从0开始，手把手教你用Vue.js开发一个答题App

项目演示

项目源码

配套讲解视频

教程说明

本教程适合对Vue基础知识有一点了解，但不懂得综合运用，还未曾使用Vue从头开发过一个小型App的读者。本教程不对所有的Vue知识点进行讲解，而是手把手一步步从0到1，做出一个完整的小项目。目前网上的教程不是只有零散的知识点讲解；就是抛出一个开源的大项目，初级读者下载下来后，运行起来都很费劲，更谈不上理解这个项目是如何一步步开发出来的了。本教程试图弥补这个空白。

1. 项目初始化

1.1使用 Vue CLI 创建项目

如果你还没有安装 VueCLI，请执行下面的命令安装或是升级：
npm install --global @vue/cli

在命令行中输入以下命令创建 Vue 项目：

vue create vue-quiz

Vue CLI v4.3.1
? Please pick a preset:
> default (babel, eslint)
  Manually select features

default：默认勾选 babel、eslint，回车之后直接进入装包

manually：自定义勾选特性配置，选择完毕之后，才会进入装包

选择第 1 种 default.

安装结束，命令提示你项目创建成功，按照命令行的提示在终端中分别输入：

# 进入你的项目目录
cd vue-quiz

# 启动开发服务
npm run serve

启动成功，命令行中输出项目的 http 访问地址。打开浏览器，输入其中任何一个地址进行访问

image-20200707121732592

如果能看到该页面，恭喜你，项目创建成功了。

1.2 初始目录结构

项目创建好以后，下面我们来了解一下初始目录结构：

image-20200707122944401

1.3 调整初始目录结构，实现游戏设置页面

默认生成的目录结构不满足我们的开发需求，所以需要做一些自定义改动。

这里主要处理下面的内容：

删除初始化的默认文件
新增调整我们需要的目录结构

删除默认示例文件：

src/components/HelloWorld.vue
src/assets/logo.png

修改package.json，添加项目依赖：

 "dependencies": {
    "axios": "^0.19.2",
    "bootstrap": "^4.4.1",
    "bootstrap-vue": "^2.5.0",
    "core-js": "^3.6.5",
    "vue": "^2.6.11",
    "vue-router": "^3.1.5"
  },
  "devDependencies": {
    "@vue/cli-plugin-babel": "~4.4.0",
    "@vue/cli-plugin-eslint": "~4.4.0",
    "@vue/cli-plugin-router": "~4.4.0",
    "@vue/cli-service": "~4.4.0",
    "babel-eslint": "^10.1.0",
    "eslint": "^6.7.2",
    "eslint-plugin-vue": "^6.2.2",
    "vue-template-compiler": "^2.6.11"
  },

然后运行yarn install,安装依赖。

修改项目入口文件main.js，引入bootstrap-vue。

import Vue from 'vue'
import App from './App.vue'
import router from './router'
import BootstrapVue from 'bootstrap-vue'
import 'bootstrap/dist/css/bootstrap.css'
import 'bootstrap-vue/dist/bootstrap-vue.css'

Vue.config.productionTip = false

Vue.use(BootstrapVue)

const state = { questions: [] }

new Vue({
  router,
  data: state,
  render: h => h(App)
}).$mount('#app')

定义一个state对象来共享答题数据（答题页面和结果页面共享）

const state = { questions: [] }

src目录下新增eventBus.js消息总线，用来在组件间传递消息，代码如下：

import Vue from 'vue'
const EventBus = new Vue()
export default EventBus

修改App.vue，css样式略，请参考源码。

<template>
  <div id="app" class="bg-light">
    <Navbar></Navbar>
    <b-alert :show="dismissCountdown" dismissible variant="danger" @dismissed="dismissCountdown = 0">
      {{ errorMessage }}
    </b-alert>
    <div class="d-flex justify-content-center">
      <b-card no-body id="main-card" class="col-sm-12 col-lg-4 px-0">
        <router-view></router-view>
      </b-card>
    </div>
  </div>
</template>

