精确监听AbsListView滚动至底部

最后更新于:2022-04-01 15:47:40

 本文来自[http://blog.csdn.net/hellogv/](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: ![](https://docs.gechiui.com/gc-content/uploads/sites/kancloud/2016-06-24_576cb0a7b46b5.gif)   本文在 [Android入门第八篇之GridView(九宫图)](http://blog.csdn.net/hellogv/article/details/4567095)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. */ @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(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 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")); } } } ~~~  
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