ListView就是可以显示一行行Item的控件，有时候数据非常多，通常需要分页显示，但为了减少用户的输入，我们可以动态更新ListView，把下一页要显示的数据的添加到当前ListView中。
先看看效果：
需要注意的是在什么时候去更新数据 ，listVIew的setOnScrollListener监听是否滚到了最后一条记录，
取到的数据加到list中，最后记得调用adapter的notifyDataSetChanged，通知listview改变。
不废话，上代码。
主文件：
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ListView;
import android.widget.Toast;
public class ListViewActivity extends Activity {
private ListView listView;
//定义适配器
private ListItemAdapter listadpter;
//定义每一页显示行数
private int VIEW_COUNT = 20;
//定义的页数
private int index = 0;
//当前页
private int currentPage = 1;
//所以数据的条数
private int totalCount;
//每次取的数据，只要最后一次可能不一样。
private int maxResult;
//泛型集合ArrayList
private ArrayList<Students> arrayList = new ArrayList<Students>();
//数据操作的dao类
StudentsDAO dao = new StudentsDAO(ListViewActivity.this);
//实体bean
Students students = new Students();
// 标记：上次的ID
private boolean isUpdating = false;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//初始化界面
initView();
//插入100条记录。
dao.insert();
totalCount = dao.getCount();
maxResult = getMaxResult();
//调用dao里面的selectAll()方法
arrayList = dao.getAllItems(index, maxResult);
//实例化适配器
System.out.println("arrlist-->"+arrayList.size());
listadpter = new ListItemAdapter(ListViewActivity.this,arrayList);
//填充适配器
listView.setAdapter(listadpter);
listView.setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if(firstVisibleItem + visibleItemCount == totalItemCount && !isUpdating){
if(totalItemCount<totalCount){ //防止最后一次取数据进入死循环。
Toast.makeText(ListViewActivity.this, "正在取第"+(++currentPage)+"的数据", Toast.LENGTH_LONG).show();
AsyncUpdateDatasTask asyncUpdateWeiBoDatasTask = new AsyncUpdateDatasTask();
asyncUpdateWeiBoDatasTask.execute();
}
System.out.println("begin update-------------");
}
}
});
}
//初始化界面方法
private void initView() {
// TODO Auto-generated method stub
listView = (ListView) findViewById(R.id.list);
}
class AsyncUpdateDatasTask extends AsyncTask<Void, Void, List<Students>> {
@Override
protected List<Students> doInBackground(Void... params) {
// TODO Auto-generated method stub
isUpdating = true;
index += VIEW_COUNT;
List<Students> list =new ArrayList<Students>();
list = dao.getAllItems(index, maxResult);
return list;
}
@Override
protected void onPostExecute(List<Students> result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
arrayList.addAll(result);
listadpter.notifyDataSetChanged();
isUpdating = false;
System.out.println("end update--------------");
}
}
private int getMaxResult(){
int totalPage = (totalCount+VIEW_COUNT-1)/VIEW_COUNT;
return totalCount-(totalPage-1)*VIEW_COUNT;
}
}
数据库Dao文件：
package com.shao.list;
import java.util.ArrayList;
import java.util.Random;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class StudentsDAO extends SQLiteOpenHelper {
private final static String AUDIODATABASE_NAME = "student.db";
private final static String TABLE = "student";
private final static String COLUM_ID = "id";
private final static String COLUM_NAME = "name";
private final static String COLUM_AGE = "age";
private final static int DATABASE_VERSION = 1;
private long row;
private ArrayList<Students> arrayList;
public StudentsDAO(Context context) {
super(context, AUDIODATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
String sql = "CREATE TABLE " + TABLE + " (" + COLUM_ID
+ " INTEGER primary key autoincrement, " + " " + COLUM_NAME
+ " text, " + " " + COLUM_AGE + " int)";
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
String sql = "DROP TABLE IF EXISTS " + TABLE;
db.execSQL(sql);
}
public long insert() {
SQLiteDatabase db = getWritableDatabase();
ContentValues cv = new ContentValues();
Random random = new Random();
for(int i=1;i<=100;i++)
{
cv.put(COLUM_ID, i);
cv.put(COLUM_NAME, "name"+String.valueOf(i));
cv.put(COLUM_AGE, random.nextInt(100));
row = db.insert(TABLE, null, cv);
}
db.close();
return row;
}
//查询记录的总数
public int getCount() {
SQLiteDatabase db = getWritableDatabase();
String sql = "select count(*) from '"+TABLE+"'";
Cursor c = db.rawQuery(sql, null);
c.moveToFirst();
int length = c.getInt(0);
c.close();
db.close();
// System.out.println("length-->"+length);
return length;
}
public ArrayList<Students> getAllItems(int firstResult, int maxResult) {
arrayList=new ArrayList<Students>();
SQLiteDatabase db = getWritableDatabase();
String sql = "select * from '"+TABLE+"' limit ?,?";
Cursor cursor = db.rawQuery(sql, new String[]{String.valueOf(firstResult), String.valueOf(maxResult)});
if (cursor != null && cursor.getCount() > 0) {
cursor.moveToFirst();
}
for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
Students students=new Students();
students.setId(cursor.getInt(0));
students.setName(cursor.getString(1));
students.setAge(cursor.getInt(2));
arrayList.add(students);
}
cursor.close();
db.close();
return arrayList;
}
public ArrayList<Students> selectAll() {
arrayList=new ArrayList<Students>();
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.query(TABLE, null, null, null, null, null, null);
if (cursor != null && cursor.getCount() > 0) {
cursor.moveToFirst();
}
for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
Students students=new Students();
students.setId(cursor.getInt(0));
students.setName(cursor.getString(1));
students.setAge(cursor.getInt(2));
arrayList.add(students);
}
cursor.close();
db.close();
return arrayList;
}
}
