Ошибка при динамическом добавлении фрагментов -java.lang.IllegalStateException:

Я работаю над 3.0 впервые. Я хочу добавлять фрагменты динамически , , но показывала ошибку: -

10-18 18:29:11.215: ERROR/AndroidRuntime(3550): java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.

XML-код

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/frags">

<ListView
        android:id="@+id/number_list"
        android:layout_width="250dip"
        android:layout_height="match_parent" />

<FrameLayout
        android:id="@+id/the_frag"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

Activity

public class FragmentExampleActivity extends Activity implements
    OnItemClickListener {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    ListView l = (ListView) findViewById(R.id.number_list);
    ArrayAdapter<String> numbers = new ArrayAdapter<String>(
            getApplicationContext(), android.R.layout.simple_list_item_1,
            new String[] { "one", "two", "three", "four", "five", "six" });
    l.setAdapter(numbers);
    l.setOnItemClickListener(this);
}

public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

    Fragment f = new FragmentExample();

    FragmentTransaction ft = getFragmentManager().beginTransaction();       
    ft.replace(R.id.the_frag, f);
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    ft.addToBackStack(null);
    ft.commit();

}
}


public class FragmentExample extends Fragment {
private int nAndroids=1;

public FragmentExample() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle saved) {
    int n;

    View l = inflater.inflate(R.layout.textlay,container);
    TextView tv = (TextView) l.findViewById(R.id.textView1);
    tv.setText("value "+nAndroids);

    return l;
}

}

Просьба пролить свет, где я ошибаюсь: (