

  margin-top: 4%;

}

修改App.js,引入Quiz组件

import React from 'react';

import './App.css'

import { Quiz } from './Exam/Quiz';

function App() {

  return (

    <div className = 'layout'>

    <Quiz></Quiz>

    </div>

  );

}

export default App;

在项目src目录下新增Exam目录，Exam目录中新建Quiz.js

Quiz组件的定义如下：

Quiz.js，引入开始页面组件Toggle。

import React, { useState } from "react";

import { Toggle } from "./Toggle";

export const Quiz = () => {

  const [questionData, setQuestionData] = useState([]);

  const questions = questionData.map(({ question }) => [question]);

  const answers = questionData.map(({ incorrect_answers, correct_answer }) =>

    [correct_answer, incorrect_answers].flat()

  );

  return (

    <>

      <Toggle

        setQuestionData={setQuestionData}

      />

    </>

  );

};

Toggle.js，点击开始按钮，通过axios访问远程接口，获得题目及答案。

import React from "react";

import axios from "axios";

import ToggleHeader from "./ToggleHeader";

import {

  Button,

  Form,

} from "reactstrap";

export const Toggle = ({

  setQuestionData,

}) => {

  const getData = async () => {

    try {

      const incomingData = await axios.get(

        `https://opentdb.com/api.php?amount=10&category=18&difficulty=easy&type=multiple`

      );

      setQuestionData(incomingData.data.results);

    } catch (err) {

      console.error(err);

    }

  };

  return (

    <>

      <ToggleHeader />

      <Form

        onSubmit={(e) => {

          e.preventDefault();

          getData();

        }}

      >

        <Button color="primary">开始</Button>

      </Form>

    </>

  );

};

ToggleHeader.js

import React from "react";

import { Jumbotron, Container} from "reactstrap";

export default function ToggleHeader() {

  return (

    <Jumbotron fluid>

      <Container fluid>

        <h1 className="display-4">计算机知识小测验</h1>

      </Container>

    </Jumbotron>

  );

}

https://opentdb.com/api.php接口返回的json数据格式为

{

	"response_code": 0,

	"results": [{

		"category": "Science: Computers",

		"type": "multiple",

		"difficulty": "easy",

		"question": "The numbering system with a radix of 16 is more commonly referred to as ",

		"correct_answer": "Hexidecimal",

		"incorrect_answers": ["Binary", "Duodecimal", "Octal"]

	}, {

		"category": "Science: Computers",

		"type": "multiple",

		"difficulty": "easy",

		"question": "This mobile OS held the largest market share in 2012.",

		"correct_answer": "iOS",

		"incorrect_answers": ["Android", "BlackBerry", "Symbian"]

	}, {

		"category": "Science: Computers",

		"type": "multiple",

		"difficulty": "easy",

		"question": "How many values can a single byte represent?",

		"correct_answer": "256",

		"incorrect_answers": ["8", "1", "1024"]

	}, {

		"category": "Science: Computers",

		"type": "multiple",

		"difficulty": "easy",

		"question": "In computing, what does MIDI stand for?",

		"correct_answer": "Musical Instrument Digital Interface",

		"incorrect_answers": ["Musical Interface of Digital Instruments", "Modular Interface of Digital Instruments", "Musical Instrument Data Interface"]

	}, {

		"category": "Science: Computers",

		"type": "multiple",

		"difficulty": "easy",

		"question": "In computing, what does LAN stand for?",

		"correct_answer": "Local Area Network",

		"incorrect_answers": ["Long Antenna Node", "Light Access Node", "Land Address Navigation"]

	}]

}

程序运行效果：

当前项目目录结构为：

2. 问题展示页面

Quiz.js，新增toggleView变量用来切换视图。

  const [toggleView, setToggleView] = useState(true);

Quiz.js，其中Question和QuestionHeader 组件，参见后面。

import { Question } from "./Question";

import { Jumbotron } from "reactstrap";

import QuestionHeader from "./QuestionHeader";

...

export const Quiz = () => {

  var [index, setIndex] = useState(0);

  const [questionData, setQuestionData] = useState([]);

...

 return (

    <>

      {toggleView && (

        <Toggle

          setIndex={setIndex}

          setQuestionData={setQuestionData}

          setToggleView={setToggleView}

        />

      )}

       {!toggleView &&

        (

          <Jumbotron>

            <QuestionHeader

              setToggleView={setToggleView}

            />

            <Question question={questions[index]} />

          </Jumbotron>

        )}

    </>

  );

使用index控制题目索引

var [index, setIndex] = useState(0);

修改Toggle.js

获取完远程数据，通过setToggleView(false);切换视图。

export const Toggle = ({

  setQuestionData,

  setToggleView,

  setIndex,

}) => {

...

