android中listview分页载入数据

               前段时间做的新浪微博项目一直想实现listview分页载入数据，今天最终实现了，哈哈！感觉挺好的，今天又写了个demo给大家分享下。

              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,假设自己定义适配器，那么在getView方法中推断contentView是否为空，假设为空创建contentView并返回，假设不为空直接返回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，假设listview中显示的item太多，就要考虑分页载入了。

               以下就注意介绍一下分页载入数据。首先在layout下创建listview.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" >

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

</LinearLayout>

<?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button加入一个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="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="载入很多其它" />

</LinearLayout>

           代码部分：

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);  
    }  

}

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;       // 当前窗体可见项总数  
	    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("正在载入...");   //设置button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("载入很多其它");    //恢复button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);                //自己主动为id是list的ListView设置适配器  
	          
	        listView.setOnScrollListener(this);     //加入滑动监听  
	        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) {  
	            //假设是自己主动载入,能够在这里放置异步载入数据的代码  
	            Log.i("LOADMORE", "loading...");  
	        }  
	    }  
	      

	    /** 
	     * 模拟载入数据 
	     */  
	    private void loadData() {  
	        int count = adapter.getCount();  
	        for (int i = count; i < count + 20; i++) {  
	            adapter.addItem(String.valueOf(i + 1));  
	        }  
	    }

		
}