<script>
import EventBus from './eventBus'
import Navbar from './components/Navbar'

export default {
  name: 'app',
  components: {
    Navbar
  },
  data() {
    return {
      errorMessage: '',
      dismissSecs: 5,
      dismissCountdown: 0
    }
  },
  methods: {
    showAlert(error) {
      this.errorMessage = error
      this.dismissCountdown = this.dismissSecs
    }
  },
  mounted() {
    EventBus.$on('alert-error', (error) => {
      this.showAlert(error)
    })
  },
  beforeDestroy() {
    EventBus.$off('alert-error')
  }
}
</script>

新增components/Navbar.vue，定义导航部分。

image-20200707125506858

<template>
    <b-navbar id="navbar" class="custom-info" type="dark" sticky>
      <b-navbar-brand id="nav-logo" :to="{ name: 'home' }">Vue-Quiz</b-navbar-brand>

      <b-navbar-nav class="ml-auto">
        <b-nav-item :to="{ name: 'home' }">New Game </b-nav-item>
        <b-nav-item href="#" target="_blank">About</b-nav-item>
      </b-navbar-nav>
    </b-navbar>
</template>

<script>
export default {
  name: 'Navbar'
}
</script>

<style scoped>

</style>

src目录下新增router/index.js，定义首页路由。

import Vue from 'vue'
import VueRouter from 'vue-router'
import MainMenu from '../views/MainMenu.vue'


Vue.use(VueRouter)

const routes = [
  {
    name: 'home',
    path: '/',
    component: MainMenu
  }
]

const router = new VueRouter({
  mode: 'history',
  base: process.env.BASE_URL,
  routes
})

export default router

src下新增views/MainMenu.vue，MainMenu主要包含GameForm组件。

<template>
<div>
  <b-card-header class="custom-info text-white font-weight-bold">New Game</b-card-header>
  <b-card-body class="h-100">
    <GameForm @form-submitted="handleFormSubmitted"></GameForm>
  </b-card-body>
</div>
</template>

<script>
import GameForm from '../components/GameForm'

export default {
  name: 'MainMenu',
  components: {
    GameForm
  },
  methods: {
    /** Triggered by custom 'form-submitted' event from GameForm child component. 
     * Parses formData, and route pushes to 'quiz' with formData as query
     * @public
     */
    handleFormSubmitted(formData) {
      const query = formData
      query.difficulty = query.difficulty.toLowerCase()
      this.$router.push({ name: 'quiz', query: query })
    }
  }
}
</script>

新增src/components/GameForm.vue，实现游戏初始设置。

image-20200707125814786

<template>
  <div>
    <LoadingIcon v-if="loading"></LoadingIcon>

    <div v-else>
      <b-form @submit="onSubmit">
        <b-form-group 
          id="input-group-number-of-questions"
          label="Select a number"
          label-for="input-number-of-questions"
          class="text-left"
        >
          <b-form-input
            id="input-number-of-questions"
            v-model="form.number"
            type="number"
            :min="minQuestions"
            :max="maxQuestions"
            required 
            :placeholder="`Between ${minQuestions} and ${maxQuestions}`"
          ></b-form-input>
        </b-form-group>

        <b-form-group id="input-group-category">
          <b-form-select
            id="input-category"
            v-model="form.category"
            :options="categories"
          ></b-form-select>
        </b-form-group>

        <b-form-group id="input-group-difficulty">
          <b-form-select
            id="input-difficulty"
            v-model="form.difficulty"
            :options="difficulties"
          ></b-form-select>
        </b-form-group>

        <b-form-group id="input-group-type">
          <b-form-select
            id="input-type"
            v-model="form.type"
            :options="types"
          ></b-form-select>
        </b-form-group>

        <b-button type="submit" class="custom-success">Submit</b-button>
      </b-form>
    </div>
  </div>
</template>

