在顶部添加新项后，Recycler视图未滚动到顶部，因为尚未对列表适配器进行更改

Question

我在实时数据的开头获取了包含新项的新列表，然后使用其数据更新适配器

viewModel.myLiveData.observe { this, Observer { myList -> 
        adapter.submitList(myList) 
        recyclerView.scrollToPosition(0)
}

Answer 1

submitList它是在后台线程上工作的，所以总会存在无法解决延迟的竞争条件。幸运的是，RecyclerView.AdapterDataObserver当列表计算完成时，我们可以使用回调来通知：

yourRecyclerViewAdapter.registerAdapterDataObserver(object: RecyclerView.AdapterDataObserver() {
    override fun onChanged() {
        recycler_view_list.scrollToPosition(0)
    }
    override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
        recycler_view_list.scrollToPosition(0)
    }
    override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
        recycler_view_list.scrollToPosition(0)
    }
    override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
        recycler_view_list.scrollToPosition(0)
    }
    override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
        recycler_view_list.scrollToPosition(0)
    }
    override fun onItemRangeChanged(positionStart: Int, itemCount: Int, payload: Any?) {
        recycler_view_list.scrollToPosition(0)
    }
})

viewModel.myLiveData.observe { this, Observer { myList -> 
        adapter.submitList(myList) 
}

Answer 2

使用这种方式

viewModel.myLiveData.observe { this, Observer { myList -> 
    adapter.submitList(myList) // Assuming you are notifying adapter by notifydatasetchanged()
    recyclerView.post { recyclerView.scrollToPosition(0) }
}

这里post给 UI 线程一些时间来用新数据填充 Recycler，然后调用scrollToPosition.