大家在做字母索引的时候常常会用到SectionIndexer这个类，里面有2个重要的方法
1. getSectionForPosition（）通过该项的位置，获得所在分类组的索引号
2. getPositionForSection() 根据分类列的索引号获得该序列的首个位置
getSectionForPosition(0) 返回 0
getSectionForPosition(1) 返回 0
getSectionForPosition(2) 返回 0
getSectionForPosition(3) 返回 1
这下，明白这两个方法的区别了把
所以一般有如下代码，来确定是否滑动到了分类的首字母位置
- public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
- int totalItemCount) {
- int section = indexer.getSectionForPosition(firstVisibleItem); //获得索引号
- int nextSecPosition = indexer.getPositionForSection(section + 1); //根据索引号获得下一个索引的初始位置
- if (firstVisibleItem != lastFirstVisibleItem) {
- MarginLayoutParams params = (MarginLayoutParams) titleLayout.getLayoutParams();
- params.topMargin = 0;
- titleLayout.setLayoutParams(params);
- title.setText(String.valueOf(alphabet.charAt(section)));
- }
- if (nextSecPosition == firstVisibleItem + 1) { //若是下一个索引号的位置与当前所见的项+1，则进行位移
- View childView = view.getChildAt(0);
- if (childView != null) {
- int titleHeight = titleLayout.getHeight();
- int bottom = childView.getBottom();
- MarginLayoutParams params = (MarginLayoutParams) titleLayout
- .getLayoutParams();
- if (bottom < titleHeight) {
- float pushedDistance = bottom - titleHeight;
- params.topMargin = (int) pushedDistance;
- titleLayout.setLayoutParams(params);
- } else {
- if (params.topMargin != 0) {
- params.topMargin = 0;
- titleLayout.setLayoutParams(params);
- }
- }
- }
- }
- lastFirstVisibleItem = firstVisibleItem;
- }
- });