<script>
import LoadingIcon from './LoadingIcon'
import axios from 'axios'

export default {
  components: {
    LoadingIcon
  },
  data() {
    return {
      // Form data, tied to respective inputs
      form: {
        number: '',
        category: '',
        difficulty: '',
        type: ''
      },
      // Used for form dropdowns and number input
      categories: [{ text: 'Category', value: '' }],
      difficulties: [{ text: 'Difficulty', value: '' }, 'Easy', 'Medium', 'Hard'],
      types: [
        { text: 'Type', value: '' }, 
        { text: 'Multiple Choice', value: 'multiple' }, 
        { text: 'True or False', value: 'boolean'}
      ],
      minQuestions: 10,
      maxQuestions: 20,
      // Used for displaying ajax loading animation OR form
      loading: true
    }
  },
  created() {
    this.fetchCategories()
  },
  methods: {
    fetchCategories() {
      axios.get('https://opentdb.com/api_category.php')
      .then(resp => resp.data)
      .then(resp => {
        resp.trivia_categories.forEach(category => {
          this.categories.push({text: category.name, value: `${category.id}`})
        });
        this.loading = false;
      })
    },
    onSubmit(evt) {
      evt.preventDefault()
       /** Triggered on form submit. Passes form data
        * @event form-submitted
        * @type {number|string}
        * @property {object}
        */
      this.$emit('form-submitted', this.form)
    }
  }
}
</script>

GameForm组件，主要通过axios发起获取全部题目分类请求：

axios.get('https://opentdb.com/api_category.php')

新增src/components/LoadingIcon.vue，在异步请求数据未返回时，渲染等待图标。

<template>
  <div id="loading-icon" class="h-100 d-flex justify-content-center align-items-center">
    <img src="@/assets/ajax-loader.gif" alt="Loading Icon">
  </div>
</template>

<script>
export default {
  name: 'LoadingIcon'
}
</script>

新增src/assets/ajax-loader.gif等待动画文件，请参考项目源码。

1.4 运行项目

yarn run serve

image-20200707130702456

2. 答题页面开发

image-20200708083506391

2.1 修改路由

修改router/index.js：

import Vue from 'vue'
import VueRouter from 'vue-router'
import MainMenu from '../views/MainMenu.vue'
import GameController from '../views/GameController.vue'

Vue.use(VueRouter)

const routes = [
  {
    name: 'home',
    path: '/',
    component: MainMenu
  }, {
    name: 'quiz',
    path: '/quiz',
    component: GameController,
    props: (route) => ({ 
      number: route.query.number, 
      difficulty: route.query.difficulty, 
      category: route.query.category,
      type: route.query.type
    })
  }
]

const router = new VueRouter({
  mode: 'history',
  base: process.env.BASE_URL,
  routes
})

export default router

2.2 答题页面

新增views/GameController.vue

本页面是本项目最重要的模块，展示问题，和处理用户提交的答案，简单解析一下：

1.fetchQuestions函数通过请求远程接口获得问题列表。

2.setQuestions保存远程回应的问题列表到本地数组。

3.onAnswerSubmit处理用户提交的选项，调用nextQuestion函数返回下一问题。

<template>
  <div class="h-100">
    <LoadingIcon v-if="loading"></LoadingIcon>
    <Question :question="currentQuestion" @answer-submitted="onAnswerSubmit" v-else></Question>
  </div>
</template>

<script>
import EventBus from '../eventBus'
import ShuffleMixin from '../mixins/shuffleMixin'
import Question from '../components/Question'
import LoadingIcon from '../components/LoadingIcon'
import axios from 'axios'

export default {
  name: 'GameController',
  mixins: [ShuffleMixin],
  props: {
    /** Number of questions */
    number: {
      default: '10',
      type: String,
      required: true
    },
    /** Id of category. Empty string if not included in query */
    category: String,
    /** Difficulty of questions. Empty string if not included in query */
    difficulty: String,
    /** Type of questions. Empty string if not included in query */
    type: String
  },
  components: {
    Question,
    LoadingIcon
  },
  data() {
    return {
      // Array of custom question objects. See setQuestions() for format
      questions: [],
      currentQuestion: {},
      // Used for displaying ajax loading animation OR form
      loading: true
    }
  },
  created() {
    this.fetchQuestions()
  },
  methods: {
    /** Invoked on created()
     * Builds API URL from query string (props).
     * Fetches questions from API.
     * "Validates" return from API and either routes to MainMenu view, or invokes setQuestions(resp).
     * @public
     */
    fetchQuestions() {
      let url = `https://opentdb.com/api.php?amount=${this.number}`
      if (this.category)   url += `&category=${this.category}`
      if (this.difficulty) url += `&difficulty=${this.difficulty}`
      if (this.type)       url += `&type=${this.type}`

