Android 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:
需要注意的是程序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。
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; } } </students></students></students></students></void,></students></students>
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; } } </students></students></students></students></students>