SEHR Basic actionbarsherlock tabs mit Fragmenten: FragmentTransaction null, in der onTabSelected () - Methode

Ich bin Implementierung von code aus einem Beispiel (http://arvid-g.de/12/android-4-actionbar-with-tabs-example) und versuchen, Sie zu konvertieren, um die Arbeit mit ActionBarSherlock.

Hier TabActivity.java:

package com.pnet;

import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.ActionBar.Tab;
import com.actionbarsherlock.app.SherlockActivity;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.util.Log;
import android.widget.Toast;

public class TabActivity extends SherlockActivity {

    private static String TAG = "TabActivity";
    public static Context appContext;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tab_activity);

       //ActionBar gets initiated
        ActionBar actionbar = getSupportActionBar();
      //Tell the ActionBar we want to use Tabs.
        actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
      //initiating both tabs and set text to it.
        ActionBar.Tab PlayerTab = actionbar.newTab().setText("Fragment A");
        ActionBar.Tab StationsTab = actionbar.newTab().setText("Fragment B");

     //create the two fragments we want to use for display content
        Fragment PlayerFragment = new AFragment();
        Fragment StationsFragment = new BFragment();

    //set the Tab listener. Now we can listen for clicks.
        PlayerTab.setTabListener(new MyTabsListener(PlayerFragment));
        StationsTab.setTabListener(new MyTabsListener(StationsFragment));

   //add the two tabs to the actionbar
        actionbar.addTab(PlayerTab);
        actionbar.addTab(StationsTab);
    }

    class MyTabsListener implements ActionBar.TabListener {
        public Fragment fragment;

        public MyTabsListener(Fragment fragment) {
        this.fragment = fragment;
        }

        @Override
        public void onTabSelected(Tab tab, FragmentTransaction ft) {
            //TODO Auto-generated method stub
            if (fragment == null) {
                Log.v(TAG, "fragment is null");
            }

            if (ft == null) {
                Log.v(TAG, "fragment TRANSACTION is null");
            }

            ft.replace(R.id.fragment_container, fragment);          
        }

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

        }

        @Override
        public void onTabReselected(Tab tab, FragmentTransaction ft) {
            //TODO Auto-generated method stub
            Toast.makeText(TabActivity.appContext, "Reselected!", Toast.LENGTH_LONG).show();

        }

    }
}

Hier AFragment.java

package com.pnet;

import com.actionbarsherlock.app.SherlockFragment;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class AFragment extends SherlockFragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        //Inflate the layout for this fragment
        return inflater.inflate(R.layout.afragment, container, false);
    }

}

Hier BFragment.java

package com.pnet;

import com.actionbarsherlock.app.SherlockFragment;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class BFragment extends SherlockFragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        //Inflate the layout for this fragment
        return inflater.inflate(R.layout.bfragment, container, false);
    }

}

Hier tab_activity.xml:

<LinearLayout android:layout_gravity="center" android:layout_height="fill_parent" android:layout_width="fill_parent" android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android">
<LinearLayout android:id="@+id/fragment_container" android:layout_height="match_parent" android:layout_width="match_parent">

 </LinearLayout>
</LinearLayout>

Hier afragment.xml:

<?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 xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:gravity="center_vertical|center_horizontal"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="@string/hello_world"/>


</LinearLayout>

Hier bfragment.xml

<?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 xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:gravity="center_vertical|center_horizontal"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="@string/tab_navigation_content"/>


</LinearLayout>

Wenn die Aktivität lädt es löst die onTabSelected() Methode. Ich legte ein paar if-Anweisungen überprüfen der Objekte für null, die in das Protokoll schreiben, und es zeigt, dass die FragmentTransaction-Objekt null ist. Jeder sehen, wohin ich gehe falsch gemacht? Danke.