Question

I’ve been following a tutorial here.

So far i have a Gameview and a Gameloop (a thread) set up alright but i just modified the run() method in my thread and i get this error in logcat:

• ERROR/AndroidRuntime(296): java.lang.NullPointerException
• ERROR/AndroidRuntime(296): at biz.hireholly.tutorial.GameLoop.run(GameLoop.java:76)

Which i’m guessing means line 76 is the problem?

that’s: canvas = this.surfaceHolder.lockCanvas();

I’ve commented this in my code snippet below:

@Override
public void run()
{
    Canvas canvas;
    Log.d(TAG, "Starting Game Loop");
    while (running) {
        canvas = null;
        //try locking canvas, so only we can edit pixels on surface
        try{
            canvas = this.surfaceHolder.lockCanvas(); //LINE 76
            synchronized (surfaceHolder){ 
                this.gameView.onDraw(canvas);
            }
        } finally{
            //in case of exception, 
            //surface is not left in an inconsistent state
            if (canvas != null){
                surfaceHolder.unlockCanvasAndPost(canvas);
            }
        }
    }
}

See the whole GameLoop class code here: http://pastebin.com/kfTy9vzY

Andd you can see my GameView class here: http://pastebin.com/BkmnrUPU

(They’re both pretty short)

I’ve been trying to figure it out for myself a few days now with google and just general fiddling but I’ve been unable too, i would very much appreciate anyone’s thoughts on the matter!

Answer 1

The problem is with your constructor in GameLoop.java. The line this.surfaceHolder = surfaceHolder;
should be this.surfaceHolder = surfaceholder; Note the capital ‘H’ in your original code.

If you’re using an IDE, you would’ve seen a warning such as “The assignment to variable surfaceHolder has no effect” on that line.