Android開發教程：OnScrollListener實現ListActivity滾屏首字母提示

OnScrollListener接口是定義在AbsListView中的，而AbsListView的直接子類有GridView和ListView，非直接子類有ExpandableListView。OnScrollListener的完整路徑是frameworks\base\core\java\Android\widget\AbsListView.java，代碼如下：

1. /**
2. * Interface definition for a callback to be invoked when the list or grid
3. * has been scrolled.
4. */
5. public interface OnScrollListener {
7. /**
8. * The view is not scrolling. Note navigating the list using the trackball counts as
9. * being in the idle state since these transitions are not animated.
10. */
11. public static int SCROLL_STATE_IDLE = 0;
13. /**
14. * The user is scrolling using touch, and their finger is still on the screen
15. */
16. public static int SCROLL_STATE_TOUCH_SCROLL = 1;
18. /**
19. * The user had previously been scrolling using touch and had performed a fling. The
20. * animation is now coasting to a stop
21. */
22. public static int SCROLL_STATE_FLING = 2;
24. /**
25. * Callback method to be invoked while the list view or grid view is being scrolled. If the
26. * view is being scrolled, this method will be called before the next frame of the scroll is
27. * rendered. In particular, it will be called before any calls to
28. * {@link Adapter#getView(int, View, ViewGroup)}.
29. *
30. * @param view The view whose scroll state is being reported
31. *
32. * @param scrollState The current scroll state. One of {@link #SCROLL_STATE_IDLE},
33. * {@link #SCROLL_STATE_TOUCH_SCROLL} or {@link #SCROLL_STATE_IDLE}.
34. */
35. public void onScrollStateChanged(AbsListView view, int scrollState);
37. /**
38. * Callback method to be invoked when the list or grid has been scrolled. This will be
39. * called after the scroll has completed
40. * @param view The view whose scroll state is being reported
41. * @param firstVisibleItem the index of the first visible cell (ignore if
42. * visibleItemCount == 0)
43. * @param visibleItemCount the number of visible cells
44. * @param totalItemCount the number of items in the list adaptor
45. */
46. public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
47. int totalItemCount);
48. }