Why is my pointer NULL

[Stephen Black]

I have been given this exercise to do as quoted
"Create and activity with two layouts . In one , implement a List fragment. when a user clicks an Item in the list Fragment , change the fragment displayed in the second layout."

public class Duo extends ListFragment
{
static String[] pieChoices;
	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
	{
		//My understanding is that if you inflate a view with an xml file of type ListView with an id of @id/android:list
		//Then the list object will be placed first into the view and the actual list items will populate the xml defined 
		//list selector sections with the xml definded list selector colour
		View v=inflater.inflate(R.layout.duo, container, false);
		return v;
	}

	@Override
	public void onActivityCreated(Bundle savedInstanceState)
	{
	super.onCreate(savedInstanceState);
	//get the Array
	Resources resources=getResources();
	pieChoices=resources.getStringArray(R.array.pie_array);
	//Create a list adapter
	ArrayAdapter<String> pieArrayAdapter = new ArrayAdapter<String>(this.getActivity(),android.R.layout.simple_list_item_1, pieChoices);
	setListAdapter(pieArrayAdapter);
	}
	
	//This is how we know when someone clicks on our list items
	@Override
	public void onListItemClick(ListView lv, View v, int position, long id)
	{
	//Now we make and show a toast so that we know which one the user has clicked on
	String servePie= String.format("one %s pie coming up", pieChoices[position]);
	Toast piToast=Toast.makeText(this.getActivity().getApplicationContext(), servePie,Toast.LENGTH_SHORT);
	piToast.show();
	//Change the second layout 
	TextView resultView= (TextView) v.findViewById(R.id.textViewChange);
	resultView.setText(servePie);
	}
}

but line 35 or most likely line 36 throws a Null pointer Exception
This makes me think that the TextView cannot be referenced because it is in another layout?
This then makes me wonder how I can reference the text view called textViewChange
This also makes me think that I should include a copy of the xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".Duo" >

    <TextView
        android:id="@+id/textViewCause"
        android:layout_width="328dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="0dp"
        android:text="@string/cause"
        android:background="#E0AEFC"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <LinearLayout
        android:id="@+id/cause"
        android:layout_width="328dp"
        android:layout_height="wrap_content"
        android:background="#78789A"
        android:orientation="vertical" >
       <ListView
        android:id="@id/android:list"
        android:layout_width="328dp"
        android:layout_height="wrap_content"
        android:divider="@drawable/divider"
        android:listSelector="@drawable/selector">          
    	</ListView>
    </LinearLayout>

    <TextView
        android:id="@+id/textViewEffect"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="0dp"
        android:text="@string/effect"
        android:background="#E0AEFC"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <LinearLayout
        android:id="@+id/effect"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#78789A"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/textViewChange"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dp"
            android:text="@string/result"
            android:textAppearance="?android:attr/textAppearanceLarge" />
    </LinearLayout>

</LinearLayout>

Thanks in advance