Android中ListView分页加载数据

鉴客 发布于 2011/11/14 13:43
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Android应用开发中,采用ListView组件来展示数据是很常用的功能,当一个应用要展现很多的数据时,一般情况下都不会把所有的数据一次就展示出来,而是通过分页的形式来展示数据,个人觉得这样会有更好的用户体验。因此,很多应用都是采用分批次加载的形式来获取用户所需的数据。例如:微博客户端可能会在用户滑动至列表底端时自动加载下一页数据,也可能在底部放置一个"查看更多"按钮,用户点击后,加载下一页数据。

下面通过一个Demo来展示ListView功能如何实现:该Demo通过在ListView列表的底部添加一个“查看更多...”按钮来加载新闻(模拟新闻客户端)分页数据。同时限定每次加载10条记录,但完全加载完数据后,就把ListView列表底部视图“查看更多...”删除。假设加载的数据总数为 38 条记录。先看下该Demo工程的程序结构图:


其中包 com.andyidea.bean中News.java类是新闻实体类,包com.andyidea.listview中 paginationListViewActivity.java类是用来展示ListView列表。布局layout中包含三个布局文件,分别为:list_item.xml , loadmore.xml , main.xml 。下面分别贴下源码:

layout中的 list_item.xml源码:

<?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">
  <TextView
     android:id="@+id/newstitle"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"/>
  <TextView
     android:id="@+id/newscontent"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"/>
</LinearLayout>

layout中loadmore.xml源码:

<?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">
  <Button  
      android:id="@+id/loadMoreButton"  
      android:layout_width="fill_parent"  
      android:layout_height="wrap_content"
      android:text="查看更多..." /> 
</LinearLayout>

layout中main.xml源码:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <ListView
       android:id="@+id/lvNews"
       android:layout_width="fill_parent"
       android:layout_height="wrap_content"/>
</LinearLayou

包 com.andyidea.bean中News.java类源码:
package com.andyidea.bean;

/**
 * 新闻实体类
 * @author Andy.Chen
 * @mail Chenjunjun.ZJ@gmail.com
 *
 */
public class News {
	
	private String title;    //标题
	private String content;  //内容
	
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public String getContent() {
		return content;
	}
	public void setContent(String content) {
		this.content = content;
	}

}

包com.andyidea.listview中paginationListViewActivity.java类源码:
package com.andyidea.listview;

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

import com.andyidea.bean.News;

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

public class PaginationListViewActivity extends Activity implements OnScrollListener {
	
	private ListView listView;  
    private int visibleLastIndex = 0;   //最后的可视项索引  
    private int visibleItemCount;       // 当前窗口可见项总数  
    private int datasize = 38;          //模拟数据集的条数
    private PaginationAdapter adapter;  
    private View loadMoreView;  
    private Button loadMoreButton;  
    private Handler handler = new Handler(); 
	
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        loadMoreView = getLayoutInflater().inflate(R.layout.loadmore, null);
        loadMoreButton = (Button)loadMoreView.findViewById(R.id.loadMoreButton);
        loadMoreButton.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				loadMoreButton.setText("正在加载中...");   //设置按钮文字
				handler.postDelayed(new Runnable() {
					
					@Override
					public void run() {
						loadMoreData();
						adapter.notifyDataSetChanged();
						loadMoreButton.setText("查看更多...");  //恢复按钮文字
					}
				},2000);
				
			}
		});
        
        listView = (ListView)findViewById(R.id.lvNews);
        listView.addFooterView(loadMoreView);    //设置列表底部视图
        initializeAdapter();
        listView.setAdapter(adapter);
        listView.setOnScrollListener(this);
    }
    
    @Override
	public void onScrollStateChanged(AbsListView view, int scrollState) {
		int itemsLastIndex = adapter.getCount()-1;  //数据集最后一项的索引  
		int lastIndex = itemsLastIndex + 1;
		if (scrollState == OnScrollListener.SCROLL_STATE_IDLE
				&& visibleLastIndex == lastIndex) {
			// 如果是自动加载,可以在这里放置异步加载数据的代码
		}
	}


	@Override
	public void onScroll(AbsListView view, int firstVisibleItem,
			int visibleItemCount, int totalItemCount) {
		this.visibleItemCount = visibleItemCount;
		visibleLastIndex = firstVisibleItem + visibleItemCount - 1;
		
		Log.e("========================= ","========================");
		Log.e("firstVisibleItem = ",firstVisibleItem+"");
		Log.e("visibleItemCount = ",visibleItemCount+"");
		Log.e("totalItemCount = ",totalItemCount+"");
		Log.e("========================= ","========================");
		
		//如果所有的记录选项等于数据集的条数,则移除列表底部视图
		if(totalItemCount == datasize+1){
			listView.removeFooterView(loadMoreView);
			Toast.makeText(this, "数据全部加载完!", Toast.LENGTH_LONG).show();
		}
	}
	
	/**
	 * 初始化ListView的适配器
	 */
	private void initializeAdapter(){
		List<News> news = new ArrayList<News>();
		for(int i=1;i<=10;i++){
			News items = new News();
			items.setTitle("Title"+i);
			items.setContent("This is News Content"+i);
			news.add(items);
		}
		adapter = new PaginationAdapter(news);
	}
	
	/**
	 * 加载更多数据
	 */
	private void loadMoreData(){
		int count = adapter.getCount();
		
		if(count+10 <= datasize){
			for(int i=count+1; i<=count+10; i++){
				News item = new News();
				item.setTitle("Title"+i);
				item.setContent("This is News Content"+i);
				adapter.addNewsItem(item);
			}
		}else{
			for(int i=count+1; i<=datasize; i++){
				News item = new News();
				item.setTitle("Title"+i);
				item.setContent("This is News Content"+i);
				adapter.addNewsItem(item);
			}
		}
		
	}
    
    
    class PaginationAdapter extends BaseAdapter{
    	
    	List<News> newsItems;
    	
    	public PaginationAdapter(List<News> newsitems){
    		this.newsItems = newsitems;
    	}

		@Override
		public int getCount() {
			return newsItems.size();
		}

		@Override
		public Object getItem(int position) {
			return newsItems.get(position);
		}

		@Override
		public long getItemId(int position) {
			return position;
		}

		@Override
		public View getView(int position, View view, ViewGroup parent) {
			if(view == null){
				view = getLayoutInflater().inflate(R.layout.list_item, null);
			}
			
			//新闻标题
			TextView tvTitle = (TextView)view.findViewById(R.id.newstitle);
			tvTitle.setText(newsItems.get(position).getTitle());
			//新闻内容
			TextView tvContent = (TextView)view.findViewById(R.id.newscontent);
			tvContent.setText(newsItems.get(position).getContent());
			
			return view;
		}
		
		/**
		 * 添加数据列表项
		 * @param newsitem
		 */
		public void addNewsItem(News newsitem){
			newsItems.add(newsitem);
		}
    	
    }

}

最后,运行程序的结果截图如下:

通过上面的截图,当我们点击"查看更多..."按钮时,就会加载下10条记录,当加载完所有的记录后,ListView的底部视图将会移除。

文章出处:http://blog.csdn.net/cjjky/article/details/6898871

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