我在网上搜索了很多关于在一个操作栏标签中有多个片段的可能性。
This question最接近我的需要，但代码不起作用。
是否有其他可能性在一个选项卡中包含多个片段？
这是StartActivity

public class StartActivity extends FragmentActivity implements ActionBar.TabListener {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_start);

        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        actionBar.addTab(
              actionBar.newTab()
             .setText("Karte")
              .setTabListener(new MapFragmentListener(this)));

    }

对应的布局acticity_start包含用于将被放置在标签中的两个片段的两个帧布局。

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

    <FrameLayout
        android:id="@+id/fragment_map"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>
    <FrameLayout
        android:id="@+id/fragment_realtime"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

TabListener看起来像这样：

private class TabListener implements ActionBar.TabListener {

        private static final String fragment1_tag = "fragment1_tag";
        private static final String fragment2_tag = "fragment2_tag";

        private FragmentActivity activity;
        private RealtimeFragment fragment1;
        private RealtimeFragment fragment2;

        public TabListener(FragmentActivity activity) {

            this.activity = activity;

            android.support.v4.app.FragmentTransaction ft = activity.getSupportFragmentManager().beginTransaction();

            fragment1 = (RealtimeFragment) activity.getSupportFragmentManager().findFragmentByTag(fragment1_tag);
            if (fragment1 != null && !fragment1.isDetached()) {
                ft.detach(fragment1);
            }

            fragment2 = (RealtimeFragment) activity.getSupportFragmentManager().findFragmentByTag(fragment2_tag);
            if (fragment2 != null && !fragment2.isDetached()) {
                ft.detach(fragment2);
            }

            ft.commit();
        }

        @Override
        public void onTabReselected(Tab tab, FragmentTransaction ft) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onTabSelected(Tab tab, FragmentTransaction ft) {

            android.support.v4.app.FragmentTransaction fragmentTransaction = activity.getSupportFragmentManager().beginTransaction();

            if(fragment1 == null) {
                fragment1 = new RealtimeFragment();
                fragmentTransaction.add(R.id.fragment_map, fragment1, fragment1_tag);
            } else {
                fragmentTransaction.attach(fragment1);
            }

            if(fragment2 == null) {
                fragment2 = new RealtimeFragment();
                fragmentTransaction.add(R.id.fragment_realtime, fragment2, fragment2_tag);
            } else {
                fragmentTransaction.attach(fragment2);
            }

            fragmentTransaction.commit();

        }

        @Override
        public void onTabUnselected(Tab tab, FragmentTransaction ft) {

            android.support.v4.app.FragmentTransaction fragementTransaction = activity.getSupportFragmentManager().beginTransaction();

            if(fragment1_tag != null)
                fragementTransaction.detach(fragment1);
            if(fragment2 != null)
                fragementTransaction.detach(fragment2);

            fragementTransaction.commit();

        }

    }

类RealtimeFragment和相应的布局fragment_realtime如下所示：

public class RealtimeFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         View view = inflater.inflate(R.layout.fragment_realtime, container, false);
        return view;
    }
}

<?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" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

在一个选项卡中，现在应该显示RealtimeFragment类的两个片段。这些片段只显示一个按钮，但什么也没有显示！为什么？