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:
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<span style="font-family:Comic Sans MS;">package com.testScroll;
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import android.util.Log;
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import android.view.View;
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import android.widget.AbsListView;
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import android.widget.Toast;
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import android.widget.AbsListView.OnScrollListener;
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public class AutoLoadListener implements OnScrollListener{
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public interface AutoLoadCallBack {
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void execute(String url);
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}
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private int getLastVisiblePosition = 0,lastVisiblePositionY=0;
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private AutoLoadCallBack mCallback;
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public AutoLoadListener(AutoLoadCallBack callback)
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{
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this.mCallback = callback;
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}
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public void onScrollStateChanged(AbsListView view, int scrollState) {
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if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {
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if (view.getLastVisiblePosition() == (view.getCount() - 1)) {
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View v=(View) view.getChildAt(view.getChildCount()-1);
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int[] location = new int[2] ;
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v.getLocationOnScreen(location);
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int y=location [1];
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Log.e("x"+location[0],"y"+location[1]);
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if (view.getLastVisiblePosition()!=getLastVisiblePosition
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&& lastVisiblePositionY!=y)
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{
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Toast.makeText(view.getContext(), "再次拖至底部,即可翻页",500).show();
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getLastVisiblePosition=view.getLastVisiblePosition();
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lastVisiblePositionY=y;
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return;
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}
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else if (view.getLastVisiblePosition()==getLastVisiblePosition
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&& lastVisiblePositionY==y)
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{
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mCallback.execute(">>>>>拖至底部");
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}
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}
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getLastVisiblePosition=0;
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lastVisiblePositionY=0;
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}
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}
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public void onScroll(AbsListView arg0, int arg1, int arg2, int arg3) {
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}
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}
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</span>
主程序为testScroll.java,源码如下:
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<span style="font-family:Comic Sans MS;">package com.testScroll;
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import java.util.ArrayList;
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import java.util.HashMap;
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import com.testScroll.AutoLoadListener.AutoLoadCallBack;
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import android.app.Activity;
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import android.os.Bundle;
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import android.view.View;
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import android.widget.AdapterView;
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import android.widget.AdapterView.OnItemClickListener;
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import android.widget.GridView;
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import android.widget.SimpleAdapter;
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import android.widget.Toast;
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public class testScroll extends Activity {
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@Override
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public void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(R.layout.main);
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setTitle("精确监听AbsListView滚动至底部----hellogv");
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GridView gridview = (GridView) findViewById(R.id.gridview);
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ArrayList<HashMap<String, Object>> lstImageItem = new ArrayList<HashMap<String, Object>>();
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for (int i = 0; i < 30; i++) {
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HashMap<String, Object> map = new HashMap<String, Object>();
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map.put("ItemImage", R.drawable.icon);
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map.put("ItemText", "NO." + String.valueOf(i));
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lstImageItem.add(map);
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}
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SimpleAdapter saImageItems = new SimpleAdapter(this,
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lstImageItem,
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R.layout.night_item,
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new String[] { "ItemImage", "ItemText" },
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new int[] { R.id.ItemImage, R.id.ItemText });
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AutoLoadListener autoLoadListener =new AutoLoadListener(callBack);
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gridview.setOnScrollListener(autoLoadListener);
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gridview.setAdapter(saImageItems);
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gridview.setOnItemClickListener(new ItemClickListener());
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}
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AutoLoadCallBack callBack=new AutoLoadCallBack(){
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public void execute(String url) {
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Toast.makeText(testScroll.this, url, 500).show();
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}
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};
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class ItemClickListener implements OnItemClickListener {
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public void onItemClick(AdapterView<?> arg0,
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View arg1,
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int arg2,
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long arg3
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) {
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HashMap<String, Object> item = (HashMap<String, Object>) arg0
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.getItemAtPosition(arg2);
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setTitle((String) item.get("ItemText"));
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}
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}
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}
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</span>