Android中下拉加载的实现

Android中下拉加载的实现

                                                                                                                     2013-08-04      16:12:21

  最近在做项目的过程中，需要用到下拉加载的功能。总结了一下下拉加载实现的实现。

  首先，我们在main.xml中加入一个listview

 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">

    <ListView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/lvNews"/>

</LinearLayout>

  然后，设置listview中每一个item的布局item.xml

 

<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:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/newstitle"/>

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/newscontent"/>
</LinearLayout>

 以上的对item的布局实现的是每一个item中放置了一上一下的两个Textview

 最后我们设置一个Button，这个Button加在listview的下面，是用来实现点击加载的  loadmore.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/loadMoreButton"
        android:text="查看更多..."/>

</LinearLayout>

 

  接下来是下拉加载的实现代码，首先，类要继承OnScrollListener，继承该接口需要实现两个重载方法：onScrollStateChanged（）、onScroll（）。下面直接上代码，代码中有详细的注解。

 

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.activity_pagination_list_view);
        
        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);
        }
        
    }

}

 通过以上的代码就可以实现下拉加载的效果了，显示效果如下图所示。当点击查看更多时listview会在后面加载10条记录，直到记录加载完毕，加载按钮会消失，并且提示用户已经加载完毕。