android中listview分页加载数据 .

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:

           

<?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:

 

          

<?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：

      

<?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：

       

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：