从0开始，手把手教你使用React开发答题App

2021-07-28 05:34:40

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从0开始，手把手教你使用React开发答题App

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。
从0开始，手把手教你使用React开发答题App

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。

从0开始，手把手教你使用React开发答题App

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。
从0开始，手把手教你使用React开发答题App

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：
从0开始，手把手教你使用React开发答题App
当前项目目录结构为：
从0开始，手把手教你使用React开发答题App

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
从0开始，手把手教你使用React开发答题App
点击开始后，显示问题：
从0开始，手把手教你使用React开发答题App

当前项目目录结构为：
从0开始，手把手教你使用React开发答题App

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：
从0开始，手把手教你使用React开发答题App
目前代码结构：
从0开始，手把手教你使用React开发答题App

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：
从0开始，手把手教你使用React开发答题App
点击下一题：
从0开始，手把手教你使用React开发答题App

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：
从0开始，手把手教你使用React开发答题App
项目结构：
从0开始，手把手教你使用React开发答题App

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>
      )}
      
   ...
    </>
  );
};

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