Nifty control trouble

GameEngine.java

package org.caster.client;

import com.jme3.app.SimpleApplication;
import com.jme3.asset.plugins.FileLocator;
import com.jme3.niftygui.NiftyJmeDisplay;
import de.lessvoid.nifty.Nifty;
import de.lessvoid.nifty.controls.TextField;
import de.lessvoid.nifty.screen.Screen;
import de.lessvoid.nifty.screen.ScreenController;
import org.json.JSONObject;

import java.util.Queue;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Created by IntelliJ IDEA.
 * User: demoth
 * Date: 8/13/12
 * Time: 3:23 PM
 * <p/>
 * Draws the model and stores commands from user in 'out'
 */
public class GameEngine extends SimpleApplication {
    private Queue<JSONObject> out;
    private WorldModel model;

    Nifty nifty;
    private ScreenController controller;
    public GameEngine(Queue<JSONObject> out, WorldModel model) {
        this.out = out;
        this.model = model;
        this.controller = new ScreenController() {
            private Nifty nifty;

            public void login() {
                TextField loginField = this.nifty.getScreen("login").findNiftyControl("login_field", TextField.class);
                TextField passwordField = this.nifty.getScreen("login").findNiftyControl("password_field", TextField.class);
                System.out.println("login lols");
            }

            @Override
            public void bind(Nifty nifty, Screen screen) {
                this.nifty = nifty;
            }

            @Override
            public void onStartScreen() {
                //To change body of implemented methods use File | Settings | File Templates.
            }

            @Override
            public void onEndScreen() {
                //To change body of implemented methods use File | Settings | File Templates.
            }
        };

    }

    @Override
    public void simpleInitApp() {
        NiftyJmeDisplay niftyDisplay = new NiftyJmeDisplay(assetManager, inputManager, audioRenderer, guiViewPort);
        this.nifty = niftyDisplay.getNifty();
        assetManager.registerLocator("/media/f9157386-4243-4142-836c-e97e978bb8ba/media/devel/src/java/client/jCaster/res", FileLocator.class);

        nifty.fromXml("gui/gui.xml", "login", controller);
        guiViewPort.addProcessor(niftyDisplay);
        inputManager.setCursorVisible(true);
        flyCam.setEnabled(false);


    }


}

gui.xml

<?xml version="1.0" encoding="UTF-8"?>
<nifty xmlns="http://nifty-gui.sourceforge.net/nifty-1.3.xsd"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://nifty-gui.sourceforge.net/nifty-1.3.xsd http://nifty-gui.sourceforge.net/nifty-1.3.xsd">

    <useStyles filename="nifty-default-styles.xml"/>
    <useControls filename="nifty-default-controls.xml"/>

    <screen id="login">
        <layer id="login" childLayout="center">
            <panel childLayout="vertical" width="50%">
                <panel childLayout="horizontal">
                    <panel id="labels" childLayout="vertical" width="50%">
                        <control name="label" text="login"/>
                        <control name="label" text="password"/>
                        <control name="label" text="remember"/>
                    </panel>
                    <panel id="fields" childLayout="vertical" width="50%">
                        <control id="login_field" name="textfield" maxLength="20" text=""/>
                        <control id="password_field" name="textfield" maxLength="20" text="" passwordChar="*"/>
                        <control id="remember_field" name="checkbox"/>
                    </panel>
                </panel>
                <panel childLayout="horizontal">
                    <control id="login_button" name="button" label="login" visibleToMouse="true">
                        <interact onClick="login()"/>
                    </control>
                    <control id="cancel_button" name="button" label="cancel"/>
                </panel>
            </panel>


        </layer>
    </screen>


</nifty>