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;}@Overridepublic 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)*/@Overridepublic 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();}@Overridepublic boolean hasStableIds() {return (mAdapter != null) ? mAdapter.hasStableIds() : false;}@Overridepublic boolean isEmpty() {return mAdapter == null || mAdapter.isEmpty();}@Overridepublic int getCount() {int adapterCount = (mAdapter != null) ? mAdapter.getCount() : 0;return getPlaceholdersCount() + adapterCount;}@Overridepublic boolean areAllItemsEnabled() {if (mAdapter != null) {return mAdapter.areAllItemsEnabled();} else {return true;}}@Overridepublic boolean isEnabled(int position) {if (mAdapter != null && position < mAdapter.getCount()) {return mAdapter.isEnabled(position);}return false;}@Overridepublic 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;}@Overridepublic long getItemId(int position) {if (mAdapter != null && position < mAdapter.getCount()) {return mAdapter.getItemId(position);}return -1;}@Overridepublic 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;}@Overridepublic int getItemViewType(int position) {if (mAdapter != null && position < mAdapter.getCount()) {return mAdapter.getItemViewType(position);}return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;}@Overridepublic int getViewTypeCount() {return (mAdapter != null) ? mAdapter.getViewTypeCount() : 1;}@Overridepublic void registerDataSetObserver(DataSetObserver observer) {if (mAdapter != null) {mAdapter.registerDataSetObserver(observer);}}@Overridepublic void unregisterDataSetObserver(DataSetObserver observer) {if (mAdapter != null) {mAdapter.unregisterDataSetObserver(observer);}}@Overridepublic ListAdapter getWrappedAdapter() {return mAdapter;}
}