SectionIndexer中的getSectionForPosition()与getPositionForSection()解惑

转于：http://blog.csdn.net/jack_l1/article/details/14165291

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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;
          }
      });