可以通过监听HttpEventType.UploadProgress事件来获取上传进度，并通过计算文件大小和上传进度的比例来更新页面上的进度条。示例代码如下：

import { HttpClient, HttpEventType } from '@angular/common/http';
import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class UploadService {

  constructor(private http: HttpClient) { }

  uploadFile(file: File) {
    const formData = new FormData();
    formData.append('file', file);

    return this.http.post('/api/upload', formData, {
      reportProgress: true,
      observe: 'events'
    }).subscribe(event => {
      if (event.type === HttpEventType.UploadProgress) {
        // 计算上传进度的百分比
        const percentDone = Math.round(100 * event.loaded / event.total);

        // 更新页面上的进度条
        // ...
      } else if (event.type === HttpEventType.Response) {
        console.log(event.body);
      }
    });
  }
}