ActivityGroup的讲解！和顶部tabhost的效果是一样

package com.ActivityGroupDemo;

import android.app.ActivityGroup;  
import android.content.Intent;  
import android.graphics.Color;  
import android.graphics.drawable.ColorDrawable;  
import android.os.Bundle;  
import android.view.Gravity;  
import android.view.View;  
import android.view.Window;  
import android.view.ViewGroup.LayoutParams;  
import android.widget.AdapterView;  
import android.widget.GridView;  
import android.widget.LinearLayout;  
import android.widget.AdapterView.OnItemClickListener;  
public class ActivityGroupDemo extends ActivityGroup {
	 private GridView gvTopBar;  
	    private ImageAdapter topImgAdapter;  
	    public LinearLayout container;// 装载sub Activity的容器  
	  
	    /** 顶部按钮图片 **/  
	    int[] topbar_image_array = { R.drawable.topbar_home,  
	            R.drawable.topbar_home, R.drawable.topbar_home};  
	  
	    @Override  
	    public void onCreate(Bundle savedInstanceState) {  
	        super.onCreate(savedInstanceState);  
	        setContentView(R.layout.main);  
	        gvTopBar = (GridView) this.findViewById(R.id.gvTopBar);  
	        gvTopBar.setNumColumns(topbar_image_array.length);// 设置每行列数  
	        gvTopBar.setSelector(new ColorDrawable(Color.TRANSPARENT));// 选中的时候为透明色  
	        gvTopBar.setGravity(Gravity.CENTER);// 位置居中  
	        gvTopBar.setVerticalSpacing(0);// 垂直间隔  
	        int width = this.getWindowManager().getDefaultDisplay().getWidth()  
	                / topbar_image_array.length;  
	        topImgAdapter = new ImageAdapter(this, topbar_image_array, width, 48,  
	                R.drawable.app_icon);  
	        gvTopBar.setAdapter(topImgAdapter);// 设置菜单Adapter  
	        gvTopBar.setOnItemClickListener(new ItemClickEvent());// 项目点击事件  
	        container = (LinearLayout) findViewById(R.id.Container);  
	        SwitchActivity(0);//默认打开第0页  
	    }  
	  
	    class ItemClickEvent implements OnItemClickListener {  
	  
	        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,  
	                long arg3) {  
	            SwitchActivity(arg2);  
	        }  
	    }  
	    /** 
	     * 根据ID打开指定的Activity 
	     * @param id GridView选中项的序号 
	     */  
	    void SwitchActivity(int id)  
	    {  
	        topImgAdapter.SetFocus(id);//选中项获得高亮  
	        container.removeAllViews();//必须先清除容器中所有的View  
	        Intent intent =null;  
	        if (id == 0 ) {  
	            intent = new Intent(ActivityGroupDemo.this, ActivityA.class);  
	        } else if (id == 1 ) {  
	        	intent = new Intent(ActivityGroupDemo.this, ActivityB.class);  
	        }   else if (id == 2) {  
	            intent = new Intent(ActivityGroupDemo.this, ActivityC.class);  
	        } else  {  
	           
	        }  
	        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);  
	        //Activity 转为 View  
	        Window subActivity = getLocalActivityManager().startActivity(  
	                "subActivity", intent);  
	        //容器添加View  
	        container.addView(subActivity.getDecorView(),  
	                LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);  
	    }  
}

<?xml version="1.0" encoding="utf-8"?>  
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
        android:orientation="vertical" android:layout_width="fill_parent"  
        android:background="#ff8866"
        android:layout_height="fill_parent">  
        <RelativeLayout android:layout_height="fill_parent"  
            android:layout_width="fill_parent">  
            <GridView android:layout_height="wrap_content" android:id="@+id/gvTopBar"  
                android:layout_alignParentTop="true" android:layout_width="fill_parent"  
                android:fadingEdgeLength="5dip" android:fadingEdge="vertical">  
            </GridView>  
            <LinearLayout android:id="@+id/Container"  
                android:layout_below="@+id/gvTopBar" android:layout_width="fill_parent"  
                android:layout_height="fill_parent">  
            </LinearLayout>  
        </RelativeLayout>  
    </LinearLayout>  

package com.ActivityGroupDemo;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class ImageAdapter extends BaseAdapter {

	private Context mContext;   
    private ImageView[] imgItems;  
    private int selResId;  
    public ImageAdapter(Context c,int[] picIds,int width,int height,int selResId) {   
        mContext = c;   
        this.selResId=selResId;  
        imgItems=new ImageView[picIds.length];  
        for(int i=0;i<picIds.length;i++)  
        {  
            imgItems[i] = new ImageView(mContext);   
            imgItems[i].setLayoutParams(new GridView.LayoutParams(width, height));//设置ImageView宽高   
            imgItems[i].setAdjustViewBounds(false);   
            //imgItems[i].setScaleType(ImageView.ScaleType.CENTER_CROP);   
            imgItems[i].setPadding(2, 2, 2, 2);   
            imgItems[i].setImageResource(picIds[i]);   
        }  
    }   
	
	@Override
	public int getCount() {
		// TODO Auto-generated method stub
		return  imgItems.length;
	}

	@Override
	public Object getItem(int position) {
		// TODO Auto-generated method stub
		return position;
	}

	@Override
	public long getItemId(int position) {
		// TODO Auto-generated method stub
		return position;
	}

	public void SetFocus(int index)    
    {    
        for(int i=0;i<imgItems.length;i++)    
        {    
            if(i!=index)    
            {    
                imgItems[i].setBackgroundResource(0);//恢复未选中的样式  
            }    
        }    
        imgItems[index].setBackgroundResource(selResId);//设置选中的样式  
    }    
      @Override
    public View getView(int position, View convertView, ViewGroup parent) {   
        ImageView imageView;   
        if (convertView == null) {   
            imageView=imgItems[position];  
        } else {   
            imageView = (ImageView) convertView;   
        }   
        return imageView;   
    }   

}

源码在我的资源里         http://download.csdn.net/source/3446963