element ui的Upload 如何在关闭弹窗的时候清空图片

可以在关闭弹窗的时候，调用 element ui 的 Upload 组件的清空文件方法，示例代码如下：

<template>
  <el-dialog :visible.sync="dialogVisible" @before-close="handleBeforeClose">
    <el-upload
      ref="upload"
      action="/upload"
      :file-list="fileList"
      :on-change="handleChange"
      :on-success="handleSuccess"
    >
      <el-button slot="trigger">选择文件</el-button>
      <el-button slot="tip" type="primary">或者拖拽文件到此处上传</el-button>
    </el-upload>
  </el-dialog>
</template>

<script>
export default {
  data() {
    return {
      dialogVisible: false,
      fileList: []
    };
  },
  methods: {
    handleBeforeClose(done) {
      this.$refs.upload.clearFiles();
      done();
    },
    handleChange(file, fileList) {
      console.log(file, fileList);
      this.fileList = fileList;
    },
    handleSuccess(response, file, fileList) {
      console.log(response, file, fileList);
      this.fileList = fileList;
    }
  }
};
</script>

在弹窗即将关闭的时候，调用 Upload 组件的 clearFiles 方法，清空已选文件列表即可。