Question

I’m starting out with AndEngine (GLES2) and I’m trying to make a simple paddle Sprite and it’s connected body move when the TouchScreen is used. However, no matter how I tweak the code, it always returns a NullPointerException when I try to make a call on the body in question, no matter what the call happens to be.

Here’s my code for the creating the Paddle:

// Create the Paddle, body for said paddle, and register with the PhysicsWorld
    final FixtureDef objectFixtureDef = PhysicsFactory.createFixtureDef(1, 0.5f, 0.5f);    
    paddleSprite = new Paddle(mPaddle, getVertexBufferObjectManager());
    Body paddleBody = PhysicsFactory.createBoxBody(mPhysicsWorld, paddleSprite, BodyType.DynamicBody, objectFixtureDef);
    mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(paddleSprite, paddleBody, true, false));
    paddleBody.setUserData("Paddle");

// .... other Code for initializing sprites ..... //
    mScene.attachChild(paddleSprite);
    mScene.registerTouchArea(paddleSprite);
    mScene.setTouchAreaBindingOnActionDownEnabled(true);


// Method for TouchScreenInteraction
public boolean onSceneTouchEvent(Scene pScene, TouchEvent pSceneTouchEvent) {
    if(this.mPhysicsWorld != null){
    paddleBody.setTransform(new Vector2((pSceneTouchEvent.getX() - paddleSprite.getWidth() / 2)/PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT,
            (pSceneTouchEvent.getY() - paddleSprite.getHeight() / 2)/PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT),
            0);
    return true;
    }
return false;
}

paddleSprite, paddleBody, and physicsWorld are global objects so access is not an issue.

The NullPointerException occurs the moment I touch the screen. If I remove the offending function call, it works, for after a bit of touching it occasionally breaks the game. Besides this problem, the Box2D engine runs smoothly and another dynamic object (a small ball) interacts with the paddle just fine.

I can post the rest of the code if the problem can’t be determined from this, but I’ve been stuck on this for a week and I’d really appreciate some help so I can actually get started with project.

Thank you very much in advance!

Answer 1

This line right here is your problem. You’re creating a new, locally scoped paddleBody.

Body paddleBody = PhysicsFactory.createBoxBody(...);

When you try to use it for the touch event, you’re using a class level paddleBody which probably hasn’t been initialized at all. Just remove the Body from the offending line to avoid creating a new object:

paddleBody = PhysicsFactory.createBoxBody(...);