Android : ViewPage Fragment disappear when reload again

The following is layout

test.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="match_parent"
          android:layout_height="match_parent">

<Button android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:text="Click"
        android:id="@+id/button"
        />

<!-- Framelayout to display Fragments -->
<FrameLayout
        android:id="@+id/frame_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

test_detail.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="match_parent"
          android:layout_height="match_parent">

<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Hello"
        android:id="@+id/textView" android:layout_gravity="center_horizontal"/>
</LinearLayout>

The following is my Activity code

    public class TestFragmentActivity extends FragmentActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.setContentView(R.layout.test);

    Button button = (Button) this.findViewById(R.id.button);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.frame_container, new HomeFragment()).commit();

        }
    });

    }

    public class HomeFragment extends Fragment {
    private PagerAdapter _adapter;

    public HomeFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.common_view_pager_layout, container, false);

        this._adapter = new PagerAdapter(TestFragmentActivity.this);
        this._adapter.add(new DetailFragment());

        ViewPager pager = (ViewPager) view.findViewById(R.id.MainViewerPage);
        pager.setAdapter(this._adapter);

        return view;
    }
    }


    public class DetailFragment extends Fragment {

    public DetailFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.test_detail, container, false);

        return rootView;
    }
    }


    public class PagerAdapter extends FragmentPagerAdapter {
    private ArrayList<Fragment> _fragments;

    public PagerAdapter(FragmentActivity activity) {
        super(activity.getSupportFragmentManager());

        this._fragments = new ArrayList<Fragment>();
    }

    public void add(Fragment fragment) {
        this._fragments.add(fragment);
    }

    @Override
    public Fragment getItem(int position) {
        return this._fragments.get(position);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return "Test";
    }

    @Override
    public int getCount() {
        return 1;
    }


    }
}

When I click a button the fragment in ViewPager was display

But when I click the button again the fragment disappear

Please help me.