vant中如何修改用户的头像

<style lang="less" scoped>
.EditUserINfo {
  .avatar {
    width: 30px;
    height: 30px;
  }
  /* 样式穿透 */ 
  /deep/ .van-image-preview__cover{
    /* 取消样式设置 */
    top: unset;
    left: 0;
    right: 0;
    bottom: 0;
    .van-nav-bar{
      background: #000;
    }
  }
}
</style>

<template>
  <div class="EditUserINfo">
    <van-nav-bar title="编辑资料" left-arrow @click-left="$router.back()"></van-nav-bar>
    <van-cell-group>
      <van-cell title="头像" is-link @click="onAvatarClick">
        <van-image class="avatar" round :src="user.photo" />
      </van-cell>
      <!-- 表单元素的hidden属性：隐藏表单元素 -->
      <input type="file" hidden ref="file" @change="onFileChange" />
      <van-cell title="昵称" is-link :value="user.name"></van-cell>
      <van-cell title="介绍" is-link value="内容"></van-cell>
      <van-cell title="性别" is-link :value="user.gender===0?'男':'女'"></van-cell>
      <van-cell title="生日" is-link :value="user.birthday"></van-cell>
    </van-cell-group>
    <!-- 头像预览,预览关闭文件重置 -->
    <van-image-preview v-model="isPreviewShow" :images="images" @close="$refs.file.value=''">
      <!-- 插入插槽cover -->
      <van-nav-bar
        slot="cover"
        left-text="取消"
        right-text="确定"
        @click-left="isPreviewShow=false"
        @click-right="onUpdateAvatar"
      />
    </van-image-preview>
  </div>
</template>
 
<script>
export default {
  name: "EditUserINfo",
  components: {},
  props: {},
  data() {
    return {
      user: {
        photo: "https://img.yzcdn.cn/vant/cat.jpeg",
        name: "凯文",
        gender: "男",
        birthday: "1996-12-18"
      }, //用户信息
      isPreviewShow: false,
      images: [] //预览图片列表
    };
  },
  watch: {},
  computed: {
    file() {
      return this.$refs["file"];
    }
  },
  methods: {
    onAvatarClick() {
      this.file.click();
    },
    onFileChange() {
      // 1.拿到file类型input选择的文件对象
      const fileObj = this.file.files[0];
      // 2.使用window.URL.createObjectURL(file)得到文件数据
      const fileData = window.URL.createObjectURL(fileObj);
      // 3.将img.src = 第2步的结果
      this.images = [fileData];
      this.isPreviewShow = true;
    },
    onUpdateAvatar() {
      // 1.构造包含文件数据的表单对象
      // 注意：含有文件的服务务必要放到FormData中
      // 用代码来构造一个表单对象，主要目的是用来异步发送文件上传
      // 参数一：键
      // 参数二：值
      const fd = new FormData()
      fd.append('photo',this.file.files[0])
      this.$toast.loading({
        duration: 1000,
        message:'保存中',
        forbidClick:true
      })
      this.isPreviewShow =false
      //this.$toast.success('保存成功')
    }
  },
  created() {},
  mounted() {}
};
</script>