<?xml version="1.0" encoding="utf-8"?>

<?xml version="1.0" encoding="utf-8"?>



  

  

<?xml version="1.0" encoding="utf-8"?>



  

  

public class SectionAdapter extends ArrayAdapter {

 private Activity activity;

 public SectionAdapter(Activity activity, String[] objects) {
  super(activity, R.layout.list_item, R.id.label, objects);//为自定义视图指定XML布局文件
  this.activity = activity;
 }

 @Override
 public View getView(int position, View view, ViewGroup parent) {
  if (view == null) {
   view = activity.getLayoutInflater().inflate(R.layout.list_item,
     parent, false);
  }
  TextView header = (TextView) view.findViewById(R.id.header);
  String label = getItem(position);
  if (position == 0//检查列表项起始字母是否发生了改变，如果发生改变，该列表项就是分段中的第一项，修改分段标头的内容并显示该分段标头,否则隐藏
    || getItem(position - 1).charAt(0) != label.charAt(0)) {
   header.setVisibility(View.VISIBLE);
   header.setText(label.substring(0, 1));
  } else {
   header.setVisibility(View.GONE);//隐藏分段标头
  }
  return super.getView(position, view, parent);
 }
}

public class Hack26Activity extends ListActivity {
  private TextView topHeader;//用于访问分段标头
  private int topVisiblePosition = -1;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.list);
    topHeader = (TextView) findViewById(R.id.header);
    setListAdapter(new SectionAdapter(this, Countries.COUNTRIES));
    //设置滚动监听器，当用户滚动列表时，检查位置是否发生了变化，如果改变，调用setTopHeader更新悬浮的分段标头，当列表第一次显示时，确保根据第一个列表项初始化分段标头
    getListView().setOnScrollListener(
        new AbsListView.OnScrollListener() {
          @Override
          public void onScrollStateChanged(AbsListView view,
                           int scrollState) {
            // Empty.
          }

          @Override
          public void onScroll(AbsListView view, int firstVisibleItem,
                     int visibleItemCount, int totalItemCount) {
            if (firstVisibleItem != topVisiblePosition) {
              topVisiblePosition = firstVisibleItem;
              setTopHeader(firstVisibleItem);
            }
          }
        });
    setTopHeader(0);
  }

  private void setTopHeader(int pos) {
    final String text = Countries.COUNTRIES[pos].substring(0, 1);
    topHeader.setText(text);//更新文本内容
  }
}