  return (

    <>

      <ToggleHeader />

      <Form

        onSubmit={(e) => {

          e.preventDefault();

          getData();

          setToggleView(false);

          setIndex(0);

        }}

      >

        <Button color="primary">开始</Button>

      </Form>

    </>

  );

};

QuestionHeader.js代码：

同样的，点击返回首页按钮 setToggleView(true)，切换视图。

import React from "react";

import { Button } from "reactstrap";

export default function QuestionHeader({ setToggleView, category }) {

  return (

    <>

      <Button color="link" onClick={() => setToggleView(true)}>

        返回首页

      </Button>

    </>

  );

}

Question.js代码

接受父组件传过来的question对象，并显示。

其中he.decode是对字符串中的特殊字符进行转义。

import React from "react";

import he from "he";

export const Question = ({ question }) => {

  // he is a oddly named library that decodes html into string values

  var decode = he.decode(String(question));

  return (

    <div>

      <hr className="my-2" />

      <h1 className="display-5">

        {decode}

      </h1>

      <hr className="my-2" />

      <br />

    </div>

  );

};

程序运行效果：

首页

点击开始后，显示问题：

当前项目目录结构为：

3. 加载等待动画

新增LoadingSpin.js

import React from "react";

import { Spinner } from "reactstrap";

export default function LoadingSpin() {

  return (

    <>

      <Spinner type="grow" color="primary" />

      <Spinner type="grow" color="secondary" />

      <Spinner type="grow" color="success" />

      <Spinner type="grow" color="danger" />

    </>

  );

}

修改Quiz.js



import LoadingSpin from "./LoadingSpin";

export const Quiz = () => {

  const [isLoading, setLoading] = useState(false);

  return (

    <>

      {toggleView && (

        <Toggle

          ...

          setLoading={setLoading}

        />

      )}

      {!toggleView &&

        (isLoading ? (

          <LoadingSpin />

        ) :

        (

          ...

        ))}

    </>

  );

};

修改Toggle.js



export const Toggle = ({

...

  setLoading,

}) => {

  const getData = async () => {

    try {

      setLoading(true);

      const incomingData = await axios.get(

        `https://opentdb.com/api.php?amount=10&category=18&difficulty=easy&type=multiple`

      );

      setQuestionData(incomingData.data.results);

      setLoading(false);

    } catch (err) {

      console.error(err);

    }

  };

 ...

};

运行效果：

目前代码结构：

4. 实现下一题功能

新增Answer.js，用户点击下一题按钮，修改index，触发主界面刷新，显示下一题：

import React from "react";

import { Button } from "reactstrap";

export const Answer = ({ setIndex, index }) => {

  function answerResult() {

    setIndex(index + 1);

  }

  return (

    <Button className="ansButton" onClick={answerResult}>

      下一题

    </Button>

  );

};

修改Quiz.js，添加Answer组件：

import { Answer } from "./Answer";

...

 {!toggleView &&

        (isLoading ? (

          <LoadingSpin />

        ) :

        (

          <Jumbotron>

            ...

            <Answer

            setIndex={setIndex}

            index={index}

            />

          </Jumbotron>

        ))}

运行效果：

点击下一题：

5. 实现选项展示

新增AnswerList.js。

通过属性answers传进来的选项列表，需要被打乱顺序（shuffle ）

import React from "react";

import { Answer } from "./Answer";

export const AnswerList = ({ answers, index, setIndex }) => {

  if (answers) var correctAns = answers[0];

  const shuffle = (array) => {

    return array.sort(() => Math.random() - 0.5);

  };

  const arrayCheck = (arg) => {

    return Array.isArray(arg) ? arg : [];

  };

  return (

    <>

      {shuffle(arrayCheck(answers)).map((text,ind) => (

        <Answer

          text={text}

          correct={correctAns}

          setIndex={setIndex}

          index={index}

          key={ind}

        />

      ))}

    </>

  );

};

修改Answer.js

import React from "react";

import he from "he";

import { Button } from "reactstrap";

export const Answer = ({ text, correct, setIndex, index }) => {

  function answerResult() {

    setIndex(index + 1);

  }

  var decode = he.decode(String(text));

  return (

    <Button className="ansButton" onClick={answerResult}>

      {decode}

    </Button>

  );

};

修改Quiz.js

// import { Answer } from "./Answer";

import { AnswerList } from "./AnswerList";

export const Quiz = () => {

...

  return (

    <>

      ...

      {!toggleView &&

        (isLoading ? (

          <LoadingSpin />

        ) :

        (

        ...

            <AnswerList

              answers={answers[index]}

              index={index}

              setIndex={setIndex}

            />

          </Jumbotron>

        ))}

    </>

  );

};

运行效果：

项目结构：

6. 记录用户成绩

修改quiz.js，添加setResult，并传递给AnswerList



export const Quiz = () => {

  var [result, setResult] = useState(null);

...

  return (

    <>

    ...