      axios.get(url)
        .then(resp => resp.data)
        .then(resp => {
          if (resp.response_code === 0) {
            this.setQuestions(resp)
          } else {
            EventBus.$emit('alert-error', 'Bad game settings. Try another combination.')
            this.$router.replace({ name: 'home' })
          }
        })
    },
    /** Takes return data from API call and transforms to required object setup. 
     * Stores return in $root.$data.state.
     * @public
     */
    setQuestions(resp) {
      resp.results.forEach(qst => {
        const answers = this.shuffleArray([qst.correct_answer, ...qst.incorrect_answers])
        const question = {
          questionData: qst,
          answers: answers,
          userAnswer: null,
          correct: null
        }
        this.questions.push(question)
      })
      this.$root.$data.state = this.questions
      this.currentQuestion = this.questions[0]
      this.loading = false
    },
    /** Called on submit.
     * Checks if answer is correct and sets the user answer.
     * Invokes nextQuestion().
     * @public
     */
    onAnswerSubmit(answer) {
      if (this.currentQuestion.questionData.correct_answer === answer) {
        this.currentQuestion.correct = true
      } else {
        this.currentQuestion.correct = false
      }
      this.currentQuestion.userAnswer = answer
      this.nextQuestion()
    },
    /** Filters all unanswered questions, 
     * checks if any questions are left unanswered, 
     * updates currentQuestion if so, 
     * or routes to "result" if not.
     * @public
     */
    nextQuestion() {
      const unansweredQuestions = this.questions.filter(q => !q.userAnswer)
      if (unansweredQuestions.length > 0) {
        this.currentQuestion = unansweredQuestions[0]
      } else {
        this.$router.replace({ name: 'result' })
      }
    }
  }
}
</script>

新增\src\mixins\shuffleMixin.js

打乱问题答案，因为远程返回的答案有规律。mixins是混入的意思，可以混入到我们的某个页面或组件中，补充页面或组件功能，便于复用。

const ShuffleMixin = {
    methods: {
      shuffleArray: (arr) => arr
        .map(a => [Math.random(), a])
        .sort((a, b) => a[0] - b[0])
        .map(a => a[1])
    }
  }

  export default ShuffleMixin

新增src/components/Question.vue

<template>
  <div>
    <QuestionBody :questionData="question.questionData"></QuestionBody>

    <b-card-body class="pt-0">
      <hr>
      <b-form @submit="onSubmit">
        <b-form-group
          label="Select an answer:"
          class="text-left"
        >
          <b-form-radio 
            v-for="(ans, index) of question.answers" 
            :key="index" 
            v-model="answer" 
            :value="ans"
          >
            <div v-html="ans"></div>
          </b-form-radio>
        </b-form-group>

        <b-button type="submit" class="custom-success">Submit</b-button>
      </b-form>
    </b-card-body>
  </div>
</template>

<script>
import QuestionBody from './QuestionBody'

export default {
  name: 'Question',
  props: {
    /** Question object containing questionData, possible answers, and user answer information. */
    question: {
      required: true,
      type: Object
    }
  },
  components: {
    QuestionBody
  },
  data() {
    return {
      answer: null
    }
  },
  methods: {
    onSubmit(evt) {
      evt.preventDefault()
      if (this.answer) {
        /** Triggered on form submit. Passes user answer.
        * @event answer-submitted
        * @type {number|string}
        * @property {string}
        */
        this.$emit('answer-submitted', this.answer)
        this.answer = null
      }
    } 
  }
}
</script>

新增src/components/QuestionBody.vue

image-20200708083544511

<template>
  <div>
    <b-card-header :class="variant" class="d-flex justify-content-between border-bottom-0">
      <div>{{ questionData.category }}</div>
      <div class="text-capitalize">{{ questionData.difficulty }}</div>
    </b-card-header>
    <b-card-body>
      <b-card-text class="font-weight-bold" v-html="questionData.question"></b-card-text>
    </b-card-body>
  </div>
</template>

