App.vue（App组件）

变更部分：添加样式.btn-edit。

<template>
  <div id="app">
    <div class="todo-container">
      <div class="todo-wrap">
        <Header/>
        <List/>
        <Footer/>
      </div>
    </div>
  </div>
</template>

<script>
import Header from './components/Header.vue';
import List from "./components/List.vue";
import Footer from "./components/Footer.vue";

export default {
  name: 'App',
  components: {
    Header,
    List,
    Footer
  }
}
</script>

<style>
  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-edit{
    color: #fff;
    background-color: orange;
    border: 1px solid darkorange;
    margin-right: 5px;
  }

  .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>

store/index.js

变更部分：添加mutation方法UPDATE_TODO。

import Vue from "vue";
import Vuex, { Store } from "vuex";

Vue.use(Vuex);

const state = {
    todos:[
        {id:"001",title:"吃饭",done:true},
        {id:"002",title:"睡觉",done:true},
        {id:"003",title:"打豆豆",done:false},
    ]
}

const getters = {
    total(state){
        return state.todos.length;
    },
    doneTotal(state){
        return state.todos.reduce((pre,todo) => { return pre + (todo.done ? 1 : 0)}, 0)
    },
    isAllChecked(state,getters){
        return  getters.total > 0  && getters.total === getters.doneTotal
    }
}

const actions = {}

const mutations = {
    ADD_TODO(state,todoObj){
        state.todos.unshift(todoObj);
    },
    CHECK_TODO(state,id){
        state.todos.forEach(todo => {
            if(todo.id === id) todo.done = !todo.done;
        })
    },
    DELETE_TODO(state,id){
        state.todos = state.todos.filter(todo => todo.id !== id);
    },
    UPDATE_TODO(state,{id,title}){
        state.todos.forEach(todo => {
            if(todo.id === id) todo.title = title;
        })
    },
    CHECK_ALL_TODO(state,done){
        state.todos.forEach(todo => todo.done = done);
    },
    CLEAR_ALL_TODO_DONE(state){
        state.todos = state.todos.filter(todo => !todo.done);
    }
}

export default new Store({
    state,
    getters,
    actions,
    mutations
})

Item.vue（Item组件）

主要变更部分：新增元素<input type="text"/>和<button>编辑</button>，新增方法handleBlur()和handleEdit()。

<template>
    <li>
        <label>
            <input type="checkbox" :checked="todo.done" @change="handleChange(todo.id)"/>
            <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="handleClick(todo.id)">删除</button>
        <button class="btn btn-edit" v-show="!todo.isEdit" @click="handleEdit(todo)">编辑</button>
    </li>
</template>

<script>
import {mapMutations} from "vuex";
export default {
    name:"Item",
    props:["todo"],
    methods:{
        ...mapMutations({
            handleChange:"CHECK_TODO"
        }),
        handleClick(id){
            if(confirm("确定删除吗？")){
                this.$store.commit("DELETE_TODO",id);
            }
        },
        handleEdit(todo){
            if(todo.hasOwnProperty("isEdit")){
                todo.isEdit = true;
            }else{
                this.$set(todo,"isEdit",true);
            }

            this.$nextTick(() => {
                this.$refs.inputTitle.focus();
            })
        },
        handleBlur(todo,event){
            if(!event.target.value.trim()) return alert("输入不能为空!");
            this.$store.commit("UPDATE_TODO",{id:todo.id,title:event.target.value});
            todo.isEdit = false;
        }
    }
}
</script>

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