android ListView结合xutils3仿微信实现下拉加载更多

public class MyOnScrollListener implements OnScrollListener {
 private int totalItemCount;
  //ListView最后的item项
  private int lastItem;
  //listview第一项
  private int firstItem;
  //用于判断当前是否在加载
  private boolean isLoading;
  //底部加载更多布局
  private View footer;
  //接口回调的实例
  private OnloadDataListener listener;
  
  //数据
  private List<MsgBean> data;
  Handler handler = new Handler();
  
  
  public MyOnScrollListener(View footer, List<MsgBean> data) {
  this.footer = footer;
  this.data = data;
  }
  //设置接口回调的实例
  public void setOnLoadDataListener(OnloadDataListener listener) {
  this.listener = listener;
  }
  /**
  * 滑动状态变化
  *
  * @param view
  * @param scrollState 1 SCROLL_STATE_TOUCH_SCROLL是拖动 2 SCROLL_STATE_FLING是惯性滑动 0SCROLL_STATE_IDLE是停止 , 只有当在不同状态间切换的时候才会执行
  */
  @Override
  public void onScrollStateChanged(AbsListView view, int scrollState) {
  //如果数据没有加载，并且滑动状态是停止的,并且滚到了第一个item,可在此做下拉更新或者上拉更新的判断
  if (!isLoading && firstItem == 0 && scrollState == SCROLL_STATE_IDLE) {
   //显示加载更多
   footer.setVisibility(View.VISIBLE);
  
   //模拟一个延迟两秒的刷新功能
   handler.postDelayed(new Runnable() {
   @Override
   public void run() {
    if (listener != null) {
    //开始加载更多数据
    loadMoreData();
    //回调设置ListView的数据
    listener.onLoadData(data);
     //加载完成后操作什么
    loadComplete();
    }
   }
   }, 2000);
  }
  }
  /**
  * 当加载数据完成后，设置加载标志为false表示没有加载数据了
  * 并且设置底部加载更多为隐藏
  */
  private void loadComplete() {
  isLoading = false;
  footer.setVisibility(View.GONE);
  
  }
  /**
  * 开始加载更多新数据，这里每次只更新三条数据
  */
  private void loadMoreData() {
  isLoading = true;
  MsgBean msg = null;
  for (int i = 0; i < 3; i++) {
   msg = new MsgBean();
   msg .setRemark("Liming"+i);
   msg .setMsgID(i);
   data.add(stu);
  }
  }
  /**
  * 监听可见界面的情况
  *
  * @param view  ListView
  * @param firstVisibleItem 第一个可见的 item 的索引
  * @param visibleItemCount 可以显示的 item的条数
  * @param totalItemCount 总共有多少个 item
  */
  @Override
  public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
  //实现下拉加载
  lastItem = firstVisibleItem + visibleItemCount;
   //实现上拉加载
  firstItem = firstVisibleItem;
   //总listView的item个数
  this.totalItemCount = totalItemCount;
  }
  //回调接口
  public interface OnloadDataListener {
  void onLoadData(List<MsgBean> data);
  }
  }

public class ListPageActivity extends Activity implements MyOnScrollListener.OnloadDataListener {
 @Override
  protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_list_page);
 
  //显示到ListView上
  showListView(data);
 //自定义的滚动监听事件
  MyOnScrollListener onScrollListener = new MyOnScrollListener(header, data);
  //设置接口回调
  onScrollListener.setOnLoadDataListener(this);
  //设置ListView的滚动监听事件
  mListView.setOnScrollListener(onScrollListener);

 @Override
  public void onLoadData(List<MsgBean> data) {
  //加载数据完成后，展示数据到ListView
  showListView(data);
  }
}

/**
 * 当前屏幕显示的消息数量
 */
private int MAX_MSG_NUMBER = 20;

private List<MsgBean> getDataFromDb() {

  List<?> dbSize = db.selector(MsgBean.class).where(WhereBuilder.b("id", "=", 400)).findAll();//记得捕获null指针和DbException异常
//如果数据库比我们显示的页数小,则不偏移,否则,偏移到我们需要显示的位置
  if (dbSize.size() < MAX_MSG_NUMBER) {
   indexOffset = 0;
  } else {
   indexOffset = dbSize.size() - MAX_MSG_NUMBER;
  }
  
