我想把ListView改为RecyclerView。我想在RecyclerView中使用OnScrollListener的onScroll来确定用户是否滚动到列表的末尾。

我如何知道用户是否滚动到列表的末尾以便我可以从REST服务获取新数据?


当前回答

我有一个关于如何使用RecyclerView进行分页的非常详细的示例。在高层次,我有一个设置PAGE_SIZE,让我们说30。所以我请求30个项目,如果我得到30个,我就请求下一页。如果我得到的条目少于30个,我就标记一个变量来指示已经到达最后一页,然后停止请求更多的页面。看看吧,告诉我你的想法。

https://medium.com/@etiennelawlor/pagination-with-recyclerview-1cb7e66a502b

其他回答

我使用了recyclerview。adapter的onBindViewHolder方法。

适配器:

public interface OnViewHolderListener {
    void onRequestedLastItem();
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {

    ...

    if (position == getItemCount() - 1) onViewHolderListener.onRequestedLastItem();
}

片段(或活动):

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    contentView = inflater.inflate(R.layout.comments_list, container, false);
    recyclerView = (RecyclerView) mContentView.findViewById(R.id.my_recycler_view);
    adapter = new Adapter();
    recyclerView.setAdapter(adapter);

    ...

    adapter.setOnViewHolderListener(new Adapter.OnViewHolderListener() {
        @Override
        public void onRequestedLastItem() {
            //TODO fetch new data from webservice
        }
    });
    return contentView;
}

我在我的RecyclerView的onBindViewHolder方法中使用此逻辑实现了无限滚动类型。适配器类。

    if (position == mItems.size() - 1 && mCurrentPage <= mTotalPageCount) {
        if (mCurrentPage == mTotalPageCount) {
            mLoadImagesListener.noMorePages();
        } else {
            int newPage = mCurrentPage + 1;
            mLoadImagesListener.loadPage(newPage);
        }
    }

使用这段代码,当RecyclerView到达最后一项时,它会增加当前页面和接口上的回调,该接口负责从api加载更多数据并将新结果添加到适配器。

我可以张贴更完整的例子,如果这不是很清楚?

Create an abstract class and extends RecyclerView.OnScrollListener public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener { private int previousTotal = 0; private boolean loading = true; private int visibleThreshold; private int firstVisibleItem, visibleItemCount, totalItemCount; private RecyclerView.LayoutManager layoutManager; public EndlessRecyclerOnScrollListener(RecyclerView.LayoutManager layoutManager, int visibleThreshold) { this.layoutManager = layoutManager; this.visibleThreshold = visibleThreshold; } @Override public void onScrolled(RecyclerView recyclerView, int dx, int dy) { super.onScrolled(recyclerView, dx, dy); visibleItemCount = recyclerView.getChildCount(); totalItemCount = layoutManager.getItemCount(); firstVisibleItem = ((LinearLayoutManager)layoutManager).findFirstVisibleItemPosition(); if (loading) { if (totalItemCount > previousTotal) { loading = false; previousTotal = totalItemCount; } } if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) { onLoadMore(); loading = true; } } public abstract void onLoadMore();} in activity (or fragment) add addOnScrollListener to recyclerView LinearLayoutManager mLayoutManager = new LinearLayoutManager(this); recyclerView.setLayoutManager(mLayoutManager); recyclerView.addOnScrollListener(new EndlessRecyclerOnScrollListener(mLayoutManager, 3) { @Override public void onLoadMore() { //TODO ... } });

正如约翰·T所建议的。只需使用下面的代码块,真的很简短,美观简单:D

public void loadMoreOnRecyclerView() {
    mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrolled(@NonNull @NotNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            if (!recyclerView.canScrollVertically(1) && dy != 0) {
                //Load more items here
            }
        }
    });
}

你可以跟随我的回购来了解它的工作方式。

https://github.com/Nghien-Nghien/PokeAPI-Java/blob/0d8d69d348e068911b883f0ae7791d904cc75cb5/app/src/main/java/com/example/pokemonapi/MainActivity.java

关于应用程序的描述信息如下:https://github.com/skydoves/Pokedex#readme

借助Kotlin扩展函数的强大功能,代码可以看起来更加优雅。把它放在你想要的任何地方(我把它放在一个ExtensionFunctions中。kt文件):

/**
 * WARNING: This assumes the layout manager is a LinearLayoutManager
 */
fun RecyclerView.addOnScrolledToEnd(onScrolledToEnd: () -> Unit){

    this.addOnScrollListener(object: RecyclerView.OnScrollListener(){

        private val VISIBLE_THRESHOLD = 5

        private var loading = true
        private var previousTotal = 0

        override fun onScrollStateChanged(recyclerView: RecyclerView,
                                          newState: Int) {

            with(layoutManager as LinearLayoutManager){

                val visibleItemCount = childCount
                val totalItemCount = itemCount
                val firstVisibleItem = findFirstVisibleItemPosition()

                if (loading && totalItemCount > previousTotal){

                    loading = false
                    previousTotal = totalItemCount
                }

                if(!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)){

                    onScrolledToEnd()
                    loading = true
                }
            }
        }
    })
}

然后像这样使用它:

youRecyclerView.addOnScrolledToEnd {
    //What you want to do once the end is reached
}

这个解决方案基于Kushal Sharma的回答。然而,这是一个更好的,因为:

它使用onScrollStateChanged而不是onScroll。这样做比较好,因为每当RecyclerView中有任何类型的移动时,onScroll都会被调用,而onScrollStateChanged只在RecyclerView的状态改变时被调用。使用onScrollStateChanged将节省CPU时间,从而节省电池。 因为它使用扩展函数,所以可以在任何RecyclerView中使用。客户端代码只有一行。