GridView翻页(精确监听AbsListView滚动至底部)

[align=center]本文来自http://blog.csdn.net/hellogv/ ，引用必须注明出处！[/align]
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) {

}

}

<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;
/**
* 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) {

}
}
</span>
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"));

}

}

}