图片上传回显问题点击可放大图片

 <el-form-item label="活动图片" prop="fileList">
    <cos-el-upload
      ref="upload"
      :action="uploadUrl"
      :headers="{Authorization:tokenId}"
      :on-change="uploadChange"
      :on-remove="uploadRemove"
      :on-preview="handlePictureCardPreview"    //点击放大图片功能
      ****list-type="picture-card"****
      :on-success="handleAvatarSuccess"
      :on-error="handleAvatarError"
      :before-upload="beforeUpload"
      accept=".jpg, .jpeg, .png, .gif, .bmp"
      :limit="1"
      :file-list="fileList"
    >
      <i class="el-icon-plus"></i>
    </cos-el-upload>
    <el-dialog :visible.sync="dialogVisible"  :append-to-body="true">  **去掉遮罩层**
      <img width="100%" :src="dialogImageUrl" alt />
    </el-dialog>
  </el-form-item>

 **handlePictureCardPreview(file) {
      this.dialogImageUrl = file.url;
      this.dialogVisible = true;
    },**