Un Explainable NullPointerException

[rooossone]

hey guys n gals,

Im having a problem with a new menu approach i found on the net here the link to the blog its on.

basically i have a canvas that paints seperate 'screens'. the splash screen works fine but when i come to the menu screen i get the exception. however, the screen is still painted and i just cant see why this exception is produced

The canvas class:

    protected void paint(Graphics g) 
    {
        if(GameStatus.SplashScreen)
            {
                this.splashScr.drawObject(g);
            }
            else if(GameStatus.Menu)
            {
                try
                {
                this.menuScr.drawObject(g); // THIS IS THE LINE CAUSING THE PROBLEM
                }
                catch(NullPointerException e)
                {
                    e.printStackTrace();
                }
            }
    }

The 'Screen' class is question:

public void drawObject(Graphics g) 
    {
        g.drawImage(bgImg, 0, 0, 0);
        g.setFont(Font.getFont(Font.FACE_SYSTEM, Font.STYLE_PLAIN, Font.SIZE_SMALL));
        
        String[] menuItems = 
        {
            MenuItems.NEW_GAME,
            MenuItems.OPTIONS,
            MenuItems.HELP,
            MenuItems.ABOUT,
            MenuItems.EXIT
        };
        
        for(int i = 0; i < menuItems.length; i++)
        {
            g.setColor(255, 255, 255);
            if(i == menuIndex)
            {
                g.setColor(255, 0, 0);
            }
            g.drawString(menuItems[i], 80, 130 + (i * 20), 0);
        }
    }

[jappit]

Hi rooossone,

have you checked if your menuScr variable is correctly initialized (so it is not null)?

Pit

[rooossone]

yeah its deffinately initialised because i can see that it has painted everything to the screen, the exception jumps up after everything has been painted, if also put in System.out's before and after every step in that method and i get the exception before i get any of the System.outs

public void drawObject(Graphics g) 
    {
        g.drawImage(bgImg, 0, 0, 0);
        System.out.println("bg painted fine");
        g.setFont(Font.getFont(Font.FACE_SYSTEM, Font.STYLE_PLAIN, Font.SIZE_SMALL));
        System.out.println("font set");
        String[] menuItems = 
        {
            MenuItems.NEW_GAME,
            MenuItems.OPTIONS,
            MenuItems.HELP,
            MenuItems.ABOUT,
            MenuItems.EXIT
        };
        System.out.println("array set");
        for(int i = 0; i < menuItems.length; i++)
        {
            System.out.println("element " + i);
            g.setColor(255, 255, 255);
            System.out.println("element color set");
            if(i == menuIndex)
            {
                System.out.println("menu index element set");
                g.setColor(255, 0, 0);
                System.out.println("selected color set");
            }
            System.out.println("element " + i + "prepare");
            g.drawString(menuItems[i], 80, 130 + (i * 20), 0);
            System.out.println("element " + i + "success");
        }
        System.out.println("loop finished");
    }

ive also printed out the ref var menuScr and i can see that it's not null (MenuPackage.MenuScreen@84aee8b)

[rooossone]

Hey Guys Im Still Having the same problem with my code and i could really do with a fresh set of eyes to see where i've gone wrong... I've uploaded my netbeans project for anyone to download and have a look at, any possible resolutions would be great!

My Netbeans Project

Thanks in advance

[ayushv2005]

hi,

i faced the same exception problem while changing displayables on S40 devices. the same code worked fine on all other platforms ... but not on S40. i had even posted a thread to this regard on this forum ... dont have the exact link at the moment but you can search for "NullPointerException while changing displayables" along with my ID. have a look at that and see if the solution helps.
i use a different mechanism for changing displayables - to change from Canvas1 to Canvas2, Canvas1 calls a method in the main midlet. that way all the changing of displayables is "centrally controlled" so to speak.
check out a few points:
1) is there any string item in your menu screen that might not have been initialised, but is being drawn?
2) ditto for image items
3) try putting a Thread.Sleep() call at the point just before you paint the menu screen. (as i've mentioned in my other thread) ... this would allow any thread running in the splashscreen to terminate properly

the Thread.Sleep() worked fine for me and since then i've not encountered this problem. however as i said, my technique for changing displayables is quite different from the approach you have used. incidentally, i noticed another aspect when i had faced the error - the exception is thrown only when you change between two Canvas classes ... the approach worked fine when i switched from the Canvas to a form class.

~ayush

Hey Guys Im Still Having the same problem with my code and i could really do with a fresh set of eyes to see where i've gone wrong... I've uploaded my netbeans project for anyone to download and have a look at, any possible resolutions would be great!

My Netbeans Project

Thanks in advance

[rooossone]

Hey I managed to sort that problem out by putting the menuScr initialisation in the canvas constructor. not ideal but it works. now i have a problem when closing and re-opening the app within the emulator. when i close it i set the bgImg in menuScr to null, set the game loop boolean to false and call notifyDestroyed() but when i goto re-open the app i get a null pointer exception for bgImg even though i intialise it in the menuScr constructor so why is it saying its null?