关于java：当已经在底部并添加新项目时，将recyclerView保持在底部

Keep recyclerView at bottom when already at bottom and new item is added

我正在创建一个聊天应用程序。当列表中的当前最低项目在屏幕上可见时，我试图让所有新消息出现在聊天应用程序的底部，但当用户向上滚动时(如大多数聊天应用程序)则不会。截至目前，当屏幕上仍有未使用的空间时，我已经让它工作了，但是当 RecyclerView 有太多视图无法容纳时，它开始将新消息放置到屏幕底部。这是我创建 RecyclerView 的方法：

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private void initRecyclerView() {

mRecyclerView = findViewById(R.id.chatRecyclerView);
mAdapter = new ChatRecyclerViewAdapter(this, mMessages, mUsernames, mRoomID, mDatabaseReference);
mRecyclerView.setAdapter(mAdapter);
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
linearLayoutManager.setStackFromEnd(true);
RecyclerView.AdapterDataObserver observer = new RecyclerView.AdapterDataObserver() {
@Override
public void onChanged() {
super.onChanged();

if(linearLayoutManager.findLastVisibleItemPosition()==(mAdapter.getItemCount()-1)){
mRecyclerView.smoothScrollToPosition(mAdapter.getItemCount()-1);
}
}
};
mAdapter.registerAdapterDataObserver(observer);
mRecyclerView.setLayoutManager(linearLayoutManager);

我最终添加了一个检查以查看 RecyclerView 是否位于底部，并将该布尔值插入 AdapterDataObserver。我还犯了使用观察者的 onChanged 方法而不是 onItemRangeInserted 的错误，这显然是补充 RecyclerViewAdapter 中的 notifyItemInserted 所必需的。

这是我的 RecyclerView 的工作代码，如果用户位于底部，它会自动将新消息放置在底部：

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private void initRecyclerView() {

//initializes and sets adapter

mRecyclerView = findViewById(R.id.chatRecyclerView);
mAdapter = new ChatRecyclerViewAdapter(this, mMessages, mUsernames, mRoomID, mDatabaseReference);
mRecyclerView.setAdapter(mAdapter);

//Creates layout manager and makes it feed new RecyclerView views from the bottom

final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
linearLayoutManager.setStackFromEnd(true);

//Makes RecyclerView scroll to bottom when notifyItemInserted is called from adapter and RecyclerView is already at bottom

RecyclerView.AdapterDataObserver observer = new RecyclerView.AdapterDataObserver() {
@Override
public void onItemRangeInserted(int positionStart, int itemCount) {
super.onItemRangeInserted(positionStart, itemCount);

if (isAtBottom) {
mRecyclerView.smoothScrollToPosition(mAdapter.getItemCount() - 1);
}
}
};

//Adds logic to see if RecyclerView is at bottom or not

mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);

if (!recyclerView.canScrollVertically(1)) {
isAtBottom = true;
} else {
isAtBottom = false;
}
}
});

//Assigns observer to adapter and LayoutManager to RecyclerView

mAdapter.registerAdapterDataObserver(observer);
mRecyclerView.setLayoutManager(linearLayoutManager);

}

mRecyclerView.smoothScrollToPosition(mAdapter.getItemCount()-1); // 删除这一行。

并使用这个：

1	mAdapter.notifyItemRangeInserted(mAdapter.getItemCount(), list.size() - 1);