GridView翻页

GridView翻页(精确监听AbsListView滚动至底部)

2011-08-11 16:28:33

标签： 移动开发 休闲 Android 职场 GridView翻页

本文来自http://blog.csdn.net/hellogv/ ，引用必须注明出处！

       用户使用android客户端时，当ListView滚动至底部，可以由一个按钮来提示用户是否读下一页，那么如果使用GridView呢？现在很多WEB 2.0上的体验就是当底部时自动读取下一页数据，GridView(ListView也可)可以采用这种方法。网上已经有很多文章介绍了如何判断ListView是否滚动至底部，原理是 AbsListView.getLastVisiblePosition() = (AbsListView.getCount() - 1) 即到底，如果往上拖一点，用户看起来已经离开底部，但实际上 AbsListView.getLastVisiblePosition() == (AbsListView.getCount() - 1) 依然成立，会导致误判断。本文在它们基础上加以改进，做到更精确地监听是否滚动至底部。先来看看本文程序运行的效果：

原理是在AbsListView.getLastVisiblePosition() = =(AbsListView.getCount() - 1) 时，保存最后一个Item的绝对坐标，如果两次获取的绝对Y值都一样，即到底然后执行回调函数......源码如下：

import android.view.View;
import android.widget.AbsListView;
import android.widget.Toast;
import android.widget.AbsListView.OnScrollListener;

/**
* 滚动至列表底部，读取下一页数据
*/
public class AutoLoadListener implements OnScrollListener {

   public interface AutoLoadCallBack {
     void execute();
  }

   private int getLastVisiblePosition = 0, lastVisiblePositionY = 0;
   private AutoLoadCallBack mCallback;

   public AutoLoadListener(AutoLoadCallBack callback) {
     this.mCallback = callback;
  }

   public void onScrollStateChanged(AbsListView view, int scrollState) {

     if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {
       //滚动到底部    
       if (view.getLastVisiblePosition() == (view.getCount() - 1)) {
        View v = (View) view.getChildAt(view.getChildCount() - 1);
         int[] location = new int[2];
        v.getLocationOnScreen(location); //获取在整个屏幕内的绝对坐标    
         int y = location[1];

        MyLog.d( "x" + location[0], "y" + location[1]);
         if (view.getLastVisiblePosition() != getLastVisiblePosition && lastVisiblePositionY != y) //第一次拖至底部    
        {
          Toast.makeText(view.getContext(), "已经拖动至底部，再次拖动即可翻页", 500).show();
          getLastVisiblePosition = view.getLastVisiblePosition();
          lastVisiblePositionY = y;
           return;
        } else if (view.getLastVisiblePosition() == getLastVisiblePosition && lastVisiblePositionY == y) //第二次拖至底部    
        {
          mCallback.execute();
        }
      }

       //未滚动到底部，第二次拖至底部都初始化    
      getLastVisiblePosition = 0;
      lastVisiblePositionY = 0;
    }
  }

   public void onScroll(AbsListView arg0, int arg1, int arg2, int arg3) {

  }
}

主程序为testScroll.java，源码如下：

public class testScroll extends Activity {    
         /** Called when the activity is first created. */    
        @Override    
         public void onCreate(Bundle savedInstanceState) {    
                 super.onCreate(savedInstanceState);    
                setContentView(R.layout.main);    
                setTitle( "精确监听AbsListView滚动至底部----hellogv");    
                GridView gridview = (GridView) findViewById(R.id.gridview);    
    
                 // 生成动态数组，并且转入数据    
                ArrayList<HashMap<String, Object>> lstImageItem = new ArrayList<HashMap<String, Object>>();    
                 for ( int i = 0; i < 30; i++) {    
                        HashMap<String, Object> map = new HashMap<String, Object>();    
                        map.put( "ItemImage", R.drawable.icon); // 添加图像资源的ID    
                        map.put( "ItemText", "NO." + String.valueOf(i)); // 按序号做ItemText    
                        lstImageItem.add(map);    
                }    
                 // 生成适配器的ImageItem <====> 动态数组的元素，两者一一对应    
                SimpleAdapter saImageItems = new SimpleAdapter( this, // 没什么解释    
                                lstImageItem, // 数据来源    
                                R.layout.night_item, // night_item的XML实现    
    
                                 // 动态数组与ImageItem对应的子项    
                                 new String[] { "ItemImage", "ItemText" },    
    
                                 // ImageItem的XML文件里面的一个ImageView,两个TextView ID    
                                 new int[] { R.id.ItemImage, R.id.ItemText });    
                    
                 //添加自动读页的事件    
                AutoLoadListener autoLoadListener = new AutoLoadListener(callBack);    
                gridview.setOnScrollListener(autoLoadListener);    
                 // 添加并且显示    
                gridview.setAdapter(saImageItems);    
                 // 添加消息处理    
                gridview.setOnItemClickListener( new ItemClickListener());    
        }    
    
        AutoLoadCallBack callBack= new AutoLoadCallBack(){    
    
                 public void execute() {    
                        Toast.makeText(testScroll. this, "滚动至底部", 500).show();    
                }    
                    
        };    
         // 当AdapterView被单击(触摸屏或者键盘)，则返回的Item单击事件    
         class ItemClickListener implements OnItemClickListener {    
                 public void onItemClick(AdapterView<?> arg0, // The AdapterView where the    
                                                                                                         // click happened    
                                View arg1, // The view within the AdapterView that was clicked    
                                 int arg2, // The position of the view in the adapter    
                                 long arg3 // The row id of the item that was clicked    
                ) {    
                         // 在本例中arg2=arg3    
                        HashMap<String, Object> item = (HashMap<String, Object>) arg0    
                                        .getItemAtPosition(arg2);    
                         // 显示所选Item的ItemText    
                        setTitle((String) item.get( "ItemText"));    
                }