如何使用ng2-fileupload

Question

我正在尝试使用ng2-file-upload从多个文件的列表中上传单个文件。但是，只有我尝试上传的第一个文件才被实际上传。我该如何解决这个问题？谢谢。

singleUpload(fileName, item) {
  this.http.post('http://localhost:8080/api/profile/uploadDocument', {
    photo_image: fileName,
    user_id: this.userid

  }).subscribe(res => {
    console.log(fileName);
    this.uploader.uploadItem(item); // it only uploads file to sever once

    popupS.alert({
      title: 'Feedback',
      content: '<br><hr><div align="center">' + fileName + ' has been <br> 
      Uploaded < /div><hr><br>'
    });
  });
}