以前對於AdapterView（ListView和GridView的父類）以及這個類的getChildAt（）方法理解十分粗淺，以為是指傳入一個絕對position（就是這個item是AdapterView第幾個元素）來直接獲得到該item，當然,android SDK中對於該方法也沒有很具體的說明。這個理解是錯誤的。以簡單的listview為例先說下listview對於item的複用，一個元素很多的listview，如果頁面的可視區域內最多可以看到6個元素，不妨假如它們的index是0-5,那麼在記憶體中只有6個item物件。當第7個item(即index=6)進入到可視區域的時候，那麼其實是在複用index=0的item。由於在滑動時getView這個更新控制元件的方法執行非常頻繁，所以肉眼是絲毫看不出這種複用的。
那麼，接著上面的例子來說，任何情況下，getChildAt（int position)返回的item都是指的可視區域內的第position個元素。下面是一種巧妙和嚴謹的方法可以在任何時候（指的是listView滑動在任意狀態時）根據position取得可視區域內的item，如果該item不在可視區域，則返回null。

private static class ChildViewInfo {

        private Integer firstVisiblePosition = null;
        private Integer childCount = null;

        private Integer headerViewsCount = null;

        private Integer firstVisiblePositionWithOutHeaderViews = null;
        private Integer childCountWithOutHeaderViews = null
 
;
        private Integer visibleHeaderViewsCount = null;

        public ChildViewInfo(AdapterView<Adapter> adapterView) {
            Adapter adapter = adapterView.getAdapter();
            firstVisiblePosition = adapterView.getFirstVisiblePosition();
            childCount = adapterView.getChildCount();
            if
 
 (null != adapter && adapter instanceof HeaderViewListAdapter) {
                headerViewsCount = ((HeaderViewListAdapter) adapter).getHeadersCount();

                firstVisiblePositionWithOutHeaderViews = firstVisiblePosition - headerViewsCount;
                if (firstVisiblePositionWithOutHeaderViews < 0) {
                    firstVisiblePositionWithOutHeaderViews = 0;
                }

                visibleHeaderViewsCount = headerViewsCount - firstVisiblePosition;
                if (visibleHeaderViewsCount > 0) {
                    visibleHeaderViewsCount = Math.min(childCount, visibleHeaderViewsCount);
                    childCountWithOutHeaderViews = childCount - visibleHeaderViewsCount;
                } else {
                    visibleHeaderViewsCount = 0;
                    childCountWithOutHeaderViews = childCount;
                }
            }
        }


        public View getItemView(int position, boolean withOutHeaderViews) { 
            boolean b = withOutHeaderViews && adapterView.getAdapter() instanceof HeaderViewListAdapter;
            ChildViewInfo childViewInfo = new ChildViewInfo(adapterView);
            int firstVisiblePosition = b ? childViewInfo.firstVisiblePositionWithOutHeaderViews : 
                childViewInfo.firstVisiblePosition;
            int childCount = b ? childViewInfo.childCountWithOutHeaderViews : 
                childViewInfo.childCount;
            Integer index = getItemViewIndex(firstVisiblePosition, childCount, position);
            if (null != index) {
                index = b ? index + childViewInfo.visibleHeaderViewsCount : index;
                return adapterView.getChildAt(index);
            }
            return null;
        }

        public static Integer getItemViewIndex(int firstVisiblePosition, int childCount, int position) {
            int index = position - firstVisiblePosition;
            int count = childCount;
            if (index >= 0 && index < count) {
                return index;
            }
            return null;
        }
}