使用drawImage时（与Slick2d一起使用）NullPointerException

Question

Have a bit of basic code put into the beginning of a game and have run into a bit of a hang with this nasty NullPointerException for no apparent reason.

Loader.java (main class)

public class Loader extends StateBasedGame {
public static final int menu = 0;
public static final int ingame = 1;

public Loader() {
    super("insertGameName");
    this.addState(new Menu(menu));
    this.addState(new Ingame(ingame));

}

public static void main(String args[]) throws SlickException {

    AppGameContainer gameContainer = new AppGameContainer(new Loader());
    gameContainer.setDisplayMode(rpg.Settings.WIDTH, rpg.Settings.HEIGHT, false);
    gameContainer.setVSync(true);
    try {
        gameContainer.start();
    } catch (SlickException e) {
        e.printStackTrace();
    }
}

public void initStatesList(GameContainer arg0) throws SlickException {
    this.getState(0).init(arg0, this);
    // this.getState(1).init(arg0, this);
    this.enterState(menu);
}

}

and Menu.java (Initial game state)

public class Menu extends BasicGameState {
Image logo;

public Menu(int menu) {
}

public void init(GameContainer arg0, StateBasedGame arg1) throws SlickException {
    logo = new Image("res/logo.png");
}

public void render(GameContainer arg0, StateBasedGame arg1, Graphics g) throws SlickException {
    g.setBackground(Color.red);
    g.drawImage(logo, 0, 0);
}

public void update(GameContainer arg0, StateBasedGame arg1, int arg2) throws SlickException {

}

public int getID() {

    return 0;
}

}

The NullPointerException is at Menu.java:23 (g.drawImage(logo, 0, 0); I was under the impression that all of this code had been done correctly, so it surprised me when I found out otherwise.

Side note: When fiddling with the code a bit, I found that changing 'logo' in g.drawImage(logo,0,0) for 'newImage("res/logo.png")' stopped the NullPointerException, but doesn't show the image, only the blank red background.

Answer 1

your method

render(GameContainer arg0, StateBasedGame arg1, Graphics g)

is not getting any Graphics object, that's why it is giving NullPointException when you are calling any method over g because the variable it is assigned a null value.

find out where this method is called and see if the arguments passed are correct.