使用a-upload上传图片，如果beforeUpload直接返回false，仍然会执行onChange，图片会继续上传。
这里是采用在beforeUpload函数中返回一个promise来解决的，这样如果返回false就不会再继续上传了。
官网说明:返回一个 Promise 对象，Promise 对象 reject 时则停止上传，resolve 时开始上传。

<div style="padding: 5px 0 0 5px; height: 10%;">
   <a-upload
     name="file"
     :showUploadList="false"
     :action="uploadAction"
     :data="getUploadParamResult"
     :multiple="false"
     :headers="headers"
     :beforeUpload="beforeUpload"
     @preview="handlePreview"
     @change="handleChangeResult"
   >
     <div v-if="panesResult.length < 4">
       <a-button :disabled="false"> <a-icon type="upload" /> 上传 </a-button>
     </div>
     <div v-else>
       <a-button :disabled="true"> <a-icon type="upload" /> 上传 </a-button>
     </div>
   </a-upload>
 </div>
 <a-tabs style="height: 70%;" hideAdd v-model="activeKeyResult" type="editable-card" @edit="onEdit">
   <a-tab-pane v-for="pane in panesResult" :tab="pane.title" :key="pane.key" :closable="pane.closable">
     <div class="img-div-style">
       <img :src="pane.imageUrl" preview>
     </div>
   </a-tab-pane>
 </a-tabs>

methods:{
	beforeUpload (file) {
      return new Promise((resolve, reject) => {
        var testmsg=/^image\/(jpeg|png|jpg)$/.test(file.type)
        const isLt2M = file.size / 1024 / 1024 <=2//图片大小不超过2MB
        if (!testmsg) {
          this.$message.error('上传图片格式不对!');
          return reject(false);
        }
        if(!isLt2M) {
          this.$message.error('上传图片大小不能超过 2M!');
          return reject(false);
        }
        return resolve(true)
      });
    },
    
      handleChangeResult(info) {
        if (info.file.status !== 'uploading') {
          console.log(info.file, info.fileList);
        }
        if (info.file.status === 'done') {
          this.$message.success(`${info.file.name} 上传成功`);
          this.imageUrl = info.file.response.result.fileName;
          this.addTabResult(true); //参数含义 true:表示手动添加tab false:表示读取数据库信息添加tab

        } else if (info.file.status === 'error') {
          this.$message.error(`${info.file.name} 上传失败.`);
        }
      },
      
      handlePreview (file) {
        this.previewImage = file.url || file.thumbUrl
        this.previewVisible = true
      },
    }，
    computed: {
      uploadAction:function () {
        return this.url.fileUpload;
      },
    },