<template>
  <Form ref="formValidate" :model="formValidate" :rules="ruleValidate">
    <FormItem prop="province" label="省份">
       <Select v-model="formValidate.province" placeholder="請選擇城市" @on-change="change">
        <Option v-for="item in provinceArr" :key="item.id" :value="item.id" >{{ item.name}}</Option>
       </Select>
    </FormItem>
    <FormItem prop="city" label="城市">
       <Select v-model="formValidate.city" placeholder="請選擇省份">
         <Option v-for="item in cities" :key="item.id" :value="item.id" >{{ item.name}}</Option>
       </Select>
     </FormItem>
   </Form>
</template>  

<script>
  export default{
    data(){
      return {
        provinceArr: [
          {
            id:1,
            name:"北京市",
            cities:[{id:11,
                name:"北京市"}]
          },
          {
            id:2,
            name:"天津市",
            cities:[{id:12,
                name:"天津市"} ]
          },
          {
            id:3,
            name:"上海市",
            cities:[ {id:13,
                name:"上海市"} ]
          }
        ],
        cities: "",
        formValidate:...,
        ruleValidate:...
      }
    },
    methods:{
      change(val){
       for(var i=0; i<this.provinceArr.length; i++){
        if(val == this.provinceArr[i].id ){
         this.cities = this.provinceArr[i].cities;
        }
       }
      }
    }
  }
</script>