前段時間做的新浪微博專案一直想實現listview分頁載入資料，今天終於實現了，哈哈！感覺挺好的，今天又寫了個demo給大家分享下。

              首先說下listview的優化方案，這也是面試中常考的題目。優化方案有三種：1,如果自定義介面卡，那麼在getView方法中判斷contentView是否為空，如果為空建立contentView並返回，如果不為空直接返回contentView。這樣能儘可能少建立view。2.給contentView設定tag，傳入一個viewHoder物件，用於快取要實現的資料。3，如果listview中顯示的item太多，就要考慮分頁載入了。

               下面就注意介紹一下分頁載入資料。首先在layout下建立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>  
 

           再為跟多按鈕新增一個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="載入更多" />

</LinearLayout>

           程式碼部分：

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;   //最後的可視項索引  
	    private int visibleItemCount;       // 當前視窗可見項總數  
	    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("正在載入...");   //設定按鈕文字loading  
			        handler.postDelayed(new Runnable() {  
			            @Override  
			            public void run() {  
			                  
			                loadData();  
			                  
			                adapter.notifyDataSetChanged(); //資料集變化後,通知adapter  
			                listView.setSelection(visibleLastIndex - visibleItemCount + 1); //設定選中項  
			                  
			                loadMoreButton.setText("載入更多");    //恢復按鈕文字  
			            }  
			        }, 1000);  
				}
			});
	        listView = (ListView) this.findViewById(R.id.listView1);
	          
	        listView.addFooterView(loadMoreView);   //設定列表底部檢視  
	       // listView.addHeaderView(v)    //設定列表頂部檢視
	  
	        initAdapter();  
	          
	        listView.setAdapter(adapter);                //自動為id是list的ListView設定介面卡  
	          
	        listView.setOnScrollListener(this);     //新增滑動監聽  
	        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();
				}
			});
	    }  
	      
	    /** 
	     * 初始化介面卡 
	     */  
	    private void initAdapter() {  
	     
	        for (int i = 0; i < 20; i++) {  
	            items.add(String.valueOf(i + 1));  
	        }  
	        adapter = new ListViewAdapter(items,this);  
	    }  
	  
	    /** 
	     * 滑動時被呼叫 
	     */  
	    @Override  
	    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {  
	        this.visibleItemCount = visibleItemCount;  
	        visibleLastIndex = firstVisibleItem + visibleItemCount - 1;  
	    }  
	  
	    /** 
	     * 滑動狀態改變時被呼叫 
	     */  
	    @Override  
	    public void onScrollStateChanged(AbsListView view, int scrollState) {  
	        int itemsLastIndex = adapter.getCount() - 1;    //資料集最後一項的索引  
	        int lastIndex = itemsLastIndex + 1;             //加上底部的loadMoreView項  
	        if (scrollState == OnScrollListener.SCROLL_STATE_IDLE && visibleLastIndex == lastIndex) {  
	            //如果是自動載入,可以在這裡放置非同步載入資料的程式碼  
	            Log.i("LOADMORE", "loading...");  
	        }  
	    }  
	      

	    /** 
	     * 模擬載入資料 
	     */  
	    private void loadData() {  
	        int count = adapter.getCount();  
	        for (int i = count; i < count + 20; i++) {  
	            adapter.addItem(String.valueOf(i + 1));  
	        }  
	    }

		
}