poppupWindow & ListView : nullpointerexcepcion

[jediap]

Pequeño proyecto para realizar el funcionamiento correcto antes de meterlo
en la aplicación gorda, bueno:
Al pulsar un botón o un item del menú me salga un layoutinflater y dentro de ese layoutinflater se muestra una lista simple.

Me muestra el poppupwindow correctamente pero no el listview y me da error en: vlista.setAdapter(adaptador) con el error java.lang.nullpointerexception.
Espero que me podáis ayudar y muchas gracias pase lo que pase. Un saludo

Pego aquí el código.

Activity_main.xml

Código HTML:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="@string/hello_world" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/textView1"
        android:layout_below="@+id/textView1"
        android:layout_marginTop="28dp"
        android:text="Button" />

</RelativeLayout> 

inflater.xml

Código HTML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/screen"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#444444"
    android:gravity="center_horizontal|top"
    android:orientation="vertical" >

    <ListView
        android:id="@+id/listView1"
        android:layout_width="298dp"
        android:layout_height="match_parent" >
	</ListView>

</LinearLayout> 

MainActivity.class

Código:

package com.example.layoutinflater;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.PopupWindow;

public class MainActivity extends Activity implements OnClickListener {

	private Button boton;
	private ListView vLista;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		boton = (Button) findViewById(R.id.button1);
		boton.setOnClickListener(this);
		

	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}

	@Override
	public void onClick(View v) {
		switch (v.getId()) {
		case R.id.button1:
			initiatePopupWindow();
			break;

		default:
			break;
		}

	}

	private PopupWindow pw;

	private void initiatePopupWindow() {
		String[] l = { "hola", "hola", "hola", "hola", "hola", "hola", "hola",
				"hola", "hola", "hola", "hola" };
		try {
			// We need to get the instance of the LayoutInflater, use the
			// context of this activity
			LayoutInflater inflater = (LayoutInflater) MainActivity.this
					.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
			// Inflate the view from a predefined XML layout
			View layout = inflater.inflate(R.layout.inflater,
					(ViewGroup) findViewById(R.id.screen));
			// create a 300px width and 470px height PopupWindow
			pw = new PopupWindow(layout, 300, 470, true);
			// display the popup in the center
			pw.showAtLocation(layout, Gravity.CENTER, 0, 0);
			ArrayAdapter<String> adaptador = new ArrayAdapter<String>(this.getApplicationContext(),
					android.R.layout.simple_list_item_1, l);
			vLista = (ListView) findViewById(R.id.listView1);
			vLista.setAdapter(adaptador);
		} catch (Exception e) {
			e.printStackTrace();
		}

	}
}

e.prinstacke(ERROR)

01-16 02:37:51.339: W/System.err(5500): java.lang.NullPointerException
01-16 02:37:51.339: W/System.err(5500): at com.example.layoutinflater.MainActivity.initiatePo pupWindow(MainActivity.java:70)
01-16 02:37:51.339: W/System.err(5500): at com.example.layoutinflater.MainActivity.onClick(Ma inActivity.java:42)
01-16 02:37:51.339: W/System.err(5500): at android.view.View.performClick(View.java:3534)
01-16 02:37:51.339: W/System.err(5500): at android.view.View$PerformClick.run(View.java:14263 )
01-16 02:37:51.339: W/System.err(5500): at android.os.Handler.handleCallback(Handler.java:605 )
01-16 02:37:51.339: W/System.err(5500): at android.os.Handler.dispatchMessage(Handler.java:92 )
01-16 02:37:51.339: W/System.err(5500): at android.os.Looper.loop(Looper.java:137)
01-16 02:37:51.339: W/System.err(5500): at android.app.ActivityThread.main(ActivityThread.jav a:4441)
01-16 02:37:51.339: W/System.err(5500): at java.lang.reflect.Method.invokeNative(Native Method)
01-16 02:37:51.339: W/System.err(5500): at java.lang.reflect.Method.invoke(Method.java:511)
01-16 02:37:51.339: W/System.err(5500): at com.android.internal.os.ZygoteInit$MethodAndArgsCa ller.run(ZygoteInit.java:784)
01-16 02:37:51.339: W/System.err(5500): at com.android.internal.os.ZygoteInit.main(ZygoteInit .java:551)
01-16 02:37:51.339: W/System.err(5500): at dalvik.system.NativeStart.main(Native Method)