Question

我正在尝试使用片段中的分页来进行无尽的回收视图但面临的问题如下。

findLastCompletlyVisibleItemPosition（）或findFirstCompletelyVisibleItemPosition（）仅返回-1。
如果setNestedScrollingEnabled（false），则onScrollStateChanged无法正常工作

以下是我的代码示例。 `

        recyclerView = (RecyclerView) view.findViewById(R.id.recycler1);

        //recyclerView.setNestedScrollingEnabled(false);                                              // Smooth Scrolling
         mLayoutManager = new LinearLayoutManager(getActivity());

        lastVisiblePosition = mLayoutManager.findLastVisibleItemPosition();
        firstVisibleItemPosition = mLayoutManager.findFirstCompletelyVisibleItemPosition();
        Log.i("sandi", String.valueOf(firstVisibleItemPosition));
        load = new LoadAdapter(getActivity(), grid_list);
        recyclerView.setLayoutManager(mLayoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(load);
        mProgressDialog.dismiss();

        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                int threshold =1;
                int count = recyclerView.getChildCount();



                Log.i("sand", String.valueOf(count));

                if (newState == SCROLL_STATE_IDLE ) {
                    if (lastVisiblePosition >= count
                            - threshold) {
                        // Execute LoadMoreDataTask AsyncTask

                        Log.i("sand","stopped");
                        new LoadMoreDataTask().execute();
                    }
                } else {
                    Log.i("sand","not stopped");
                }
            }

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

修改
这个问题的解决方案在评论部分。

Answer 1

查看LinearLayoutManager

中的第1732至1747行

/**
 * Returns the adapter position of the last fully visible view. This position does not include
 * adapter changes that were dispatched after the last layout pass.
 * <p>
 * Note that bounds check is only performed in the current orientation. That means, if
 * LayoutManager is horizontal, it will only check the view's left and right edges.
 *
 * @return The adapter position of the last fully visible view or
 * {@link RecyclerView#NO_POSITION} if there aren't any visible items.
 * @see #findLastVisibleItemPosition()
 * @see #findFirstCompletelyVisibleItemPosition()
 */

public int findLastCompletelyVisibleItemPosition() {
    final View child = findOneVisibleChild(getChildCount() - 1, -1, true, false);
    return child == null ? NO_POSITION : getPosition(child);
}

如果child为空，则NO_POSITION为-1。

你在做什么：

在设置适配器之前，您正在调用以下内容。没有可用的视图，所以你有-1。

lastVisiblePosition = mLayoutManager.findLastVisibleItemPosition();
firstVisibleItemPosition = mLayoutManager.findFirstCompletelyVisibleItemPosition();

你应该做什么：

当您的适配器视图完全填充时，您可以拥有findLastVisibleItemPosition和findFirstCompletelyVisibleItemPosition。首先设置你的适配器，而不是像

那样获得你的位置

load = new LoadAdapter(getActivity(), grid_list);
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(load);
mProgressDialog.dismiss();
// adapter is set now you may have your positions
lastVisiblePosition = mLayoutManager.findLastVisibleItemPosition();
firstVisibleItemPosition = mLayoutManager.findFirstCompletelyVisibleItemPosition();
Log.i("sandi", String.valueOf(firstVisibleItemPosition));

Answer 2

如果您在recyclerview内使用NestedScrollView，则不会触发recyclerView.addOnScrollListener。我在尝试实现分页时也想到了这一点。而不是我已经为NestedScrollView实现了onScrollChangeListener并使用以下代码完成了这个技巧：

private void implementScrollListener() {

    //Scroll Listener for nestedScrollView. Note that it is used for pagination when user reaches the bottom.

    if(nestedScrollView != null){

        nestedScrollView.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
            @Override
            public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {

                if (scrollY > oldScrollY) {
                    //Scrolling down
                }
                if (scrollY < oldScrollY) {
                    //Scrolling up
                }

                if (scrollY == 0) {
                    //Reaches to the top
                }

                if (scrollY < (v.getChildAt(0).getMeasuredHeight() - v.getMeasuredHeight())) {
                    //Reaches to the bottom so it is time to updateRecyclerView!
                    updateRecyclerView();
                }
            }
        });
    }

}`

Answer 3

我为同一个问题苦苦挣扎了好几个小时，看来您需要在回收者视图上添加globallayoutlistener并将代码放入回调中。

为什么findLastCompletelyVisibleItemPosition（）返回-1？

3 个答案: