Android Tabhostについて

import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.LinearLayout;
import android.widget.TabHost;
import android.widget.TabWidget;
import android.widget.TextView;

public class MainActivity extends FragmentActivity {
    ViewPager viewPager;
    TabHost tabHost;
    View indicator;
    TabWidget tabWidget;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //マテリアルデザインの作業
        tabWidget = (TabWidget) findViewById(android.R.id.tabs);
        tabWidget.setStripEnabled(false);
        tabWidget.setShowDividers(LinearLayout.SHOW_DIVIDER_NONE);
        indicator = findViewById(R.id.indicator);

        tabHost = (TabHost) findViewById(android.R.id.tabhost);
        tabHost.setup();

        getActionBar().setElevation(0);     //TabとActionBarとの間の影を消す

        float elevation = 4 * getResources().getDisplayMetrics().density;
        tabHost.setElevation(elevation);

        //PagerとTabの設定
        ViewPagerAdapter vpa = new ViewPagerAdapter(getSupportFragmentManager());
        viewPager = (ViewPager) findViewById(R.id.pager);
        viewPager.setAdapter(vpa);
        viewPager.setOnPageChangeListener(new PageChangeListener());

        for (int i = 0; i < vpa.getCount(); i++) {
            tabHost.addTab(tabHost
                    .newTabSpec(String.valueOf(i))
                    .setIndicator(vpa.getPageTitle(i))
                    .setContent(android.R.id.tabcontent));
        }

        LayoutInflater inflater = LayoutInflater.from(this);
        for (int i = 0; i < vpa.getCount(); i++) {
            TextView tv = (TextView) inflater.inflate(R.layout.tab_widget, tabWidget, false);
            tv.setText(vpa.getPageTitle(i));

            tabHost.addTab(tabHost
                    .newTabSpec(String.valueOf(i))
                    .setIndicator(tv)
                    .setContent(android.R.id.tabcontent));
        }


        tabHost.setOnTabChangedListener(new TabHost.OnTabChangeListener() {
            @Override
            public void onTabChanged(String tabId) {
                viewPager.setCurrentItem(Integer.valueOf(tabId));
            }
        });

            viewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                super.onPageSelected(position);
                tabHost.setCurrentTab(position);
            }
        });
    }

    private class PageChangeListener implements ViewPager.OnPageChangeListener {
        private int scrollingState = ViewPager.SCROLL_STATE_IDLE;

        @Override
        public void onPageSelected(int position) {
            // スクロール中はonPageScrolled()で描画するのでここではしない
            if (scrollingState == ViewPager.SCROLL_STATE_IDLE) {
                updateIndicatorPosition(position, 0);
            }
            tabWidget.setCurrentTab(position);
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            scrollingState = state;
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            updateIndicatorPosition(position, positionOffset);
        }

        private void updateIndicatorPosition(int position, float positionOffset) {
            View tabView = tabWidget.getChildTabViewAt(position);
            int indicatorWidth = tabView.getWidth();
            int indicatorLeft = (int) ((position + positionOffset) * indicatorWidth);

            final FrameLayout.LayoutParams layoutParams = (FrameLayout.LayoutParams) indicator.getLayoutParams();
            layoutParams.width = indicatorWidth;
            layoutParams.setMargins(indicatorLeft, 0, 0, 0);
            indicator.setLayoutParams(layoutParams);
        }
    }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <TabHost
        android:id="@android:id/tabhost"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?android:attr/colorPrimary">

        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="0dp"
            android:layout_height="0dp" />
        <View
            android:id="@+id/indicator"
            android:layout_width="match_parent"
            android:layout_height="2dp"
            android:layout_gravity="bottom"
            android:background="?android:attr/colorControlActivated" />

    </TabHost>

    <android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</android.support.v4.view.ViewPager>
    </LinearLayout> 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp"
        android:text="Left Fragment" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp"
        android:text="Center Fragment" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp"
        android:text="Right Fragment" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="1"
    android:gravity="bottom|center_horizontal"
    android:paddingBottom="16dp"
    android:textColor="@color/tab_widget_text"
    android:textSize="14sp"
    tools:layout_width="match_parent"
    tools:text="group 1 ITEM TWO" />

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <selector xmlns:android="http://schemas.android.com/apk/res/android">
        <item android:color="#FFFFFFFF" android:state_selected="true" />
        <item android:color="#99FFFFFF" />
    </selector>
</selector>