■Getters 我们可以理解为store仓库的一个计算属性,它的作用主要是用来派生出一些新的状态。比如我们要把state状态的数据进行一次映射或者筛选,再把这个结果重新计算并提供给组件使用。
Getter的基本使用
■在state中有一个数组保存的几个学生对象
//store\index.js
state: {
students:[
{id:'1',name:'xiu',age:20},
{id:'2',name:'fan',age:18},
{id:'3',name:'yuan',age:23},
{id:'4',name:'liu',age:22}
]
},
■我们需要过滤掉年龄小于20岁的学生
■用以前的方法可以在组件中通过计算属性来过滤
//Home.vue
computed:{
getStu(){
return this.$store.state.students.filter(stu => stu.age > 20);
}
}
■但如果多个组件都需要获取小于20岁的学生,通过计算属性的话会写几遍完全相同的代码,这是没有意义的
■所以我们要通过getters来处理,getters默认将state作为第一个参数
//store\index.js
getters:{
getStu:state =>{
return state.students.filter(stu => stu.age > 20);
}
},
//Home.vue
<template>
<div class="home">
<h1>this is a home page</h1>
<h2>{{$store.getters.getStu}}</h2>
</div>
</template>
//About.vue
<template>
<div class="about">
<h1>This is an about page</h1>
<h2>{{$store.getters.getStu}}</h2>
</div>
</template>
■getter 也可以接受其他 getter 作为第二个参数:
getters:{
getStu:state =>{
return state.students.filter(stu => stu.age > 20);
},
getNum:(state,getters) =>{
return getters.getStu.length;
}
Getter的传参
■我们可以让getter返回一个函数来给它传参
- 假如我们想要在store.getter.getStu时来决定获取年龄大于多少岁的学生
- 这时候需要一个参数给getter
- 我们可以让getter返回一个函数
- 这样我们在store.getter.getStu时获取的是一个函数
- 在函数中接受参数,并做处理
getters:{
getAge(state){
return function (age){
state.students.filter(stu => stu.age > age);
}
},
//箭头函数写法
getAge:state => (age) =>{
return state.students.filter(stu => stu.age > age);
},
}
//Home.vue
<template>
<div class="home">
<h1>this is a home page</h1>
//获取年龄大于18岁的学生
<h2>{{$store.getters.getAge(18)}}</h2>
</div>
</template>
其他vuex文章
Vuex概念和作用解析
vuex-mutation同步函数
vuex-getters的使用
vuex-actions异步函数
vuex-modules的使用
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