【Vue3】自定义指令

除了 Vue 内置的一系列指令 (比如 v-model 或 v-show) 之外，Vue 还允许你注册自定义的指令 (Custom Directives)。

1. 生命周期钩子函数

一个自定义指令由一个包含类似组件生命周期钩子的对象来定义。钩子函数会接收到指令所绑定元素作为其参数。

在 <script setup> 中，任何以 v 开头的驼峰式命名的变量都可以被用作一个自定义指令。

html 复制代码

<!-- App.vue -->
<template>
  <div>
    <button>切换</button>
    <!-- 
      钩子函数里面都可以接受这些值
      myParam: 自定义参数；
      myModifier: 自定义修饰符 
    -->
    <A v-move:myParam.myModifier="{ background: 'pink' }"></A>
  </div>
</template>

<script setup lang="ts">
import { reactive, ref, Directive } from 'vue';
import A from './components/A.vue';
import B from './components/B.vue';
let flag = ref<boolean>(true)
const vMove: Directive = {
  created() {
    console.log('created')
  },
  beforeMount() {
    console.log('beforeMount')
  },
  mounted(...args: Array<any>) {
    console.log('mounted')
    console.log(args);

  },
  beforeUpdate() {
    console.log('beforeUpdate')
  },
  updated() {
    console.log('updated')
  },
  beforeUnmount() {
    console.log('beforeUnmount')
  },
  unmounted() {
    console.log('unmounted')
  }
}
</script>

<style scoped lang="less"></style>

0：该 div 元素。
1：传入的参数等。比如 arg 参数，modifiers 自定义修饰符，dir 目录，传入的 value 值，instance 组件实例。
2：当前组件的虚拟 DOM
3：上一个虚拟 DOM

html 复制代码

<!-- App.vue -->
<template>
  <div>
    <button>切换</button>
    <!-- 
      钩子函数里面都可以接受这些值
      myParam: 自定义参数；
      myModifier: 自定义修饰符 
    -->
    <A v-move:myParam.myModifier="{ background: 'pink' }"></A>
  </div>
</template>

<script setup lang="ts">
import { reactive, ref, Directive, DirectiveBinding } from 'vue';
import A from './components/A.vue';
import B from './components/B.vue';
let flag = ref<boolean>(true)
type Dir = {
  background: string;
}
const vMove: Directive = {
  created() {
    console.log('created')
  },
  beforeMount() {
    console.log('beforeMount')
  },
  mounted(el: HTMLElement, dir: DirectiveBinding<Dir>) {
    console.log('mounted')
    console.log(el);
    console.log(dir);
    el.style.background = dir.value.background;
  },
  // 传入的数据发生变化（比如此时的background）时触发 beforeUpdate 和 updated
  beforeUpdate() {
    console.log('beforeUpdate')
  },
  updated() {
    console.log('updated')
  },
  beforeUnmount() {
    console.log('beforeUnmount')
  },
  unmounted() {
    console.log('unmounted')
  }
}
</script>

<style scoped lang="less"></style>

2. 指令简写

html 复制代码

<!-- App.vue -->
<template>
  <div class="btns">
    <button v-has-show="123">创建</button>
    <button>编辑</button>
    <button>删除</button>
  </div>
</template>

<script setup lang="ts">
import { reactive, ref, DirectiveBinding } from 'vue';
import type { Directive } from 'vue'
const vHasShow: Directive = (el, binding) => {
  console.log(el, binding) ;
}
</script>

<style scoped lang="less">
.btns {
  button {
    margin: 10px;
  }
}
</style>

应用场景1：按钮鉴权

根据能否从 localStorage（或者后台返回）中获取数据，来判断是否显示某个按钮。

html 复制代码

<!-- App.vue -->
<template>
  <div class="btns">
    <button v-has-show="'shop:create'">创建</button>
    <button v-has-show="'shop:edit'">编辑</button>
    <button v-has-show="'shop:delete'">删除</button>
  </div>
</template>

<script setup lang="ts">
import { reactive, ref, DirectiveBinding } from 'vue';
import type { Directive } from 'vue'
localStorage.setItem('userId', 'xiuxiu')
// mock 后台返回的数据
const permissions = [
  'xiuxiu:shop:create',
  // 'xiuxiu:shop:edit',  // 后台没有相应数据，则不显示该对应的按钮
  'xiuxiu:shop:delete'
]
const userId = localStorage.getItem('userId') as string
const vHasShow: Directive = (el, binding) => {
  if(!permissions.includes(userId + ':' + binding.value)) {
    el.style.display = 'none'
  }
}
</script>

<style scoped lang="less">
.btns {
  button {
    margin: 10px;
  }
}
</style>

应用场景2：鼠标拖拽

拖拽粉色框移动大盒子。

html 复制代码

<!-- App.vue -->
<template>
  <div v-move class="box">
    <div class="header"></div>
    <div>内容</div>
  </div>
</template>

<script setup lang="ts">
import { Directive, DirectiveBinding } from 'vue';


const vMove:Directive<any,void> = (el:HTMLElement, binding:DirectiveBinding)=> {
  let moveElement:HTMLElement = el.firstElementChild as HTMLElement;
  console.log(moveElement);
  const mouseDown = (e:MouseEvent) => {
    // 记录原始位置
    // clientX 鼠标点击位置的X轴坐标
    // clientY 鼠标点击位置的Y轴坐标
    // offsetLeft 鼠标点击的子元素距离其父元素的左边的距离
    // offsetTop 鼠标点击的子元素距离其父元素的顶部的距离
    let X = e.clientX - el.offsetLeft;
    let Y = e.clientY - el.offsetTop;
    const move = (e:MouseEvent) => {
      console.log(e);
      el.style.left = e.clientX - X + 'px';
      el.style.top = e.clientY - Y + 'px';
    }
    document.addEventListener('mousemove', move);
    document.addEventListener('mouseup', () => {
      document.removeEventListener('mousemove', move);
    })
  }
  moveElement.addEventListener('mousedown', mouseDown);
}
</script>

<style scoped lang="less">
.box {
  position: fixed;
  height: 200px;
  width: 200px;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  border: 1px solid #000;
  .header {
    height: 50px;
    width: 100%;
    background: pink;
    border-bottom: #000 1px solid;
  }
}
</style>

应用场景3：懒加载

let imageList = import.meta.glob('./assets/images/*.*', { eager: true })

let imageList = import.meta.glob('./assets/images/*.*')

 // 判断图片是否在可视区
 const observer = new IntersectionObserver((e)=> {
   console.log(e[0]);
 })  
 // 监听元素
 observer.observe(el)

html 复制代码

<!-- App.vue -->
<template>
  <div>
    <div>
      <img v-lazy="item" width="400" height="500" v-for="item in arr" alt="">
    </div>
  </div>
</template>

<script setup lang="ts">
import { Directive, DirectiveBinding } from 'vue';

let imageList:Record<string,{default:string}> = import.meta.glob('./assets/images/*.*', { eager: true })
let arr = Object.values(imageList).map(item=>item.default)
console.log(arr);
let vLazy:Directive<HTMLImageElement,string> = async (el,binding)=> {
  const def = await import('./assets/pinia.svg')
  el.src = def.default
  // 判断图片是否在可视区
  const observer = new IntersectionObserver((e)=> {
    console.log(e[0],binding.value);
    if(e[0].intersectionRatio > 0) {
      setTimeout(()=> {
        el.src = binding.value
      },2000)
      observer.unobserve(el)
    }
  })  
  // 监听元素
  observer.observe(el)
}
</script>

<style scoped lang="less"></style>

进入可视区比例 > 0：
过 2s ，替换图片