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

我会尝试扩展使用的LayoutManager(例如LinearLayoutManager)和覆盖scrollVerticallyBy()方法。首先,我会先调用super,然后检查返回的整数值。如果值等于0,则到达底部或顶部边界。然后我将使用findLastVisibleItemPosition()方法来找出到达哪个边界,并在需要时加载更多数据。只是一个想法。

此外,您甚至可以从该方法中返回您的值,允许滚动并显示“loading”指示器。

其他回答

试试下面:

import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.RecyclerView.LayoutManager;

/**
 * Abstract Endless ScrollListener
 * 
 */
public abstract class EndlessScrollListener extends
        RecyclerView.OnScrollListener {
    // The minimum amount of items to have below your current scroll position
    // before loading more.
    private int visibleThreshold = 10;
    // The current offset index of data you have loaded
    private int currentPage = 1;
    // True if we are still waiting for the last set of data to load.
    private boolean loading = true;
    // The total number of items in the data set after the last load
    private int previousTotal = 0;
    private int firstVisibleItem;
    private int visibleItemCount;
    private int totalItemCount;
    private LayoutManager layoutManager;

    public EndlessScrollListener(LayoutManager layoutManager) {
        validateLayoutManager(layoutManager);
        this.layoutManager = layoutManager;
    }

    public EndlessScrollListener(int visibleThreshold,
            LayoutManager layoutManager, int startPage) {
        validateLayoutManager(layoutManager);
        this.visibleThreshold = visibleThreshold;
        this.layoutManager = layoutManager;
        this.currentPage = startPage;
    }

    private void validateLayoutManager(LayoutManager layoutManager)
            throws IllegalArgumentException {
        if (null == layoutManager
                || !(layoutManager instanceof GridLayoutManager)
                || !(layoutManager instanceof LinearLayoutManager)) {
            throw new IllegalArgumentException(
                    "LayoutManager must be of type GridLayoutManager or LinearLayoutManager.");
        }
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        visibleItemCount = recyclerView.getChildCount();
        totalItemCount = layoutManager.getItemCount();
        if (layoutManager instanceof GridLayoutManager) {
            firstVisibleItem = ((GridLayoutManager) layoutManager)
                    .findFirstVisibleItemPosition();
        } else if (layoutManager instanceof LinearLayoutManager) {
            firstVisibleItem = ((LinearLayoutManager) layoutManager)
                    .findFirstVisibleItemPosition();
        }
        if (loading) {
            if (totalItemCount > previousTotal) {
                loading = false;
                previousTotal = totalItemCount;
            }
        }
        if (!loading
                && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
            // End has been reached do something
            currentPage++;
            onLoadMore(currentPage);
            loading = true;
        }
    }

    // Defines the process for actually loading more data based on page
    public abstract void onLoadMore(int page);

}

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。

我会尝试扩展使用的LayoutManager(例如LinearLayoutManager)和覆盖scrollVerticallyBy()方法。首先,我会先调用super,然后检查返回的整数值。如果值等于0,则到达底部或顶部边界。然后我将使用findLastVisibleItemPosition()方法来找出到达哪个边界,并在需要时加载更多数据。只是一个想法。

此外,您甚至可以从该方法中返回您的值,允许滚动并显示“loading”指示器。

我让你接近我。对我来说没问题。

我希望这对你有所帮助。

/**
 * Created by Daniel Pardo Ligorred on 03/03/2016.
 */
public abstract class BaseScrollListener extends RecyclerView.OnScrollListener {

    protected RecyclerView.LayoutManager layoutManager;

    public BaseScrollListener(RecyclerView.LayoutManager layoutManager) {

        this.layoutManager = layoutManager;

        this.init();
    }

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

        super.onScrolled(recyclerView, dx, dy);

        this.onScroll(recyclerView, this.getFirstVisibleItem(), this.layoutManager.getChildCount(), this.layoutManager.getItemCount(), dx, dy);
    }

    private int getFirstVisibleItem(){

        if(this.layoutManager instanceof LinearLayoutManager){

            return ((LinearLayoutManager) this.layoutManager).findFirstVisibleItemPosition();
        } else if (this.layoutManager instanceof StaggeredGridLayoutManager){

            int[] spanPositions = null; //Should be null -> StaggeredGridLayoutManager.findFirstVisibleItemPositions makes the work.

            try{

                return ((StaggeredGridLayoutManager) this.layoutManager).findFirstVisibleItemPositions(spanPositions)[0];
            }catch (Exception ex){

                // Do stuff...
            }
        }

        return 0;
    }

    public abstract void init();

    protected abstract void onScroll(RecyclerView recyclerView, int firstVisibleItem, int visibleItemCount, int totalItemCount, int dx, int dy);

}

没有重复调用,但你滚动。fetchData只会在您位于列表的末尾并且有更多数据要获取时调用

关于我的代码: 1.fetchData()每次调用取10个项。 2.isScrolling是一个类成员变量 3.previousTotalCount也是类成员。它存储以前访问过的最后一个项目

recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
                super.onScrollStateChanged(recyclerView, newState)
                if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
                    isScrolling = true
                }
            }

            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                super.onScrolled(recyclerView, dx, dy)

                val visibleItemCount = layoutManager.childCount
                val totalItemCount = layoutManager.itemCount
                val scrolledOutItems = layoutManager.findFirstVisibleItemPosition()


                if (isScrolling && (visibleItemCount + scrolledOutItems == totalItemCount)
                    && (visibleItemCount + scrolledOutItems != previousTotalCount)) {
                    previousTotalCount = totalItemCount              
                    isScrolling = false
                    fetchData()  //fetches 10 new items from Firestore
                    pagingProgressBar.visibility = View.VISIBLE
                }
            }
        })