vuecli中validate无法解析

提示框不能显示出来

源代码

<template>
<div>
  <el-form rel="loginForm" :model="form" :rules="rules" label-width="80px" class="login-box">
    <h3 class="login-title">综测登录</h3>
    <el-form-item label="账号" prop="username">
      <el-input type="text" placeholder="请输入账号" v-model="form.username"/>
    </el-form-item>
    <el-form-item label="密码" prop="password">
      <el-input type="password" placeholder="请输入密码" v-model="form.password"/>
    </el-form-item>
    <el-form-item class="button">
      <el-button type="primary" v-on:click="onSubmit('loginForm')">登录</el-button>
    </el-form-item>
  </el-form>

  <el-dialog title="温馨提示" :visible.sync="dialogVisible" width="30%"   :before-close="handleClose">
    <span>请输入账号和密码</span>
    <span slot="footer" class="dialog-footer">
      <el-button type="primary" @click="dialogVisible = false">确定</el-button>
    </span>
  </el-dialog>
</div>
</template>

<script>
export default {
  name: "longin",
  data(){
    return{
      form:{
          username:'',
          password:''
      },
      //表单验证，需要在el-from-item 元素中加prop属性
      rules:{
        username:[
          {required:true,message:'账号不可为空',trigger:'blur'}
        ],
        password:[
          {required:true,message:'密码不可为空',trigger:'blur'}
        ]
      },
      //对话框显示和隐藏
      dialogVisible:false
    }
  },
  methods: {
    onSubmit(formName){
    //  为表单绑定验证功能
      this.$refs[formName].validate((valid) => {
        if(valid){
        //  使用Vue-router 路由到指定页面，该方式称之为编程式导航
          this.$router.push("/Main");
        }
        else{
          this.dialogVisible = true;
          return false;
        }
      });
    }
  }
}
</script>

<style lang="scss" scoped>
.login-box{
  border: 1px solid #DCDFE6;
  width:400px;
  margin: 180px auto;
  padding: 35px 35px 15px 35px;
  border-radius: 5px;
  -webkit-border-radius: 5px;
  -moz-border-radius: 5px;
  box-shadow: 0 0 25px #909399;
}

.login-title{
  text-align: center;
  margin: 0 auto 40px auto;
  color: #303133
}

</style>

打印一下this.$refs[formName] 看看 。应该是 表单 验证写错了吧 。
ref="loginForm" 你写成rel了

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