我正在创建一个聊天应用程序，我正在尝试以相反的方式实现RecyclerView的无限滚动，例如从底部开始向上滚动，当达到顶部时，加载更多。
当用户打开聊天屏幕时，应用会收到最后20条消息并默认滚动到底部。我想在用户向上滚动时从服务器获取更多消息。
以下是我正在测试的通用无限滚动代码：
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
layoutManager = new LinearLayoutManager(this);
recyclerView = (RecyclerView)findViewById(R.id.recyclerview);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
adapter = new RecyclerViewAdapter<String, ItemViewHolder>(String.class,R.layout.item,ItemViewHolder.class,list) {
@Override
protected void populateViewHolder(ItemViewHolder viewHolder, String model, int position) {
if(model != null){
viewHolder.textView.setText(model);
}
}
};
recyclerView.setAdapter(adapter);
recyclerView.setOnScrollListener(new EndlessReverseRecyclerViewScrollListener(layoutManager) {
@Override
public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
loadMore();
}
});
loadInit();
}
private void loadInit(){
for(int x = 0; x < 20;x++){
list.add(list.size()+": "+getRandomString(8));
adapter.notifyDataSetChanged();
}
layoutManager.scrollToPosition(list.size() -1);
}
private void loadMore(){
for(int x = 0; x < 20;x++){
list.add(list.size()+": "+getRandomString(8));
adapter.notifyDataSetChanged();
}
}
无休止的滚动课
public EndlessReverseRecyclerViewScrollListener(LinearLayoutManager layoutManager) {
this.layoutManager = layoutManager;
}
// This happens many times a second during a scroll, so be wary of the code you place here.
// We are given a few useful parameters to help us work out if we need to load some more data,
// but first we check if we are waiting for the previous load to finish.
@Override
public void onScrolled(RecyclerView view, int dx, int dy) {
int lastVisibleItemPosition = 0;
int totalItemCount = layoutManager.getItemCount();
if (layoutManager instanceof StaggeredGridLayoutManager) {
int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) layoutManager).findLastVisibleItemPositions(null);
// get maximum element within the list
lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions);
} else if (layoutManager instanceof GridLayoutManager) {
lastVisibleItemPosition = ((GridLayoutManager) layoutManager).findLastVisibleItemPosition();
} else if (layoutManager instanceof LinearLayoutManager) {
lastVisibleItemPosition = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
}
Log.d(TAG," *** last visible: "+lastVisibleItemPosition);
Log.d(TAG," *** total: "+totalItemCount);
// If the total item count is zero and the previous isn't, assume the
// list is invalidated and should be reset back to initial state
if (totalItemCount < previousTotalItemCount) {
this.currentPage = this.startingPageIndex;
this.previousTotalItemCount = totalItemCount;
if (totalItemCount == 0) {
this.loading = true;
}
}
// If it’s still loading, we check to see if the dataset count has
// changed, if so we conclude it has finished loading and update the current page
// number and total item count.
if (loading && (totalItemCount > previousTotalItemCount)) {
loading = false;
previousTotalItemCount = totalItemCount;
}
// If it isn’t currently loading, we check to see if we have breached
// the visibleThreshold and need to reload more data.
// If we do need to reload some more data, we execute onLoadMore to fetch the data.
// threshold should reflect how many total columns there are too
if (!loading && (lastVisibleItemPosition + visibleThreshold) > totalItemCount) {
currentPage++;
onLoadMore(currentPage, totalItemCount, view);
loading = true;
}
}
// Call this method whenever performing new searches
public void resetState() {
this.currentPage = this.startingPageIndex;
this.previousTotalItemCount = 0;
this.loading = true;
}
// Defines the process for actually loading more data based on page
public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);
这适用于从上到下滚动，有人可以协助我如何使其从下到上工作。感谢
P.S。 ReverseLayout不是我正在寻找的解决方案，因为它只是颠倒了我的商品的顺序，而不是我想要实现的目标。
答案 0 :(得分：5)
我相信你正在寻找这种方法
LinearLayoutManager.setReverseLayout（真）
如果你不希望你的物品从底部堆叠另外设置
对于LinearLayoutManager ，setStackFromEnd（boolean）为false
答案 1 :(得分：2)
自从过去几天以来，我一直面临同样的担忧，这就是我提出的问题。 两个方向的无尽滚动监听器（顶部/底部）。
注意：我还没有对＃34; GridLayoutManager＆＃34;进行测试。
public abstract class EndlessRecyclerViewScrollListener extends RecyclerView.OnScrollListener {
// Sets the starting page index
private static final int startingPageIndex = 0;
// The minimum amount of items to have below your current scroll position
// before loading more.
private int visibleThreshold = 5;
// The current offset index of data you have loaded
private int currentPage = 0;
// The total number of items in the dataset after the last load
private int previousTotalItemCount = 0;
// True if we are still waiting for the last set of data to load.
private boolean loading = true;
private RecyclerView.LayoutManager mLayoutManager;
private LoadOnScrollDirection mDirection;
public EndlessRecyclerViewScrollListener(LinearLayoutManager layoutManager, LoadOnScrollDirection direction) {
this.mLayoutManager = layoutManager;
mDirection = direction;
}
public EndlessRecyclerViewScrollListener(GridLayoutManager layoutManager, LoadOnScrollDirection direction) {
this.mLayoutManager = layoutManager;
visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
mDirection = direction;
}
public EndlessRecyclerViewScrollListener(StaggeredGridLayoutManager layoutManager, LoadOnScrollDirection direction) {
this.mLayoutManager = layoutManager;
visibleThreshold = visibleThreshold * layoutManager.getSpanCount();
mDirection = direction;
}
// This happens many times a second during a scroll, so be wary of the code you place here.
