与上一篇Vue中TodoList案例_删除有俩个文件变化了

App.vue：向儿子组件MyFooter传递参数todos

<template>
  <div id="root">
    <div class="todo-container">
      <div class="todo-wrap">
        <MyHeader :addTodo="addTodo"/>
        <MyList :todos="todos" :checkTodo="checkTodo" :deleteTodo="deleteTodo"/>
        <MyFooter :todos="todos"/>
      </div>
    </div>
  </div>

</template>

<script>
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{
      todos:[
        {id:'001',title:'唱',done:true},
        {id:'002',title:'跳',done:false},
        {id:'003',title:'rap',done:true},
        {id:'004',title:'篮球',done:true}
      ]
    }
  },
  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
        })
    },
    //删除一个todo
    deleteTodo(id){
        this.todos = this.todos.filter((todo)=>{
            return todo.id !==id
        })
    }
  }
}
</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-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>

MyFooter.vue：用props接收todos参数，全部{{todo.lengh}}获取长度，已完成利用reduce函数统计完成个数（原理，pre初始值0，循环加todo.done满足条件+1）

<template>
  <div class="todo-footer">
    <label>
      <input type="checkbox"/>
    </label>
    <span>
           <span>已完成{{doneTotal}}</span> / 全部{{todos.length}}
       </span>
    <button class="btn btn-danger">清除已完成的任务</button>
  </div>
</template>

<script>
export default {
  name: "MyFooter",
  props:[
      'todos'
  ],
  computed:{
    doneTotal(){
     /* const x = this.todos.reduce((pre,current)=>{
          console.log('@',pre,current)
          return pre+(current.done?1:0)
      },0)*/
      return  this.todos.reduce((pre,todo)=>pre+(todo.done?1:0),0)
    }
  }
}
</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>

效果：底部已完成/全部