Android 3 - Add a Fragment programmatically: Illegal state exception

Question

I am trying to build an App which is swapping its fragments by interactions with its user. There is a Fragment defined in the Activity's XML and a LinearLayout which should contain another Fragment.

My main activity:

public class DashActivity extends Activity {
private static final String TAG = "DashActivity";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_dashboard);
    //-- Instantiate Fragmentstuff
    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    ActivitystreamFragment asf = new ActivitystreamFragment();

    fragmentTransaction.add(R.id.rightfrag, asf);
    fragmentTransaction.commit();
    Log.i(TAG, "RightView has been committed");
}

its XML file:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >
    <fragment
    android:id="@+id/fragment_dashboard"
        android:layout_width="5dp"
        android:layout_height="fill_parent"
        android:layout_marginLeft="20dp"
        android:layout_weight="0.97"
        android:name="de.upb.cs.ginkgo.tablet.ui.fragments.DashboardFragment" >
    <!-- Preview: layout=@layout/fragment_dashboard -->
        </fragment>
    <LinearLayout
        android:id="@+id/rightfrag"
        android:layout_width="450dp" 
        android:layout_height="match_parent"
        android:layout_weight="1" 
        android:layout_marginTop="10dp"
        android:layout_marginBottom="15dp"
        android:layout_marginRight="10dp" >
    </LinearLayout>
</LinearLayout>

My fragment:

public class ActivitystreamFragment extends ListFragment {
private static final String TAG = "ActivitystreamFragment";
ArrayList<Status> states;

 public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        Log.i(TAG,"Begin: Inflate");
        View root = inflater.inflate(R.layout.fragment_activitystream, container);
        Log.i(TAG,"Finished: Inflate");
        if(root == null)
            Log.e(TAG, "omg Inflate == null");
        return root;
        }

 @Override
 public void onCreate(Bundle savedInstanceState){
     super.onCreate(savedInstanceState);
     states = new ArrayList<Status>();
     // THE FOLLOWING HAS TO BE DELETED LATER!!
     Profile p1 = new Profile("1", null, "Max Muster", 
             null, null, null, null, null, null, null);
     Status status1 = new Status(p1,"Hello world", "12.02.2012", null);
     states.add(status1);
     // --- DELTE ----------------------------
     ActivitystreamAdapter asa = new ActivitystreamAdapter(getActivity(), R.layout.list_item_event, states);
     setListAdapter(asa);
     Log.i(TAG, "onCreate is done");

 }

}

Fragments XML:

<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"

        android:id="@+id/android:list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:drawSelectorOnTop="false"
        android:background="@drawable/back_rightfrag" >

</ListView>

And the output from Logcat:

01-25 14:14:29.788: I/Process(781): Sending signal. PID: 781 SIG: 9
01-25 14:17:32.387: I/DashActivity(814): RightView has been committed
01-25 14:17:32.387: I/ActivitystreamFragment(814): onCreate is done
01-25 14:17:32.397: I/ActivitystreamFragment(814): Begin: Inflate
01-25 14:17:32.467: D/dalvikvm(814): GC_FOR_ALLOC freed 86K, 3% free 6509K/6663K, paused 59ms
01-25 14:17:32.477: I/dalvikvm-heap(814): Grow heap (frag case) to 6.902MB for 513744-byte allocation
01-25 14:17:32.597: D/dalvikvm(814): GC_CONCURRENT freed 3K, 3% free 7007K/7175K, paused 4ms+4ms
01-25 14:17:32.657: I/ActivitystreamFragment(814): Finished: Inflate
01-25 14:17:32.657: D/AndroidRuntime(814): Shutting down VM
01-25 14:17:32.657: W/dalvikvm(814): threadid=1: thread exiting with uncaught exception (group=0x40014760)
01-25 14:17:32.677: E/AndroidRuntime(814): FATAL EXCEPTION: main
01-25 14:17:32.677: E/AndroidRuntime(814): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.upb.cs.ginkgo.tablet/de.upb.cs.ginkgo.tablet.ui.DashActivity}: java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1815)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.ActivityThread.access$500(ActivityThread.java:122)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.os.Looper.loop(Looper.java:132)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.ActivityThread.main(ActivityThread.java:4123)
01-25 14:17:32.677: E/AndroidRuntime(814):  at java.lang.reflect.Method.invokeNative(Native Method)
01-25 14:17:32.677: E/AndroidRuntime(814):  at java.lang.reflect.Method.invoke(Method.java:491)
01-25 14:17:32.677: E/AndroidRuntime(814):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
01-25 14:17:32.677: E/AndroidRuntime(814):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
01-25 14:17:32.677: E/AndroidRuntime(814):  at dalvik.system.NativeStart.main(Native Method)
01-25 14:17:32.677: E/AndroidRuntime(814): Caused by: java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.view.ViewGroup.addViewInner(ViewGroup.java:3011)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.view.ViewGroup.addView(ViewGroup.java:2900)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.view.ViewGroup.addView(ViewGroup.java:2857)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.view.ViewGroup.addView(ViewGroup.java:2837)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:787)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:977)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.BackStackRecord.run(BackStackRecord.java:638)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1309)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.Activity.performStart(Activity.java:4406)
01-25 14:17:32.677: E/AndroidRuntime(814):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1788)
01-25 14:17:32.677: E/AndroidRuntime(814):  ... 11 more

Answer 1

Change the line

View root = inflater.inflate(R.layout.fragment_activitystream, container);

to

View root = inflater.inflate(R.layout.fragment_activitystream, null);

or even better:

View root = inflater.inflate(R.layout.fragment_activitystream, container, false);

And it should work. Don't ask me why attaching the fragment to the container you want it to go in doesn't work, but it doesn't...