android中listview分页加载数据

来源：互联网发布：程序员笔记软件知乎编辑：程序博客网时间：2024/04/28 23:46

首先说下listview的优化方案，这也是面试中常考的题目。优化方案有三种：1,如果自定义适配器，那么在getView方法中判断contentView是否为空，如果为空创建contentView并返回，如果不为空直接返回contentView。这样能尽可能少创建view。2.给contentView设置tag，传入一个viewHoder对象，用于缓存要实现的数据。3，如果listview中显示的item太多，就要考虑分页加载了。

下面就注意介绍一下分页加载数据。首先在layout下创建listview.xml:

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<?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" >  
  
    <ListView  
        android:id="@+id/listView1"  
        android:layout_width="match_parent"  
        android:layout_height="wrap_content" >  
    </ListView>  
  
</LinearLayout>  

然后创建listview_item.xml:

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<?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">    
    <TextView    
        android:id="@+id/list_item_text"    
        android:layout_width="fill_parent"    
        android:layout_height="fill_parent"    
        android:gravity="center"    
        android:textSize="20sp"    
        android:paddingTop="10dp"    
        android:paddingBottom="10dp"/>    
</LinearLayout>    

再为跟多按钮添加一个xml：

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<?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="wrap_content"  
    android:gravity="center"  
    android:orientation="vertical" >  
  
    <Button  
        android:id="@+id/loadMoreButton"  
        android:layout_width="fill_parent"  
        android:layout_height="wrap_content"  
        android:onClick="loadMore"  
        android:text="加载更多" />  
  
</LinearLayout>  

代码部分：

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public class ListViewAdapter extends BaseAdapter {  
  
    private static Map<Integer,View> m=new HashMap<Integer,View>();  
      
    private List<String> items;  
    private LayoutInflater inflater;  
      
    public ListViewAdapter(List<String> items, Context context) {  
        super();  
        this.items = items;  
        this.inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);  
    }  
  
    @Override  
    public int getCount() {  
        // TODO Auto-generated method stub  
        return items.size();  
    }  
  
    @Override  
    public Object getItem(int position) {  
        // TODO Auto-generated method stub  
        return items.get(position);  
    }  
  
    @Override  
    public long getItemId(int position) {  
        // TODO Auto-generated method stub  
        return position;  
    }  
  
    @Override  
    public View getView(int position, View contentView, ViewGroup arg2) {  
        // TODO Auto-generated method stub  
        contentView=m.get(position);  
        if(contentView==null){  
            contentView=inflater.inflate(R.layout.listview_item, null);  
            TextView text=(TextView) contentView.findViewById(R.id.list_item_text);  
            text.setText(items.get(position));  
        }  
        m.put(position, contentView);  
        return contentView;  
    }  
      
    public void addItem(String item) {    
        items.add(item);    
    }    
  
}  

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public class ListViewActivity extends Activity implements OnScrollListener  {  
      List<String> items = new ArrayList<String>();    
     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 ListViewAdapter adapter;    
        private View loadMoreView;    
        private Button loadMoreButton;    
        private Handler handler = new Handler();    
        
        @Override    
        public void onCreate(Bundle savedInstanceState) {    
            super.onCreate(savedInstanceState);    
            setContentView(R.layout.listview);    
                
            loadMoreView = getLayoutInflater().inflate(R.layout.load_more, null);    
            loadMoreButton = (Button) loadMoreView.findViewById(R.id.loadMoreButton);    
            loadMoreButton.setOnClickListener(new OnClickListener() {  
                  
                @Override  
                public void onClick(View v) {  
                    // TODO Auto-generated method stub  
                    loadMoreButton.setText("正在加载...");   //设置按钮文字loading    
                    handler.postDelayed(new Runnable() {    
                        @Override    
                        public void run() {    
                                
                            loadData();    
                                
                            adapter.notifyDataSetChanged(); //数据集变化后,通知adapter    
                            listView.setSelection(visibleLastIndex - visibleItemCount + 1); //设置选中项    
                                
                            loadMoreButton.setText("加载更多");    //恢复按钮文字    
                        }    
                    }, 1000);    
                }  
            });  
            listView = (ListView) this.findViewById(R.id.listView1);  
                
            listView.addFooterView(loadMoreView);   //设置列表底部视图    
           // listView.addHeaderView(v)    //设置列表顶部视图  
        
            initAdapter();    
                
            listView.setAdapter(adapter);                //自动为id是list的ListView设置适配器    
                
            listView.setOnScrollListener(this);     //添加滑动监听    
            listView.setOnItemClickListener(new OnItemClickListener() {  
  
                @Override  
                public void onItemClick(AdapterView<?> arg0, View view,  
                        int position, long arg3) {  
                    // TODO Auto-generated method stub  
                    Toast.makeText(getApplicationContext(), items.get(position),Toast.LENGTH_SHORT).show();  
                }  
            });  
        }    
            
        /**   
         * 初始化适配器   
         */    
        private void initAdapter() {    
           
            for (int i = 0; i < 20; i++) {    
                items.add(String.valueOf(i + 1));    
            }    
            adapter = new ListViewAdapter(items,this);    
        }    
        
        /**   
         * 滑动时被调用   
         */    
        @Override    
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {    
            this.visibleItemCount = visibleItemCount;    
            visibleLastIndex = firstVisibleItem + visibleItemCount - 1;    
        }    
        
        /**   
         * 滑动状态改变时被调用   
         */    
        @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;             //加上底部的loadMoreView项    
            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    
                Log.i("LOADMORE", "loading...");    
            }    
        }    
            
  
        /**   
         * 模拟加载数据   
         */    
        private void loadData() {    
            int count = adapter.getCount();    
            for (int i = count; i < count + 20; i++) {    
                adapter.addItem(String.valueOf(i + 1));    
            }    
        }  
  
          
}  

最后看看效果：

原文链接：http://blog.csdn.net/wangkuifeng0118/article/details/7252423