App is null when calling AppState method from Nifty

Troubleshooting gui
1

Hello. I’ve created an appstate - MenuState - and I believe it’s been initialised correctly. However, when I call a method from an associated Nifty screen, it throws a null exception when accessing the App.

Here’s how the app state is created in Main:

[java]

NiftyJmeDisplay niftyDisplay = new NiftyJmeDisplay(assetManager, inputManager, audioRenderer, guiViewPort);

guiViewPort.addProcessor(niftyDisplay);

nifty = niftyDisplay.getNifty();

menuState = new MenuState();
stateManager.attach(menuState);
nifty.addXml(“Interface/Screens/start.xml”);
menuState.setEnabled(false);[/java]

Here’s how it’s initialised (I’ve just included initialize() and bind()):

[java]
public SimpleApplication app;
private Nifty nifty;
private Screen screen;

@Override
public void initialize(AppStateManager stateManager, Application app) {
super.initialize(stateManager, app);
this.app = (SimpleApplication)app;
}

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

And when I call this MenuState function via a Nifty onClick interaction:

[java]
public void niftyMethod() {System.out.println("App ref: " + this.app); }
[/java]

I get “App ref: null”.

Have I created the app state correctly, and if so, how do I get access to the App?

EDIT:

I fixed it by altering my simpleInitApp() method thus:

[java]

NiftyJmeDisplay niftyDisplay = new NiftyJmeDisplay(assetManager, inputManager, audioRenderer, guiViewPort);

nifty = niftyDisplay.getNifty();
nifty.addXml("Interface/Screens/start.xml");
nifty.addXml("Interface/Screens/game.xml");
	
menuState = (MenuState) nifty.getScreen("start").getScreenController();
stateManager.attach(menuState);
	
gameState = (GameState) nifty.getScreen("game").getScreenController();
stateManager.attach(gameState);
	
nifty.gotoScreen("start");
menuState.setEnabled(true);
	
guiViewPort.addProcessor(niftyDisplay);

[/java]

I assume this is the recommended way to register screen controllers when working with AbstractAppStates and individual Nifty XML files?

2

Actually, I’m still confused, unfortunately.

In my GameState class I have a method called startNew(), which loads the scene, objects, lights, fog etc. When switching to gameState to start a new game from the main menu, it works fine.

Often, I like to skip the menu and just load the gameState straight up. But when I call startNew(), I get a null exception when trying to access the app variable, which I though was set during the initialize() method when the screen controller was attached?

This was added to my simpleInitApp() from the post above:

[java]
if (skipMenu)
{
nifty.gotoScreen(“game”);
menuState.setEnabled(false);
gameState.setEnabled(true);
gameState.startNew();
}
else
{
nifty.gotoScreen(“start”);
menuState.setEnabled(true);
gameState.setEnabled(false);
}
[/java]

I’d be grateful for any help here. Thanks.

3

I can’t see why your way wouldn’t work with a quick scan through - however it’s not the recommended way anyway.

Create the screen controllers yourself and attach them as app states, then use nifty.registerScreenControllers before calling the addXml.

4

Fantastic, that did it. Thanks very much.

I’ve been a bit confused about when to call things and how Initialize() was used. Manually building, attaching and registering the controllers sorted everything out.

5

Yes, that’s how I always do it just because it means I have control over what’s going on rather than relying on anything else.