Adapter传递数据到Activity(接口回调)

public ContactListAdapter(Context context, List<ImpUserInfoVo> list,
QuickAlphabeticBar alpha, HashMap<Integer, Boolean> isSelected) {
this.ctx = context;
this.inflater = LayoutInflater.from(context);
this.list = list;
this.alphaIndexer = new HashMap<String, Integer>();
this.sections = new String[list.size()];
this.isSelected = isSelected;

for (int i = 0; i < list.size(); i++) {
String name = getAlpha(list.get(i).getSortKey());
if (!alphaIndexer.containsKey(name)) {
alphaIndexer.put(name, i);
}
}
mOnClickListener = (OnClickListener) context;
}

public interface OnClickListener {
public void setSelectedNum(int num);
}

mOnClickListener.setSelectedNum(getSelectSize());

public class ContactListActivity extends Activity implements ContactListAdapter.OnClickListener{
}

//接口回调，显示已选择的人数
@Override
public void setSelectedNum(int num) {
haschoose.setText("已经选择" + num + "");
}