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27. $nextTick ​

27.1 $nextTick ​

  • this.$nextTick(回调函数)
  • 作用：在下一次DOM更新结束后执行其指定的回调。
  • 什么时候用：当改变数据后，要基于更新后的心DOM进行某些操作时，要在nextTick所指定的回调函数中执行

所指定的回调，会在dom元素更新之后再执行

优化 TodoList ​

App.vue ​

vue
<template>
  <div id="root">
    <div class="todo-container">
      <div class="todo-wrap">
        <MyHeader @addTodo="addTodo" />
        <MyList :todos="todos" />
        <MyFooter :todos="todos" @checkAllTodo="checkAllTodo" @clearAllTodo="clearAllTodo" />
      </div>
    </div>
  </div>
</template>

<script>
import pubsub from 'pubsub-js'
import MyHeader from './components/MyHeader'
import MyList from './components/MyList'
import MyFooter from './components/MyFooter'

export default {
  name: 'App',
  components: { MyHeader, MyList, MyFooter },
  data() {
    return {
      //由于todos是MyHeader组件和MyFooter组件都在使用，所以放在App中（状态提升）
      todos: JSON.parse(localStorage.getItem('todos')) || []
    }
  },
  methods: {
    //添加一个todo
    addTodo(todoObj) {
      this.todos.unshift(todoObj)
    },
    //勾选or取消勾选一个todo
    checkTodo(id) {
      this.todos.forEach(todo => {
        if (todo.id === id) todo.done = !todo.done
      })
    },
    //更新一个todo
    updateTodo(id, title) {
      this.todos.forEach(todo => {
        if (todo.id === id) todo.title = title
      })
    },
    //删除一个todo
    deleteTodo(_, id) {
      this.todos = this.todos.filter(todo => todo.id !== id)
    },
    //全选or取消全选
    checkAllTodo(done) {
      this.todos.forEach(todo => {
        todo.done = done
      })
    },
    //清除所有已经完成的todo
    clearAllTodo() {
      this.todos = this.todos.filter(todo => {
        return !todo.done
      })
    }
  },
  watch: {
    todos: {
      deep: true,
      handler(value) {
        localStorage.setItem('todos', JSON.stringify(value))
      }
    }
  },
  mounted() {
    this.$bus.$on('checkTodo', this.checkTodo)
    this.$bus.$on('updateTodo', this.updateTodo)
    this.pubId = pubsub.subscribe('deleteTodo', this.deleteTodo)
  },
  beforeDestroy() {
    this.$bus.$off('checkTodo')
    this.$bus.$off('updateTodo')
    pubsub.unsubscribe(this.pubId)
  }
}
</script>

<style>
/*base*/
body {
  background: #fff;
}
.btn {
  display: inline-block;
  padding: 4px 12px;
  margin-bottom: 0;
  font-size: 14px;
  line-height: 20px;
  text-align: center;
  vertical-align: middle;
  cursor: pointer;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.2), 0 1px 2px rgba(0, 0, 0, 0.05);
  border-radius: 4px;
}
.btn-danger {
  color: #fff;
  background-color: #da4f49;
  border: 1px solid #bd362f;
}
.btn-edit {
  color: #fff;
  background-color: skyblue;
  border: 1px solid rgb(103, 159, 180);
  margin-right: 5px;
}
.btn-danger:hover {
  color: #fff;
  background-color: #bd362f;
}
.btn:focus {
  outline: none;
}
.todo-container {
  width: 600px;
  margin: 0 auto;
}
.todo-container .todo-wrap {
  padding: 10px;
  border: 1px solid #ddd;
  border-radius: 5px;
}
</style>

MyList.vue ​

vue
<template>
  <ul class="todo-main">
    <MyItem v-for="todoObj in todos" :key="todoObj.id" :todo="todoObj" />
  </ul>
</template>

<script>
import MyItem from './MyItem'

export default {
  name: 'MyList',
  components: { MyItem },
  //声明接收App传递过来的数据
  props: ['todos']
}
</script>

<style scoped>
/*main*/
.todo-main {
  margin-left: 0px;
  border: 1px solid #ddd;
  border-radius: 2px;
  padding: 0px;
}

.todo-empty {
  height: 40px;
  line-height: 40px;
  border: 1px solid #ddd;
  border-radius: 2px;
  padding-left: 5px;
  margin-top: 10px;
}
</style>

MyItem.vue ​

vue
<template>
  <li>
    <label>
      <input type="checkbox" :checked="todo.done" @change="handleCheck(todo.id)" />
      <!-- 如下代码也能实现功能，但是不太推荐，因为有点违反原则，因为修改了props -->
      <!-- <input type="checkbox" v-model="todo.done"/> -->
      <span v-show="!todo.isEdit">{{todo.title}}</span>
      <input type="text" v-show="todo.isEdit" :value="todo.title" @blur="handleBlur(todo,$event)" ref="inputTitle">
    </label>
    <button class="btn btn-danger" @click="handleDelete(todo.id)">删除</button>
    <button v-show="!todo.isEdit" class="btn btn-edit" @click="handleEdit(todo)">编辑</button>
  </li>
</template>

