精确监听AbsListView滚动至底部

 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：

 

本文在 Android入门第八篇之GridView(九宫图)基础上加入滚到事件判断，文件名为AutoLoadListener.java，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：

package com.testScroll;import android.util.Log;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(String url);}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];        Log.e("x"+location[0],"y"+location[1]);if (view.getLastVisiblePosition()!=getLastVisiblePosition&& lastVisiblePositionY!=y)//第一次拖至底部{Toast.makeText(view.getContext(), "再次拖至底部，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(">>>>>拖至底部");}}//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：

package com.testScroll;import java.util.ArrayList;import java.util.HashMap;import com.testScroll.AutoLoadListener.AutoLoadCallBack;import android.app.Activity;import android.os.Bundle;import android.view.View;import android.widget.AdapterView;import android.widget.AdapterView.OnItemClickListener;import android.widget.GridView;import android.widget.SimpleAdapter;import android.widget.Toast;public class testScroll extends Activity {/** Called when the activity is first created. */@Overridepublic 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IDmap.put("ItemText", "NO." + String.valueOf(i));// 按序号做ItemTextlstImageItem.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 IDnew 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(String url) {Toast.makeText(testScroll.this, url, 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 happenedView arg1,// The view within the AdapterView that was clickedint arg2,// The position of the view in the adapterlong arg3// The row id of the item that was clicked) {// 在本例中arg2=arg3HashMap<String, Object> item = (HashMap<String, Object>) arg0.getItemAtPosition(arg2);// 显示所选Item的ItemTextsetTitle((String) item.get("ItemText"));}}}