ListView的分批加载

ListView的分批加载在项目中是非常常见的，一般在用listView显示从网络上获取的资源时，都会用到listView的异步加载和listView的分批加载，好处就不用详细说明了。这里先介绍listView的分批加载。​

布局文件：

main.xml

<?xml version="1.0" encoding="utf-8"?>

< LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical" >

<ListView

        android:layout_width="fill_parent"

        android:layout_height="fill_parent"

        android:id="@+id/listView" />

</LinearLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?>

< LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical" >

<TextView

         android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:textSize="18sp"

    android:textColor="#FFFFFF"

        android:id="@+id/textView"

        />

footer.xml

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

< LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="horizontal" >

<ProgressBar android:id="@+id/c81_forthBar"

        android:layout_width="50dp"

     android:layout_height="wrap_content"

         style="?android:attr/progressBarStyle" />

   < TextView android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:gravity="center_vertical"

    android:textSize="20sp"

    android:text="数据正在加载..."

    />

< /LinearLayout>

Java代码：

Mainactivity.java

package cn.itcast.pageload;

import java.util.ArrayList;

import java.util.List;

import cn.itcast.service.DataService;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.util.Log;

import android.view.View;

import android.widget.AbsListView;

import android.widget.AbsListView.OnScrollListener;

import android.widget.ArrayAdapter;

import android.widget.ListView;

public class MainActivity extends Activity {

    private ListView listView;

    private List<String> data = new ArrayList<String>();

    private  ArrayAdapter<String> adapter;

    private View footer;

    private Handler handler = new Handler(){

  public void handleMessage(Message msg) {

   data.addAll((List<String>) msg.obj);

   adapter.notifyDataSetChanged();//通知ListView数据已经发生改变，要求ListView更新界面显示

   if(listView.getFooterViewsCount()> 0) {

    listView.removeFooterView(footer);

   }

   loadfinish = true;

  }     

    };

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        footer = getLayoutInflater().inflate(R.layout.footer, null);

        listView = (ListView) this.findViewById(R.id.listView);

        listView.setOnScrollListener(new ScrollListener());

        data.addAll(DataService.getData(0, 20));       

        adapter = new ArrayAdapter<String>(this, R.layout.listview_item, R.id.textView, data);

        listView.addFooterView(footer);

        //添加页脚(放在ListView最后),要在setadapter之前添加,否则报错 (原因请看setAdapter()源码)

        //Caused by: java.lang.ClassCastException: android.widget.ArrayAdapter cannot be cast to android.widget.HeaderViewListAdapter

        listView.setAdapter(adapter);

        listView.removeFooterView(footer);

    }

    private int number = 20;//每次获取多少条数据

    private int maxpage = 5;//总共有多少页

    private boolean loadfinish = true;

    //listView滚动事件，可以得到listView滚动到那一条条目位置

    private final class ScrollListener implements OnScrollListener{

  public void onScrollStateChanged(AbsListView view, int scrollState) {

   Log.i("MainActivity", "onScrollStateChanged(scrollState="+ scrollState+ ")");

  }

  public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {

   Log.i("MainActivity", "onScroll(firstVisibleItem="+ firstVisibleItem+ ",visibleItemCount="+

     visibleItemCount+ ",totalItemCount="+ totalItemCount+ ")");

   final int loadtotal = totalItemCount;

   int lastItemid = listView.getLastVisiblePosition();//获取当前屏幕最后Item的ID

   if((lastItemid+1) == totalItemCount){//达到数据的最后一条记录

    if(totalItemCount> 0){

     //当前页

     int currentpage = totalItemCount%number == 0 ? totalItemCount/number : totalItemCount/number+1;

     int nextpage = currentpage + 1;//下一页

     if(nextpage< = maxpage && loadfinish){

      loadfinish = false;

      listView.addFooterView(footer);

      new Thread(new Runnable() {

       public void run() {

        try {

         //模拟网络延迟

         Thread.sleep(3000);

        } catch (InterruptedException e) {

         e.printStackTrace();

        }

        List<String> result = DataService.getData(loadtotal, number);

        handler.sendMessage(handler.obtainMessage(100, result));

       }

      }).start();

     }

    }

   }

  }

    }

}

DataService .java

package cn.itcast.service;

import java.util.ArrayList;

import java.util.List;

public class DataService {

 public static List<String> getData(int offset, int maxResult){//分页 limit 0,20

  List<String> data = new ArrayList<String>();

  for(int i=0 ; i< 20 ; i++){

   data.add("ListView分批加载:"+ i);

  }

  return data;

 }

}