      {!toggleView &&

        (isLoading ? (

          <LoadingSpin />

        ) :

        (

          <Jumbotron>

          ...

            <AnswerList

              answers={answers[index]}

              index={index}

              setIndex={setIndex}

              setResult={setResult}

            />

          </Jumbotron>

        ))}

    </>

  );

};

修改AnswerList.js，传递setResult

import React from "react";

import { Answer } from "./Answer";

export const AnswerList = ({ answers, index,setResult, setIndex }) => {

...

  return (

    <>

      {shuffle(arrayCheck(answers)).map((text,ind) => (

        <Answer

          text={text}

          correct={correctAns}

          setIndex={setIndex}

          setResult={setResult}

          index={index}

          key={ind}

        />

      ))}

    </>

  );

};

修改Answer.js，用户点击选项，回调setResult，通知Quiz组件，本次选择是对是错。

import React from "react";

import { Button } from "reactstrap";

import he from 'he'

export const Answer = ({ text, correct, setResult,setIndex, index }) => {

  function answerResult() {

    setIndex(index + 1);

    correct === text ? setResult(true) : setResult(false);

  }

  var decode = he.decode(String(text));

  return (

    <Button className="ansButton" onClick={answerResult}>

      {decode}

    </Button>

  );

};

修改Quiz.js，放一个隐藏的GameOver组件，每当index发生变化的时候，触发GameOver中的useEffect代码，累计用户答对题目的数目（setRight）



import GameOver from "./GameOver";

export const Quiz = () => {

  const [right, setRight] = useState(0);

  const [gameIsOver, setGameOver] = useState(false);

  return (

   <>

      {toggleView && (

        <Toggle

          setIndex={setIndex}

          setQuestionData={setQuestionData}

          setToggleView={setToggleView}

          setLoading={setLoading}

        />

      )}

      {!toggleView &&

        (isLoading ? (

          <LoadingSpin />

        ) :

          (

            <Jumbotron>

              <QuestionHeader

                setToggleView={setToggleView}

              />

              <Question question={questions[index]} />

              <AnswerList

                answers={answers[index]}

                index={index}

                setIndex={setIndex}

                setResult={setResult}

              />

            </Jumbotron>

      ))}

      <GameOver

        right={right}

        setRight={setRight}

        quizLength={questions.length}

        setGameOver={setGameOver}

        result={result}

        index={index}

      />

    </>

  );

};

新增GameOver.js组件，当index === quizLength && index时，setGameOver(true)设置游戏结束，显示用户得分。

import React, { useEffect } from "react";

export default function GameOver({

  right,

  setRight,

  setGameOver,

  index,

  quizLength,

  result,

}) {

  useEffect(() => {

    if (result === true) {

      setRight(right + 1);

    } 

    if (index === quizLength && index) {

      setGameOver(true);

    }

  }, [index]);

  return <div></div>;

}

7. 游戏结束，展示用户得分

新增ScoreBoard.js

import React from "react";

export const ScoreBoard = ({ finalScore, right }) => {

  // if index === 0 then right === 0 --> this way when index is reset in toggle so is right answers

  const scoreFormatted = score => {

    if (score === 1) {

      return 100;

    } else if (score === 0) {

      return 0;

    } else {

      return score.toFixed(2) * 100;

    }

  }

  return (

    <>

      <>

        <h1 className="display-4">Correct Answers: {right}</h1>

        <hr className="my-2" />

        <h1 className="display-4">

          Final Score: %{scoreFormatted(finalScore)}

        </h1>

        <hr className="my-2" />

      </>

      <p>谢谢使用 </p>

    </>

  );

};

ScoreHeader.js

import React from "react";

import { Button } from "reactstrap";

export default function ScoreHeader({ setGameOver, setToggleView }) {

  return (

    <Button

      color="link"

      onClick={() => {

        setGameOver(false);

        setToggleView(true);

      }}

    >

      返回首页

    </Button>

  );

}

修改Quiz.js，当gameIsOver 变量为true时，显示得分页面。

import { ScoreBoard } from "./ScoreBoard";

import ScoreHeader from "./ScoreHeader";

export const Quiz = () => {

...

  return (

    <>

      {!toggleView &&

        !gameIsOver &&

        (isLoading ? (

          <LoadingSpin />

        ) :

        (

          ...

          ))}

      {gameIsOver && (

        <Jumbotron>

          <ScoreHeader

            setToggleView={setToggleView}

            setGameOver={setGameOver}

          />

          <ScoreBoard right={right} finalScore={right / index} />

        </Jumbotron>

      )}

   ...

    </>

  );

};

最后