? 用戶使用android客戶端時，當ListView滾動至底部，可以由一個按鈕來提示用戶是否讀下一頁，那么如果使用GridView呢？現在很多WEB 2.0上的體驗就是當底部時自動讀取下一頁數據，GridView(ListView也可)可以采用這種方法。網上已經有很多文章介紹了如何判斷ListView是否滾動至底部，原理是 AbsListView.getLastVisiblePosition() = (AbsListView.getCount() - 1) 即到底，如果往上拖一點，用戶看起來已經離開底部，但實際上 AbsListView.getLastVisiblePosition()?== (AbsListView.getCount() - 1) 依然成立，會導致誤判斷。本文在它們基礎上加以改進，做到更精確地監聽是否滾動至底部。先來看看本文程序運行的效果：

?

本文在?Android入門第八篇之GridView(九宮圖)基礎上加入滾到事件判斷，文件名為AutoLoadListener.java，原理是在AbsListView.getLastVisiblePosition() = =(AbsListView.getCount() - 1) 時，保存最后一個Item的絕對坐標，如果兩次獲取的絕對Y值都一樣，即到底然后執行回調函數......源碼如下：

[java]?view plaincopyprint?

<span?style="font-family:Comic?Sans?MS;">package?com.testScroll;??

??

import?android.util.Log;??

import?android.view.View;??

import?android.widget.AbsListView;??

import?android.widget.Toast;??

import?android.widget.AbsListView.OnScrollListener;??

/**?

?*?滾動至列表底部，讀取下一頁數據?

?*/??

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)?{??

????????????//滾動到底部??

????????????if?(view.getLastVisiblePosition()?==?(view.getCount()?-?1))?{??

????????????????View?v=(View)?view.getChildAt(view.getChildCount()-1);??

????????????????int[]?location?=?new??int[2]?;??

????????????????v.getLocationOnScreen(location);//獲取在整個屏幕內的絕對坐標??

????????????????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，即可翻頁",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");??

????????????????}??

????????????}??

??????????????

????????????//未滾動到底部，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)?{??

??????????

????}??

}??

</span>??

主程序為testScroll.java，源碼如下：

[java]?view plaincopyprint?

<span?style="font-family:Comic?Sans?MS;">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("精確監聽AbsListView滾動至底部----hellogv");??

????????GridView?gridview?=?(GridView)?findViewById(R.id.gridview);??

??

????????//?生成動態數組，并且轉入數據??

????????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);//?添加圖像資源的ID??

????????????map.put("ItemText",?"NO."?+?String.valueOf(i));//?按序號做ItemText??

????????????lstImageItem.add(map);??

????????}??

????????//?生成適配器的ImageItem?<====>?動態數組的元素，兩者一一對應??

????????SimpleAdapter?saImageItems?=?new?SimpleAdapter(this,?//?沒什么解釋??

????????????????lstImageItem,//?數據來源??

????????????????R.layout.night_item,//?night_item的XML實現??

??

????????????????//?動態數組與ImageItem對應的子項??

????????????????new?String[]?{?"ItemImage",?"ItemText"?},??

??

????????????????//?ImageItem的XML文件里面的一個ImageView,兩個TextView?ID??

????????????????new?int[]?{?R.id.ItemImage,?R.id.ItemText?});??

???????????

????????//添加自動讀頁的事件??

????????AutoLoadListener?autoLoadListener?=new?AutoLoadListener(callBack);??

????????gridview.setOnScrollListener(autoLoadListener);??

????????//?添加并且顯示??

????????gridview.setAdapter(saImageItems);??

????????//?添加消息處理??

????????gridview.setOnItemClickListener(new?ItemClickListener());??

????}??

??

????AutoLoadCallBack?callBack=new?AutoLoadCallBack(){??

??

????????public?void?execute(String?url)?{??

????????????Toast.makeText(testScroll.this,?url,?500).show();??

????????}??

??????????

????};??

????//?當AdapterView被單擊(觸摸屏或者鍵盤)，則返回的Item單擊事件??

????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);??

????????????//?顯示所選Item的ItemText??

????????????setTitle((String)?item.get("ItemText"));??

????????}??

??

????}??

}??

</span> ?

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