Question

我正在创建一个聊天应用程序。我试图使所有新消息都显示在屏幕上可见列表中当前最低的项目时，而不是当用户向上滚动时（如大多数聊天应用程序），出现在聊天应用程序的底部。截至目前，当屏幕上仍然有未使用的空间时，我已经可以使用此功能，但是当RecyclerView的视图太多而无法容纳时，它将开始在屏幕底部显示新消息。这是我创建RecyclerView的方法：

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);

Answer 1

我最终添加了一个检查以查看RecyclerView是否在底部，并将该布尔值插入AdapterDataObserver。我还犯了一个错误，即使用观察者的onChanged方法而不是onItemRangeInserted，这显然是对RecyclerViewAdapter中的notifyItemInserted的补充。

这是我的RecyclerView的工作代码，如果用户位于底部，它将自动在底部放置新消息：

 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);
            } else {
            }
        }
    };

    //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);

}

Answer 2

mRecyclerView.smoothScrollToPosition(mAdapter.getItemCount()-1); //删除此行。

并使用它：

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

当recyclerView已在底部并添加新项时，将其保留在底部

2 个答案: