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

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

其他回答

有一个方法public void setOnScrollListener (RecyclerView。OnScrollListener监听器)在https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html#setOnScrollListener%28android.support.v7.widget.RecyclerView.OnScrollListener%29。使用这个

编辑:

在onScrollListener中重写onScrollStateChanged方法并执行此操作

            boolean loadMore = firstVisibleItem + visibleItemCount >= totalItemCount;

            //loading is used to see if its already loading, you have to manually manipulate this boolean variable
            if (loadMore && !loading) {
                 //end of list reached
            }

我刚试了一下:

    final LinearLayoutManager rvLayoutManager = new LinearLayoutManager(this);
    rvMovieList = (RecyclerView) findViewById(R.id.rvMovieList);
    rvMovieList.setLayoutManager(rvLayoutManager);
    adapter = new MovieRecyclerAdapter(this, movies);
    rvMovieList.setAdapter(adapter);
    adapter.notifyDataSetChanged();

    rvMovieList.addOnScrollListener(new OnScrollListener() {
        boolean loading = true;
        int pastVisiblesItems, visibleItemCount, totalItemCount;
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);

            visibleItemCount = rvLayoutManager.getChildCount();
            totalItemCount = rvLayoutManager.getItemCount();
            pastVisiblesItems = rvLayoutManager.findFirstVisibleItemPosition();

            int lastitem = visibleItemCount + pastVisiblesItems;

            if ( lastitem == totalItemCount
                    && page < total_pages
                    && !keyword.equals("") ) {
                // hit bottom ..

                String strnext;
                if (page == total_pages - 1) {
                    int last = total_results - (page * 20);
                    strnext = String.format(getResources().getString(R.string.next), last);
                } else {
                    strnext = String.format(getResources().getString(R.string.next), 20);
                }
                btNext.setText(strnext);
                btNext.setVisibility(View.VISIBLE);
            } else {
                btNext.setVisibility(View.INVISIBLE);
            }

            if(pastVisiblesItems == 0 &&  page > 1){
                // hit top
                btPrev.setVisibility(View.VISIBLE);
            } else {
                btPrev.setVisibility(View.INVISIBLE);
            }
        }
    });

我搞不清楚在哪里加载真或假,所以我试图删除它,这段代码工作如我所料。

大多数答案是假设RecyclerView使用LinearLayoutManager,或GridLayoutManager,甚至StaggeredGridLayoutManager,或假设滚动是垂直或水平的,但没有人张贴一个完全通用的答案。

使用ViewHolder的适配器显然不是一个好的解决方案。一个适配器可能有超过1个RecyclerView在使用它。它“改编”了它们的内容。它应该是RecyclerView(它是一个负责当前显示给用户的类,而不是适配器,它只负责向RecyclerView提供内容),它必须通知您的系统需要更多的项(加载)。

下面是我的解决方案,只使用了RecyclerView (RecycerView. view)的抽象类。LayoutManager和RecycerView.Adapter):

/**
 * Listener to callback when the last item of the adpater is visible to the user.
 * It should then be the time to load more items.
 **/
public abstract class LastItemListener extends RecyclerView.OnScrollListener {

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
      super.onScrolled(recyclerView, dx, dy);

      // init
      RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
      RecyclerView.Adapter adapter = recyclerView.getAdapter();

      if (layoutManager.getChildCount() > 0) {
        // Calculations..
        int indexOfLastItemViewVisible = layoutManager.getChildCount() -1;
        View lastItemViewVisible = layoutManager.getChildAt(indexOfLastItemViewVisible);
        int adapterPosition = layoutManager.getPosition(lastItemViewVisible);
        boolean isLastItemVisible = (adapterPosition == adapter.getItemCount() -1);

        // check
        if (isLastItemVisible)
          onLastItemVisible(); // callback
     }
   }

   /**
    * Here you should load more items because user is seeing the last item of the list.
    * Advice: you should add a bollean value to the class
    * so that the method {@link #onLastItemVisible()} will be triggered only once
    * and not every time the user touch the screen ;)
    **/
   public abstract void onLastItemVisible();

}


// --- Exemple of use ---

myRecyclerView.setOnScrollListener(new LastItemListener() {
    public void onLastItemVisible() {
         // start to load more items here.
    }
}

这个解决方案对我来说非常有效。

//Listener    

public abstract class InfiniteScrollListener     extendsRecyclerView.OnScrollListener {

public static String TAG = InfiniteScrollListener.class.getSimpleName();
int firstVisibleItem, visibleItemCount, totalItemCount;
private int previousTotal = 0;
private boolean loading = true;
private int visibleThreshold = 1;
private int current_page = 1;

private LinearLayoutManager mLinearLayoutManager;

public InfiniteScrollListener(LinearLayoutManager linearLayoutManager) {
    this.mLinearLayoutManager = linearLayoutManager;
}

