import ...

/**
 * Detect scroll events of list or grid.
 */
public class ScrollDetector implements OnScrollListener {
    /** @see #onScroll(android.widget.AbsListView, int, int, int) */
    private boolean mFirstItemVisible = false;
    private OnFirstItemScrollListener mFisListener;
    private OnLastItemVisibleListener mLivListener;

    public ScrollDetector(OnFirstItemScrollListener fisListener,
            OnLastItemVisibleListener livListener) {
        mFisListener = fisListener;
        mLivListener = livListener;
    }

    public void setOnFirstItemScrollListener(OnFirstItemScrollListener listener) {
        mFisListener = listener;
    }

    public void setOnLastItemVisibleListener(OnLastItemVisibleListener listener) {
        mLivListener = listener;
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        if (mLivListener != null) {
            if (triggerLastItemVisible(view, scrollState)) {
                mLivListener.onLastItemVisible();
            }
        }
    }

    private boolean triggerLastItemVisible(AbsListView view, int scrollState) {
        return (scrollState == SCROLL_STATE_IDLE &&
                (view.getLastVisiblePosition() == view.getCount() - 1));
    }

    /**
     * 用超高的初速度滚动AbsListView时, 可能会出现跳过firstVisibleItem=0的情况, 因此,
     * 通过设置mFirstItemVisible来避免在出现上述情况时不会调用onFirstItemScroll的问题
     *
     * @see OnScrollListener#onScroll(android.widget.AbsListView, int, int, int)
     */
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        if (mFisListener != null) {
            if (triggerFirstItemScroll(view, firstVisibleItem) || mFirstItemVisible) {
                mFisListener.onFirstItemScroll(view.getChildAt(0));
                if (!mFirstItemVisible) {
                    mFirstItemVisible = true;
                }
            } else {
                if (mFirstItemVisible) {
                    mFirstItemVisible = false;
                }
            }
        }
    }

    private boolean triggerFirstItemScroll(AbsListView view, int firstVisibleItem) {
        return (firstVisibleItem == 0);
    }

    public static interface OnLastItemVisibleListener {
        void onLastItemVisible();
    }

    public static interface OnFirstItemScrollListener {
        void onFirstItemScroll(View itemView);
    }
}

import ...

/**
 * PlaceholderListAdapter可以帮助我们解决这样的问题:<br> <ul><li>当所有Item视图不足以占满ListView时,
 * 用空白视图来填充空白区域.</li></ul><br> 效果图见微博Android客户端的微博正文页面. 该适配器主要是用来提升用户体验的,
 * 尤其是在切换TAB时.
 *
 * @see android.widget.HeaderViewListAdapter
 */
public class PlaceholderListAdapter implements WrapperListAdapter {
    private final ListAdapter mAdapter;

    public class FixedViewInfo {
        public View view;
        public Object data;
        public boolean isSelectable;
    }

    private ArrayList<FixedViewInfo> mFooterViewInfos;
    private View mPinnedHeaderView;

    public PlaceholderListAdapter(Context context, ListAdapter adapter) {
        mAdapter = adapter;
        mFooterViewInfos = new ArrayList<FixedViewInfo>();
        init(context);
    }

    private void init(Context context) {
        View placeholder = new View(context);
        placeholder.setLayoutParams(
                new AbsListView.LayoutParams(
                        LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
        addFooterView(placeholder, true);
    }

    public void setPinnedHeaderView(View view) {
        mPinnedHeaderView = view;
    }

    public void addFooterView(View view) {
        addFooterView(view, false);
    }

    private void addFooterView(View view, boolean isPlaceholder) {
        FixedViewInfo info = new FixedViewInfo();
        info.view = view;
        info.data = null;
        info.isSelectable = true;
        if (isPlaceholder) {
            mFooterViewInfos.add(info);
        } else {
            mFooterViewInfos.add(mFooterViewInfos.size() - 1, info);
        }
    }

    public int getPlaceholdersCount() {
        return mFooterViewInfos.size();
    }

    @Override
    public boolean hasStableIds() {
        return (mAdapter != null) ? mAdapter.hasStableIds() : false;
    }

    @Override
    public boolean isEmpty() {
        return mAdapter == null || mAdapter.isEmpty();
    }

    @Override
    public int getCount() {
        int adapterCount = (mAdapter != null) ? mAdapter.getCount() : 0;
        return getPlaceholdersCount() + adapterCount;
    }

    @Override
    public boolean areAllItemsEnabled() {
        if (mAdapter != null) {
            return mAdapter.areAllItemsEnabled();
        } else {
            return true;
        }
    }

    @Override
    public boolean isEnabled(int position) {
        if (mAdapter != null && position < mAdapter.getCount()) {
            return mAdapter.isEnabled(position);
        }
        return false;
    }

    @Override
    public Object getItem(int position) {
        int adapterCount = 0;
        if (mAdapter != null) {
            adapterCount = mAdapter.getCount();
            if (position < adapterCount) {
                return mAdapter.getItem(position);
            }
        }

        return mFooterViewInfos.get(position - adapterCount).data;
    }

    @Override
    public long getItemId(int position) {
        if (mAdapter != null && position < mAdapter.getCount()) {
            return mAdapter.getItemId(position);
        }

        return -1;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        int adapterCount = 0;
        if (mAdapter != null) {
            adapterCount = mAdapter.getCount();
            if (position < adapterCount) {
                return mAdapter.getView(position, convertView, parent);
            }
        }

        View view = mFooterViewInfos.get(position - adapterCount).view;
        if (position == getCount() - 1) {// 当convertView为占位View时
            if (!(parent instanceof ListView)) {
                throw new IllegalArgumentException("the parent is not a ListView.");
            }

            ListView listView = (ListView) parent;
            int startPosition = listView.getHeaderViewsCount();
            int itemsHeight = (mPinnedHeaderView != null) ? mPinnedHeaderView.getHeight() : 0;
            int firstVisiblePos = listView.getFirstVisiblePosition();
            int lastVisiblePos = listView.getLastVisiblePosition();
            if (startPosition >= firstVisiblePos) {// 第一个数据视图还在屏幕上, 此时需要占位视图
                for (int i = startPosition; i <= lastVisiblePos; ++i) {
                    View childView = listView.getChildAt(i - firstVisiblePos);
                    itemsHeight += childView.getHeight();
                }
            } else {// 第一个数据视图已经滚出屏幕, 此时不需要显示占位视图
                itemsHeight = listView.getHeight();
            }

            ViewGroup.LayoutParams params = view.getLayoutParams();
            if (params == null) {
                throw new IllegalArgumentException("the layout parameters is not set.");
            }

            params.height = listView.getHeight() - itemsHeight;
            //view.setLayoutParams(params);
        }

        return view;
    }

    @Override
    public int getItemViewType(int position) {
        if (mAdapter != null && position < mAdapter.getCount()) {
            return mAdapter.getItemViewType(position);
        }
        return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;
    }

    @Override
    public int getViewTypeCount() {
        return (mAdapter != null) ? mAdapter.getViewTypeCount() : 1;
    }

    @Override
    public void registerDataSetObserver(DataSetObserver observer) {
        if (mAdapter != null) {
            mAdapter.registerDataSetObserver(observer);
        }
    }

    @Override
    public void unregisterDataSetObserver(DataSetObserver observer) {
        if (mAdapter != null) {
            mAdapter.unregisterDataSetObserver(observer);
        }
    }

    @Override
    public ListAdapter getWrappedAdapter() {
        return mAdapter;
    }
}