Question

android的分批加载是怎么实现的

Answer 1

每次滑动至底端，从数据库中获取10条数据，并加载于ListView中
数据库

package com.example.listviewbatchloading;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class PersonDb extends SQLiteOpenHelper {

public PersonDb(Context context) {
super(context, "creature", null, 1);
// TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("create table people(_id integer primary key autoincrement,name char,number char)");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("drop table people");
onCreate(db);
}

}

数据库的业务封装，其中获取更多数据的是核心代码

package com.example.listviewbatchloading;

/**
* 数据库的业务封装类
*/

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class PersonList {

PersonDb personDb;

public PersonList(Context context){
this.personDb = new PersonDb(context);
}

/**
* 获取一定条目的数据
* @param startIndex
* 开始取数据的位置
* @param num
* 取多少条数据
*/
public List<Person> getMoreDatas(int startIndex,int num){

List<Person> list = new ArrayList<Person>();
SQLiteDatabase db = personDb.getWritableDatabase();
Cursor cursor = db.rawQuery("select name,number from people order by _id desc limit ?,?",
new String[]{startIndex + "",num + ""});

while(cursor.moveToNext()){
Person person = new Person();
person.setName(cursor.getString(cursor.getColumnIndex("name")));
person.setNumber(cursor.getString(cursor.getColumnIndex("number")));
list.add(person);
}

cursor.close();
db.close();

return list;

}

/**
* 添加数据库条目
* @param name
* @param number
*/
public void add(String name,String number){

SQLiteDatabase db = personDb.getWritableDatabase();

ContentValues cv = new ContentValues();
cv.put("name", name);
cv.put("number", number);

db.insert("people", null, cv);
db.close();
}

}

功能实现

package com.example.listviewbatchloading;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

private ListView lv ;
private List<Person> datas = new ArrayList<Person>();
private static int PERPAGE = 10; //每页加载数目
private static final int FINISH = 0;//数据加载完成
private List<Person> moreDatas;//每次加载的数据
private MyAdapter adapter;
private PersonList personList ;

//若数据较多，耗时较长，数据加载完成时，发送FINISH至handler，并通知ListView更新数据
private Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {

switch (msg.what) {
case FINISH:
if (moreDatas.size() != 0) {
System.out.println(moreDatas.toString());
adapter.notifyDataSetChanged();
}else {
Toast.makeText(MainActivity.this, "没有更多数据", Toast.LENGTH_SHORT).show();
}
break;

default:
break;
}

};
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initData();
initEvent();
}
/**
* 为ListView添加滚动监听事件，但滚动至最后一行时，加载更多数据
*/
private void initEvent() {
lv.setOnScrollListener(new OnScrollListener() {

@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {
int lastVisiblePosition = lv.getLastVisiblePosition();
if (lastVisiblePosition == datas.size() - 1) {
initData();
System.out.println("加载更多数据");
}
}
}

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub

}
});
}

private void initView() {

setContentView(R.layout.activity_main);

lv = (ListView) findViewById(R.id.lv);
personList = new PersonList(getApplicationContext());
adapter = new MyAdapter();
lv.setAdapter(adapter);
}

/**
* 在子线程中加载数据，避免主线程阻塞
*/
private void initData() {
new Thread() {

public void run() {

// 加载更多数据
moreDatas = personList.getMoreDatas(datas.size(), PERPAGE);

datas.addAll(moreDatas);// 把一个容器的所有数据加进来
// 取数据完成，发消息通知取数据完成
handler.obtainMessage(FINISH).sendToTarget();

};
}.start();
}

private class ItemView{
private TextView tv_name;
private TextView tv_num;
}

/**
* ListView的适配器
* @author lian
*
*/
private class MyAdapter extends BaseAdapter{

@Override
public int getCount() {
// TODO Auto-generated method stub
return datas.size();
}

@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return null;
}

@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return 0;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

ItemView itemView = null;
if (convertView == null) {
itemView = new ItemView();
convertView = View.inflate(getApplicationContext(), R.layout.item_lv, null);
itemView.tv_name = (TextView) convertView.findViewById(R.id.tv_name);
itemView.tv_num = (TextView) convertView.findViewById(R.id.tv_num);
convertView.setTag(itemView);
}else {
itemView = (ItemView) convertView.getTag();
}

Person person = datas.get(position);
itemView.tv_name.setText(person.getName());
itemView.tv_num.setText(person.getNumber());

return convertView;
}

}

}