Android_开发 ListView分页加载数据
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：
<span style="font-size:13px;"><?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></span>
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 [email protected]
*
*/
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);
}
}
}