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 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。