ActivityGroup + GridView 实现Tab分页标签

本人推荐采用这种办法去做,而不是系统提供的TabHost和TabActivity,感觉它们使用起来不自由! 
请参考: 
http://blog.csdn.net/hellogv/archive/2010/12/06/6057174.aspx 

      很多客户端软件和浏览器软件都喜欢用Tab分页标签来搭建界面框架。读者也许会马上想到使用TabHost 与 TabActivity的组合，其实最常用的不是它们，而是由GridView与ActivityGroup的组合。每当用户在GridView选中一项，ActivityGroup就把该项对应的Activity的Window作为View添加到ActivityGroup所指定的容器(LinearLayout)中。 

接下来贴出本例运行的效果图： 

 

ImageAdapter是本实例的关键之一，它继承于BaseAdapter，并加入一些自定义的方法。ImageAdapter的源码如下： 

import android.content.Context;
import android.graphics.drawable.ColorDrawable;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
/**
 *
 * @author GV
 *
 */
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]);
        }
    }

    public int getCount() {
        return imgItems.length;
    }

    public Object getItem(int position) {
        return position;
    }

    public long getItemId(int position) {
        return position;
    }

    /**
     * 设置选中的效果
     */
    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
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            imageView=imgItems[position];
        } else {
            imageView = (ImageView) convertView;
        }
        return imageView;
    }
}

SetFocus(int)这个方法是个关键点，即实现选中的效果。例如有ABCD4个Item，其中C被选中了，那么除C以外的Item都被设置为未被选中的样式，而C则设置为选中的样式。 


接下来就开始写主Activity，主Activity包含GridView控件，名为gvTopBar，有2点是需要注意一下的。 

SetNumColumns()：必须要使用setNumColumns来设置列数，因为这个GridView只有一行，即所有的Item都在同一行，Item数量即为列数。 
setSelector(new ColorDrawable(Color.TRANSPARENT))：把系统默认选中的背景色透明化，因为我们已经在BaseAdapter中加入了SetFocus()来改变选中的样式。 

import android.app.Activity;
import android.app.ActivityGroup;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.util.Log;
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.Toast;
import android.widget.AdapterView.OnItemClickListener;
/**
 *
 * @author GV
 *
 */
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_user, R.drawable.topbar_shoppingcart,
            R.drawable.topbar_note };

    @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.topbar_itemselector);
        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 || id == 2) {
            intent = new Intent(ActivityGroupDemo.this, ActivityA.class);
        } else if (id == 1 || id == 3) {
            intent = new Intent(ActivityGroupDemo.this, ActivityB.class);
        }
        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);
    }

}

主Activity的布局XML文件源码如下： 

<?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: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>