<script>
export default {
  name: 'QuestionBody',
  props: {
    /** Object containing question data as given by API. */
    questionData: {
      required: true,
      type: Object
    }
  },
  data() {
    return {
      variants: { easy: 'custom-success', medium: 'custom-warning', hard: 'custom-danger', default: 'custom-info' },
      variant: 'custom-info'
    }
  },
  methods: {
    /** Invoked on mounted().
     * Sets background color of card header based on question difficulty.
     * @public
     */
    setVariant() {
      switch (this.questionData.difficulty) {
        case 'easy':
          this.variant = this.variants.easy
          break
        case 'medium':
          this.variant = this.variants.medium
          break
        case 'hard':
          this.variant = this.variants.hard
          break
        default:
          this.variant = this.variants.default
          break
      }
    }
  },
  mounted() {
    this.setVariant()
  }
}
</script>

<docs>
Simple component displaying question category, difficulty and question text. 
Used on both Question component and Answer component.
</docs>

运行：

yarn run serve

启动成功:

image-20200708083506391

如果能看到该页面，恭喜你，项目到此成功了。

2.3 至此项目目录结构

如果你走丢，请下载源码进行对比：

image-20200708084009828

3 实现最终结果展示页面

image-20200708084853745

再次修改router/index.js

import Vue from 'vue'
import VueRouter from 'vue-router'
import MainMenu from '../views/MainMenu.vue'
import GameController from '../views/GameController.vue'
import GameOver from '../views/GameOver'

Vue.use(VueRouter)

const routes = [
  ...
  {
    name: 'result',
    path: '/result',
    component: GameOver
  }
]

...

新增src/views/GameOver.vue：

<template>
  <div class="h-100">
      <b-card-header class="custom-info text-white font-weight-bold">Your Score: {{ score }} / {{ maxScore }}</b-card-header>
    <Answer v-for="(question, index) of questions" :key="index" :question="question"></Answer>
  </div>
</template>

<script>
import Answer from '../components/Answer'

export default {
  name: 'GameOver',
  components: {
    Answer
  },
  data() {
    return {
      questions: [],
      score: 0,
      maxScore: 0
    }
  },
  methods: {
    /** Invoked on created().
     * Grabs data from $root.$data.state.
     * Empties $root.$data.state => This is done to ensure data is cleared when starting a new game.
     * Invokes setScore().
     * @public
     */
    setQuestions() {
      this.questions = this.$root.$data.state || []
      this.$root.$data.state = []
      this.setScore()
    },
    /** Computes maximum possible score (amount of questions * 10)
     * Computes achieved score (amount of correct answers * 10)
     * @public
     */
    setScore() {
      this.maxScore = this.questions.length * 10
      this.score = this.questions.filter(q => q.correct).length * 10
    }
  },
  created() {
    this.setQuestions();
  }
}
</script>

新增src\components\Answer.vue

<template>
  <div>
    <b-card no-body class="answer-card rounded-0">
      <QuestionBody :questionData="question.questionData"></QuestionBody>
      <b-card-body class="pt-0 text-left">
        <hr class="mt-0">
        <b-card-text 
          class="px-2" 
          v-html="question.questionData.correct_answer"
        >
        </b-card-text>
        <b-card-text 
          class="px-2" 
          :class="{ 'custom-success': question.correct, 'custom-danger': !question.correct }"
          v-html="question.userAnswer"
        >
        </b-card-text>
      </b-card-body>
    </b-card>
  </div>
</template>

<script>
import QuestionBody from './QuestionBody'

export default {
  name: 'Answer',
  props: {
    /** Question object containing questionData, possible answers, and user answer information. */
    question: {
      required: true,
      type: Object
    }
  },
  components: {
    QuestionBody
  }
}
</script>

<style scoped>
.answer-card >>> .card-header {
  border-radius: 0;
}
</style>

3.1 运行项目

yarn run serve

image

3.2 项目结构

image-20200708085222248

项目总结

很感谢您和豆约翰走到了这里，至此我们一个小型的Vue项目，全部开发完毕，下一期，豆约翰会带大家见识一个中型的项目，咱们循序渐进，一起加油。

本系列文章首发于作者的微信公众号[豆约翰]，想尝鲜的朋友，请微信搜索关注。

有什么问题也可以加我微信[tiantiancode]一起讨论。

最后

为了将来还能找到我

image