NotifyDataSetChanged方法不会刷新我的RecyclerViewKotlin

我正在尝试理解为什么适配器方法notifyDataSetChanged（）无法刷新我的recyclerview。我在适配器这样的创建方法时找到了解决方案：

 fun setData(list: List){
    resumeList = list
    notifyDataSetChanged()
 }

此解决方案有效，但是，我想知道为什么我不能做这样的事情：

private lateinit var downloadAdapter: DownloadRecyclerAdapter

private fun setupAdapter() {
    downloadAdapter = DownloadRecyclerAdapter(
        this@DownloadActivity,
        downloadList,
        { id -> onViewClick(id) },
        { id -> onEditClick(id) },
        { id, position -> onDeleteClick(id, position) }
    )

    savedResumeRv.apply {
        layoutManager = LinearLayoutManager(context)
        layoutAnimation = AnimationUtils.loadLayoutAnimation(
            this@DownloadActivity,
            R.anim.layout_animation_down_to_up
        )
        adapter = downloadAdapter

    }
}

private fun observers() {
    downloadViewModel.getDownloadList().observe(this, Observer { list ->
        downloadList = list
        list?.let {
            downloadAdapter.notifyDataSetChanged()
            }
        })
}

downloadAdapter持有列表downloadList的相同实例，我不知道为什么当我在活动中通知适配器时无法正常工作。

 downloadList = list

由于这一行，不再是下载列表的参考

尝试

private fun observers() {
    downloadViewModel.getDownloadList().observe(this, Observer { list ->
      with(downloadList){
    clear()
    addAll(list)
}
        downloadList?.let {
            downloadAdapter.notifyDataSetChanged()
            }
        })
}