<script>
import pubsub from 'pubsub-js'
export default {
  name: 'MyItem',
  //声明接收todo
  props: ['todo'],
  methods: {
    //勾选or取消勾选
    handleCheck(id) {
      //通知App组件将对应的todo对象的done值取反
      // this.checkTodo(id)
      this.$bus.$emit('checkTodo', id)
    },
    //删除
    handleDelete(id) {
      if (confirm('确定删除吗？')) {
        //通知App组件将对应的todo对象删除
        // this.deleteTodo(id)
        // this.$bus.$emit('deleteTodo',id)
        pubsub.publish('deleteTodo', id)
      }
    },
    //编辑
    handleEdit(todo) {
      if (todo.hasOwnProperty('isEdit')) {
        todo.isEdit = true
      } else {
        // console.log('@')
        this.$set(todo, 'isEdit', true)
      }
      // 💖💖💖
      this.$nextTick(function () {
        this.$refs.inputTitle.focus()
      })
    },
    //失去焦点回调（真正执行修改逻辑）
    handleBlur(todo, e) {
      todo.isEdit = false
      if (!e.target.value.trim()) return alert('输入不能为空！')
      this.$bus.$emit('updateTodo', todo.id, e.target.value)
    }
  }
}
</script>

<style scoped>
/*item*/
li {
  list-style: none;
  height: 36px;
  line-height: 36px;
  padding: 0 5px;
  border-bottom: 1px solid #ddd;
}

li label {
  float: left;
  cursor: pointer;
}

li label li input {
  vertical-align: middle;
  margin-right: 6px;
  position: relative;
  top: -1px;
}

li button {
  float: right;
  display: none;
  margin-top: 3px;
}

li:before {
  content: initial;
}

li:last-child {
  border-bottom: none;
}

li:hover {
  background-color: #ddd;
}

li:hover button {
  display: block;
}
</style>

MyHeader.vue ​

vue
<template>
  <div class="todo-header">
    <input type="text" placeholder="请输入你的任务名称，按回车键确认" v-model="title" @keyup.enter="add" />
  </div>
</template>

<script>
import { nanoid } from 'nanoid'
export default {
  name: 'MyHeader',
  data() {
    return {
      //收集用户输入的title
      title: ''
    }
  },
  methods: {
    add() {
      //校验数据
      if (!this.title.trim()) return alert('输入不能为空')
      //将用户的输入包装成一个todo对象
      const todoObj = { id: nanoid(), title: this.title, done: false }
      //通知App组件去添加一个todo对象
      this.$emit('addTodo', todoObj, 1, 2, 3)
      //清空输入
      this.title = ''
    }
  }
}
</script>

<style scoped>
/*header*/
.todo-header input {
  width: 560px;
  height: 28px;
  font-size: 14px;
  border: 1px solid #ccc;
  border-radius: 4px;
  padding: 4px 7px;
}

.todo-header input:focus {
  outline: none;
  border-color: rgba(82, 168, 236, 0.8);
  box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075), 0 0 8px rgba(82, 168, 236, 0.6);
}
</style>

MyFooter.vue ​

vue
<template>
  <div class="todo-footer" v-show="total">
    <label>
      <!-- <input type="checkbox" :checked="isAll" @change="checkAll"/> -->
      <input type="checkbox" v-model="isAll" />
    </label>
    <span>
      <span>已完成{{doneTotal}}</span> / 全部{{total}}
    </span>
    <button class="btn btn-danger" @click="clearAll">清除已完成任务</button>
  </div>
</template>

<script>
export default {
  name: 'MyFooter',
  props: ['todos'],
  computed: {
    //总数
    total() {
      return this.todos.length
    },
    //已完成数
    doneTotal() {
      //此处使用reduce方法做条件统计
      /* const x = this.todos.reduce((pre,current)=>{
					console.log('@',pre,current)
					return pre + (current.done ? 1 : 0)
				},0) */
      //简写
      return this.todos.reduce((pre, todo) => pre + (todo.done ? 1 : 0), 0)
    },
    //控制全选框
    isAll: {
      //全选框是否勾选
      get() {
        return this.doneTotal === this.total && this.total > 0
      },
      //isAll被修改时set被调用
      set(value) {
        // this.checkAllTodo(value)
        this.$emit('checkAllTodo', value)
      }
    }
  },
  methods: {
    /* checkAll(e){
				this.checkAllTodo(e.target.checked)
			} */
    //清空所有已完成
    clearAll() {
      // this.clearAllTodo()
      this.$emit('clearAllTodo')
    }
  }
}
</script>

<style scoped>
/*footer*/
.todo-footer {
  height: 40px;
  line-height: 40px;
  padding-left: 6px;
  margin-top: 5px;
}

.todo-footer label {
  display: inline-block;
  margin-right: 20px;
  cursor: pointer;
}

.todo-footer label input {
  position: relative;
  top: -1px;
  vertical-align: middle;
  margin-right: 5px;
}

.todo-footer button {
  float: right;
  margin-top: 5px;
}
</style>

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