如何使用framelayout

小弟日前参照网上的资料写了点android代码，刚开始布局文件用的是linearlayout，但是显示有问题，后来把最外层改为framelayout,就显示正常了，现在我把布局文件和源代码贴出来，求大神们帮我看看，到底是为什么显示不出来，顺便给小弟介绍一下framelayout如何使用，小弟在此感激了。
下面是main.xml文件：<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:scrollbars="vertical" >

<LinearLayout 
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    >
    <include android:id="@+id/header_layout_id"
        layout="@layout/header_layout"/>
    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager_id"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        />
</LinearLayout>
    
    <LinearLayout 
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <RelativeLayout 
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            >
            <LinearLayout 
                android:id="@+id/bottomviewgroup_id"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal"
                android:layout_alignParentBottom="true"
                android:gravity="center_horizontal"
                android:layout_marginBottom="40dip"
                ></LinearLayout>
        </RelativeLayout>
    </LinearLayout>
    
</LinearLayout>
下面是header_layout.xml文件：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/top_layout"
    android:layout_width="fill_parent"
    android:layout_height="66px"
    android:background="@drawable/top_back_image" 
    >
    <LinearLayout 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:layout_alignParentLeft="true"
        android:layout_centerVertical="true">
        <Button 
            android:id="@+id/backbutton"
            android:layout_width="71px"
            android:layout_height="45px"
            android:textColor="#ffffff"
            android:layout_marginLeft="5dip"
            android:background="@drawable/btn_back_bg"
            android:gravity="center"
            android:text="@string/backbutton"/>
    </LinearLayout>
    <LinearLayout 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_centerVertical="true"
        >
        <Button 
            android:id="@+id/homebutton"
            android:layout_width="71px"
            android:layout_height="45px"
            android:text="@string/homebutton"
            android:textColor="#ffffff"
            android:gravity="center"
            android:layout_marginRight="5dip"
            android:background="@drawable/btn_home_bg"
            />
    </LinearLayout>
</RelativeLayout>
下面是源代码：
package billy.viewpagerdemo2;import java.util.ArrayList;import android.app.Activity;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.view.Window;
import android.widget.ImageView;public class ViewPagerDemo2Activity extends Activity {

private LayoutInflater inflater;
private ViewGroup mainViewGroup;
// private ViewPager myViewPager;
private ViewGroup indicaterViewGroup;
private ArrayList<View> viewList;
private ImageView[] myImageViews;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.main);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        
        //获得一个inflater
        inflater = getLayoutInflater();
        //载入main布局
        mainViewGroup = (ViewGroup)inflater.inflate(R.layout.main, null);
        //底端的页面指示图标
        indicaterViewGroup = (ViewGroup)mainViewGroup.findViewById(R.id.bottomviewgroup_id);
        
        viewList = new ArrayList<View>();
        viewList.add(inflater.inflate(R.layout.layout_item_01, null));
        viewList.add(inflater.inflate(R.layout.layout_item_02, null));
        viewList.add(inflater.inflate(R.layout.layout_item_03, null));
        viewList.add(inflater.inflate(R.layout.layout_item_04, null));
        viewList.add(inflater.inflate(R.layout.layout_item_05, null));
        viewList.add(inflater.inflate(R.layout.layout_item_06, null));
        
        //开辟底端页面指示图标的图片数组
        myImageViews = new ImageView[viewList.size()];
        //给数据赋值
        for(int i = 0; i < myImageViews.length ; i ++){
         ImageView temp_imImageView = new ImageView(this);
         temp_imImageView.setLayoutParams(new LayoutParams(20, 20));
         temp_imImageView.setPadding(20, 0, 20, 0);
        
         if(i == 0){
         temp_imImageView.setBackgroundResource(R.drawable.page_indicator_focused);
         }else{
         temp_imImageView.setBackgroundResource(R.drawable.page_indicator);
         }
         myImageViews[i] = temp_imImageView;
         indicaterViewGroup.addView(myImageViews[i]);
        }
        //显示
        setContentView(mainViewGroup);
        
        
    }
}