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

if (layoutManager.findLastCompletelyVisibleItemPosition() == 
 recyclerAdapter.getItemCount() - 1) {
    //load more items.
 }

公平而简单。 这是可行的。

其他回答

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();
                }
            });
        }
    }
}

下面是一个简单实现无尽滚动RecyclerView的例子,使用一个从各种来源编译的简单库。

在build.gradle中添加这一行

implementation 'com.hereshem.lib:awesomelib:2.0.1'

在活动中创建RecyclerView布局

<com.hereshem.lib.recycler.MyRecyclerView
        android:id="@+id/recycler"
        app:layoutManager="LinearLayoutManager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

通过传递ViewHolder支持的类来创建一个ViewHolder

public static class EVHolder extends MyViewHolder<Events> {
    TextView date, title, summary;
    public EVHolder(View v) {
        super(v);
        date = v.findViewById(R.id.date);
        title = v.findViewById(R.id.title);
        summary = v.findViewById(R.id.summary);
    }
    @Override
    public void bindView(Events c) {
        date.setText(c.date);
        title.setText(c.title);
        summary.setText(c.summary);
    }
}

通过在适配器中传递项目、类和布局来创建项目列表变量和很少行的适配器

List<Events> items = new ArrayList<>();
MyRecyclerView recycler = findViewById(R.id.recycler);
RecyclerViewAdapter adapter = new RecyclerViewAdapter(this, items, EVHolder.class, R.layout.row_event);
recycler.setAdapter(adapter);

ClickListener和LoadMore Listener可以通过以下几行添加

recycler.setOnItemClickListener(new MyRecyclerView.OnItemClickListener() {
    @Override
    public void onItemClick(int position) {
        Toast.makeText(MainActivity.this, "Recycler Item Clicked " + position, Toast.LENGTH_SHORT).show();
    }
});

recycler.setOnLoadMoreListener(new MyRecyclerView.OnLoadMoreListener() {
    @Override
    public void onLoadMore() {
        loadData();
    }
});
loadData();

数据加载后必须调用此函数

recycler.loadComplete();

当不需要LoadMore时,可以通过调用LoadMore来隐藏布局

recycler.hideLoadMore();

更多的例子可以在这里找到

希望这对你有所帮助。

if (layoutManager.findLastCompletelyVisibleItemPosition() == 
 recyclerAdapter.getItemCount() - 1) {
    //load more items.
 }

公平而简单。 这是可行的。

也可以在没有滚动侦听器的情况下实现,只使用数据模型的纯逻辑。滚动视图需要按位置获取项目以及最大项目计数。模型可以具有后台逻辑,以块的形式获取所需的项,而不是一个一个地获取,并在后台线程中执行此操作,在数据准备就绪时通知视图。

这种方法允许获取队列优先选择最近请求的(所以当前可见)项而不是旧的(很可能已经滚动了)提交,控制使用的并行线程的数量等等。这个方法的完整源代码(演示应用程序和可重用库)可以在这里找到。