Android ListView combined with xutils3 imitation WeChat to implement drop-down loading more

public class MyOnScrollListener implements OnScrollListener {
 private int totalItemCount;
  //The last item of ListView  private int lastItem;
  //listview item 1  private int firstItem;
  // Used to determine whether it is currently loading  private boolean isLoading;
  //Load more layouts at the bottom  private View footer;
  //Instance of interface callback  private OnloadDataListener listener;
  
  //data  private List<MsgBean> data;
  Handler handler = new Handler();
  
  
  public MyOnScrollListener(View footer, List<MsgBean> data) {
   = footer;
   = data;
  }
  //Set an instance of interface callback  public void setOnLoadDataListener(OnloadDataListener listener) {
   = listener;
  }
  /**
   * Change of sliding state
   *
   * @param view
   * @param scrollState 1 SCROLL_STATE_TOUCH_SCROLL is dragging 2 SCROLL_STATE_FLING is inertial sliding 0SCROLL_STATE_IDLE is stopping, only when switching between different states
   */
  @Override
  public void onScrollStateChanged(AbsListView view, int scrollState) {
  //If the data is not loaded and the sliding state is stopped and it rolls to the first item, you can make a decision to update the pull-down or pull-up update.  if (!isLoading && firstItem == 0 && scrollState == SCROLL_STATE_IDLE) {
   //Show more loading   ();
  
   //Simulate a refresh function with two seconds delay   (new Runnable() {
   @Override
   public void run() {
    if (listener != null) {
    //Start loading more data    loadMoreData();
    //Callback sets ListView data    (data);
     //What to do after loading is completed    loadComplete();
    }
   }
   }, 2000);
  }
  }
  /**
   * When the loading data is completed, setting the loading flag to false means that there is no data loading.
   * And set the bottom load more to hide
   */
  private void loadComplete() {
  isLoading = false;
  ();
  
  }
  /**
   * Start loading more new data, here only three pieces of data are updated at a time
   */
  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);
   (stu);
  }
  }
  /**
   * Listen to visible interface
   *
   * @param view ListView
   * @param firstVisibleItem index of the first visible item
   * @param visibleItemCount The number of items that can be displayed
   * @param totalItemCount How many items are there in total
   */
  @Override
  public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
  //Implement drop-down loading  lastItem = firstVisibleItem + visibleItemCount;
   //Implement pull-up loading  firstItem = firstVisibleItem;
   //Total listView items   = totalItemCount;
  }
  //Callback interface  public interface OnloadDataListener {
  void onLoadData(List<MsgBean> data);
  }
  }

public class ListPageActivity extends Activity implements  {
 @Override
  protected void onCreate(Bundle savedInstanceState) {
  (savedInstanceState);
  setContentView(.activity_list_page);
 
  //Show to ListView  showListView(data);
 //Custom scrolling listening events  MyOnScrollListener onScrollListener = new MyOnScrollListener(header, data);
  //Set the interface callback  (this);
  //Set the scroll listening event of ListView  (onScrollListener);

 @Override
  public void onLoadData(List<MsgBean> data) {
  //After loading data is completed, display the data to ListView  showListView(data);
  }
}

/**
  * Number of messages currently displayed on the screen
  */
private int MAX_MSG_NUMBER = 20;

private List<MsgBean> getDataFromDb() {

  List<?> dbSize = ().where(("id", "=", 400)).findAll();//Remember to catch null pointer and DbException exception//If the database is smaller than the number of pages we display, it will not be offset, otherwise, it will be offset to the position we need to display  if (() < MAX_MSG_NUMBER) {
   indexOffset = 0;
  } else {
   indexOffset = () - MAX_MSG_NUMBER;
  }
  
  List<MsgBean> datas = ().where(("id", "=", 400)).limit(MAX_MSG_NUMBER)
     .offset(indexOffset).findAll();
  return datas;
 }

MAX_MSG_NUMBER += MAX_MSG_NUMBER;
getDataFromDb();

/**
  * Database xutils usage
  * @author Brothel Loves Young Student
  */
public class DbUtil {
 private static final String TAG = ();
 private static DbUtil dbUtil;
 private DbManager db;
 private DbUtil(){
  db = (().daoConfig);
 }
 public static DbUtil getInstance(){
  if(dbUtil == null){
   synchronized () {
    if(dbUtil == null){
     dbUtil = new DbUtil();
    }
   }
  }
  return dbUtil;
 }
 /**
   * Add data
   * @param list
   * @throws DbException
   */
 public void addMsgList(List<MsgBean> list) {
  try {
   (list);
  } catch (DbException e) {
   ();
   (TAG, ());
  }
 }
 /**
   * Add one data
   * @param node
   * @throws DbException
   */
 public void addMsgToDb(MsgBean node) {
  try {
   (node);
  } catch (DbException e) {
   ();
   (TAG, ());
  }
 }
 /**
   * Delete all data in the table
   * @param cls Mapping of tables created
   * @throws DbException
   */
 public void deleteAll(Class cls) {
  try {
   (cls);
  } catch (DbException e) {
   (TAG, ());
   ();
  }
 }
 /**
   * Delete the first piece of data
   * @param cls
   */
 @SuppressWarnings("unchecked")
 public void deleteFirst(Class cls){
  try {
   ((cls));
  } catch (DbException e) {
   // TODO Auto-generated catch block
   ();
  }
 }
 /**
   * Query all data in the table
   * @throws DbException
   */
 @SuppressWarnings("unchecked")
 public List<?> findAll(Class cls) {
  try {
   return (cls) == null ? () : (cls);
  } catch (DbException e) {
  ();
   (TAG, ());
   return ();
  }
 }
 /**
   * //Add query conditions for query
   List<ChildInfo> all = ().where("id",">",2).and("id","<",4).findAll();
   * @return Search for data for specified criteria
   */
  @SuppressWarnings("unchecked")
 public List&lt;?&gt; findDataByWhere(Class cls,WhereBuilder format){
  try {
   return (cls).where(format).findAll()== null ?
     () :(cls).where(format).findAll();
  } catch (DbException e) {
  (TAG, ());
   ();
   return ();
  }
 
 }
 /**
   * Add query conditions to query
   * @param cls table mapping
   * @param str select statement
   * @param format where statement
   * @return List<DbModel> DbModel key is the database column name value is the value
   * eg:(()
          .where("id" ,"<", 54)
          .and(("age", ">", 20).or("age", " < ", 30))
          .orderBy("id")
          .limit(pageSize) .offset(pageSize * pageIndex));
   *
   *
   *
   */
  @SuppressWarnings("unchecked")
 public Selector&lt;?&gt; findDataBySelector(Class cls,WhereBuilder format){
  try {
   return (cls).where(format);
  } catch (DbException e) {
  // TODO Auto-generated catch block
   ();
  }
  return null;
 }
  
}