  List<MsgBean> datas = db.selector(MsgBean.class).where(WhereBuilder.b("id", "=", 400)).limit(MAX_MSG_NUMBER)
     .offset(indexOffset).findAll();
  return datas;
 }

MAX_MSG_NUMBER += MAX_MSG_NUMBER;
getDataFromDb();

/**
 * 数据库 xutils用法
 * @author 青楼爱小生
 */
public class DbUtil {
 private static final String TAG = DbUtil.class.getName();
 private static DbUtil dbUtil;
 private DbManager db;
 private DbUtil(){
  db = x.getDb(MyApplication.getInstance().daoConfig);
 }
 public static DbUtil getInstance(){
  if(dbUtil == null){
   synchronized (DbUtil.class) {
    if(dbUtil == null){
     dbUtil = new DbUtil();
    }
   }
  }
  return dbUtil;
 }
 /**
  * 增加数据
  * @param list
  * @throws DbException 
  */
 public void addMsgList(List<MsgBean> list) {
  try {
   db.saveOrUpdate(list);
  } catch (DbException e) {
   e.printStackTrace();
   LogHelper.e(TAG, e.getMessage());
  }
 }
 /**
  * 增加一条数据
  * @param node
  * @throws DbException
  */
 public void addMsgToDb(MsgBean node) {
  try {
   db.saveOrUpdate(node);
  } catch (DbException e) {
   e.printStackTrace();
   LogHelper.e(TAG, e.getMessage());
  }
 }
 /**
  * 删除表中所有数据
  * @param cls 创建的表的映射
  * @throws DbException 
  */
 public void deleteAll(Class cls) {
  try {
   db.delete(cls);
  } catch (DbException e) {
   LogHelper.e(TAG, e.getMessage());
   e.printStackTrace();
  }
 }
 /**
  * 删除第一条数据
  * @param cls
  */
 @SuppressWarnings("unchecked")
 public void deleteFirst(Class cls){
  try {
   db.delete(db.findFirst(cls));
  } catch (DbException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
 /**
  * 查询表中所有数据
  * @throws DbException 
  */
 @SuppressWarnings("unchecked")
 public List<?> findAll(Class cls) {
  try {
   return db.findAll(cls) == null ? Collections.emptyList() : db.findAll(cls);
  } catch (DbException e) {
  e.printStackTrace();
   LogHelper.e(TAG, e.getMessage());
   return Collections.emptyList();
  }
 }
 /**
  * //添加查询条件进行查询
  List<ChildInfo> all = db.selector(ChildInfo.class).where("id",">",2).and("id","<",4).findAll();
  * @return 搜索指定条件的数据
  */
  @SuppressWarnings("unchecked")
 public List<?> findDataByWhere(Class cls,WhereBuilder format){
  try {
   return db.selector(cls).where(format).findAll()== null ?
     Collections.emptyList() :db.selector(cls).where(format).findAll();
  } catch (DbException e) {
  LogHelper.e(TAG, e.getMessage());
   e.printStackTrace();
   return Collections.emptyList();
  }
 
 }
 /**
  * 添加查询条件进行查询
  * @param cls 表映射
  * @param str select语句
  * @param format where语句
  * @return List<DbModel> DbModel key为数据库列名 value为值
  * eg:(Selector.from(Parent.class) 
         .where("id" ,"<", 54) 
         .and(WhereBuilder.b("age", ">", 20).or("age", " < ", 30)) 
         .orderBy("id") 
         .limit(pageSize) .offset(pageSize * pageIndex)); 
  * 
  * 
  * 
  */
  @SuppressWarnings("unchecked")
 public Selector<?> findDataBySelector(Class cls,WhereBuilder format){
  try {
   return db.selector(cls).where(format);
  } catch (DbException e) {
  // TODO Auto-generated catch block
   e.printStackTrace();
  }
  return null;
 }
  
}