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    super.onScrolled(recyclerView, dx, dy);

    visibleItemCount = recyclerView.getChildCount();
    totalItemCount = mLinearLayoutManager.getItemCount();
    firstVisibleItem = mLinearLayoutManager.findFirstVisibleItemPosition();

    if (loading) {
        if (totalItemCount > previousTotal) {
            loading = false;
            previousTotal = totalItemCount;
        }
    }
    if (!loading && (totalItemCount - visibleItemCount - firstVisibleItem <= visibleThreshold)) {

        current_page++;

        onLoadMore(current_page);

        loading = true;
    }
}

public void resetState() {
    loading = true;
    previousTotal = 0;
    current_page = 1;
}

public abstract void onLoadMore(int current_page);
}

//Implementation into fragment 
 private InfiniteScrollListener scrollListener;

scrollListener = new InfiniteScrollListener(manager) {
        @Override
        public void onLoadMore(int current_page) {
            //Load data
        }
    };
    rv.setLayoutManager(manager);
    rv.addOnScrollListener(scrollListener);

这里我的解决方案使用AsyncListUtil,在网络上说: 注意,这个类使用一个线程来加载数据,所以它适合从二级存储(如磁盘)加载数据,但不适合从网络加载数据。 但是我使用odata来读取数据并工作良好。 我在示例中遗漏了数据实体和网络方法。 我只包括示例适配器。

public class AsyncPlatoAdapter extends RecyclerView.Adapter {

    private final AsyncPlatoListUtil mAsyncListUtil;
    private final MainActivity mActivity;
    private final RecyclerView mRecyclerView;
    private final String mFilter;
    private final String mOrderby;
    private final String mExpand;

    public AsyncPlatoAdapter(String filter, String orderby, String expand, RecyclerView recyclerView, MainActivity activity) {
        mFilter = filter;
        mOrderby = orderby;
        mExpand = expand;
        mRecyclerView = recyclerView;
        mActivity = activity;
        mAsyncListUtil = new AsyncPlatoListUtil();

    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).
                inflate(R.layout.plato_cardview, parent, false);

        // Create a ViewHolder to find and hold these view references, and
        // register OnClick with the view holder:
        return new PlatoViewHolderAsync(itemView, this);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        final Plato item = mAsyncListUtil.getItem(position);
        PlatoViewHolderAsync vh = (PlatoViewHolderAsync) holder;
        if (item != null) {
            Integer imagen_id = item.Imagen_Id.get();
            vh.getBinding().setVariable(BR.plato, item);
            vh.getBinding().executePendingBindings();
            vh.getImage().setVisibility(View.VISIBLE);
            vh.getProgress().setVisibility(View.GONE);
            String cacheName = null;
            String urlString = null;
            if (imagen_id != null) {
                cacheName = String.format("imagenes/imagen/%d", imagen_id);
                urlString = String.format("%s/menusapi/%s", MainActivity.ROOTPATH, cacheName);
            }
            ImageHelper.downloadBitmap(mActivity, vh.getImage(), vh.getProgress(), urlString, cacheName, position);
        } else {
            vh.getBinding().setVariable(BR.plato, item);
            vh.getBinding().executePendingBindings();
            //show progress while loading.
            vh.getImage().setVisibility(View.GONE);
            vh.getProgress().setVisibility(View.VISIBLE);
        }
    }

    @Override
    public int getItemCount() {
        return mAsyncListUtil.getItemCount();
    }

    public class AsyncPlatoListUtil extends AsyncListUtil<Plato> {
        /**
         * Creates an AsyncListUtil.
         */
        public AsyncPlatoListUtil() {
            super(Plato.class, //my data class
                    10, //page size
                    new DataCallback<Plato>() {
                        @Override
                        public int refreshData() {
                            //get count calling ../$count ... odata endpoint
                            return countPlatos(mFilter, mOrderby, mExpand, mActivity);
                        }

                        @Override
                        public void fillData(Plato[] data, int startPosition, int itemCount) {
                            //get items from odata endpoint using $skip and $top
                            Platos p = loadPlatos(mFilter, mOrderby, mExpand, startPosition, itemCount, mActivity);
                            for (int i = 0; i < Math.min(itemCount, p.value.size()); i++) {
                                data[i] = p.value.get(i);
                            }

                        }
                    }, new ViewCallback() {
                        @Override
                        public void getItemRangeInto(int[] outRange) {
                            //i use LinearLayoutManager in the RecyclerView
                            LinearLayoutManager layoutManager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
                            outRange[0] = layoutManager.findFirstVisibleItemPosition();
                            outRange[1] = layoutManager.findLastVisibleItemPosition();
                        }

                        @Override
                        public void onDataRefresh() {
                            mRecyclerView.getAdapter().notifyDataSetChanged();
                        }

                        @Override
                        public void onItemLoaded(int position) {
                            mRecyclerView.getAdapter().notifyItemChanged(position);
                        }
                    });
            mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    onRangeChanged();
                }
            });
        }
    }
}