// We are given a few useful parameters to help us work out if we need to load some more data,
// but first we check if we are waiting for the previous load to finish.
@Override
public void onScrolled(@NonNull RecyclerView view, int dx, int dy) {
int lastVisibleItemPosition = 0;
int firstVisibleItemPosition = 0;
int totalItemCount = mLayoutManager.getItemCount();
if (mLayoutManager instanceof StaggeredGridLayoutManager) {
int[] lastVisibleItemPositions =
((StaggeredGridLayoutManager) mLayoutManager).findLastVisibleItemPositions(null);
int[] firstVisibleItemPositions =
((StaggeredGridLayoutManager) mLayoutManager).findFirstVisibleItemPositions(null);
// get maximum element within the list
lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions);
firstVisibleItemPosition = getFirstVisibleItem(firstVisibleItemPositions);
} else if (mLayoutManager instanceof LinearLayoutManager) {
lastVisibleItemPosition =
((LinearLayoutManager) mLayoutManager).findLastVisibleItemPosition();
firstVisibleItemPosition =
((LinearLayoutManager) mLayoutManager).findFirstVisibleItemPosition();
} else if (mLayoutManager instanceof GridLayoutManager) {
lastVisibleItemPosition = ((GridLayoutManager) mLayoutManager).findLastVisibleItemPosition();
firstVisibleItemPosition = ((GridLayoutManager) mLayoutManager).findFirstVisibleItemPosition();
}
switch (mDirection) {
case BOTTOM:
// If the total item count is zero and the previous isn't, assume the
// list is invalidated and should be reset back to initial state
if (totalItemCount < previousTotalItemCount) {
this.currentPage = startingPageIndex;
this.previousTotalItemCount = totalItemCount;
if (totalItemCount == 0) {
this.loading = true;
}
}
// If it’s still loading, we check to see if the dataset count has
// changed, if so we conclude it has finished loading and update the current page
// number and total item count.
if (loading && (totalItemCount > previousTotalItemCount)) {
loading = false;
previousTotalItemCount = totalItemCount;
}
// If it isn’t currently loading, we check to see if we have breached
// the visibleThreshold and need to reload more data.
// If we do need to reload some more data, we execute onLoadMore to fetch the data.
// threshold should reflect how many total columns there are too
if (!loading && (lastVisibleItemPosition + visibleThreshold) > totalItemCount) {
currentPage++;
onLoadMore(currentPage, totalItemCount);
loading = true;
}
break;
case TOP:
// If the total item count is zero and the previous isn't, assume the
// list is invalidated and should be reset back to initial state
if (totalItemCount < previousTotalItemCount) {
this.currentPage = startingPageIndex;
this.previousTotalItemCount = totalItemCount;
if (totalItemCount == 0) {
this.loading = true;
}
}
// If it’s still loading, we check to see if the dataset count has
// changed, if so we conclude it has finished loading and update the current page
// number and total item count.
if (loading && (totalItemCount > previousTotalItemCount)) {
loading = false;
previousTotalItemCount = totalItemCount;
}
// If it isn’t currently loading, we check to see if we have breached
// the visibleThreshold and need to reload more data.
// If we do need to reload some more data, we execute onLoadMore to fetch the data.
// threshold should reflect how many total columns there are too
if (!loading && firstVisibleItemPosition < visibleThreshold) {
currentPage++;
onLoadMore(currentPage, totalItemCount);
loading = true;
}
break;
}
}
private int getLastVisibleItem(int[] lastVisibleItemPositions) {
int maxSize = 0;
for (int i = 0; i < lastVisibleItemPositions.length; i++) {
if (i == 0) {
maxSize = lastVisibleItemPositions[i];
} else if (lastVisibleItemPositions[i] > maxSize) {
maxSize = lastVisibleItemPositions[i];
}
}
return maxSize;
}
private int getFirstVisibleItem(int[] firstVisibleItemPositions) {
int maxSize = 0;
for (int i = 0; i < firstVisibleItemPositions.length; i++) {
if (i == 0) {
maxSize = firstVisibleItemPositions[i];
} else if (firstVisibleItemPositions[i] > maxSize) {
maxSize = firstVisibleItemPositions[i];
}
}
return maxSize;
}
// Defines the process for actually loading more data based on page
public abstract void onLoadMore(int page, int totalItemsCount);
public enum LoadOnScrollDirection {
TOP, BOTTOM
}
}
实施
LinearLayoutManager layoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
layoutManager.setStackFromEnd(true);
mBinding.rvChats.setLayoutManager(layoutManager);
mBinding.rvChats.addOnScrollListener(new EndlessRecyclerViewScrollListener(layoutManager, EndlessRecyclerViewScrollListener.LoadOnScrollDirection.TOP) {
@Override
public void onLoadMore(int page, int totalItemsCount) {
mViewModel.fetchMessages(page);
}
});
答案 2 :(得分：0)
对于面临问题的新手，我的解决方案与已接受的答案相同，但是带有我的代码段，
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
linearLayoutManager.setReverseLayout(true);
chatRecyclerView.setLayoutManager(linearLayoutManager);
我使用了无尽而流畅的滚动。.pagination由android提供的库