Android - Problema con SurfaceView

holder.addCallback(new SurfaceHolder.Callback() {

    @Override

    public void surfaceCreated(SurfaceHolder surfaceHolder) {

        if (holder.getSurface().isValid()) {

            canvas = holder.lockCanvas();

            drawTablero(canvas);

            holder.unlockCanvasAndPost(canvas);

        }

    }

    @Override

    public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

    }

    @Override

    public void surfaceDestroyed(SurfaceHolder surfaceHolder) {

    }

});

@Override

public void run() {

    if (game == null) {

        return;

    }

    handler.postDelayed(this, 1000 / 15);

    this.invalidate();

    draw();

    game.physics();

    game.processInput();

    touches.clear();

}

protected void draw() {

    if (holder.getSurface().isValid()) {

        canvas = holder.lockCanvas();

        if (game == null) {

            holder.unlockCanvasAndPost(canvas);

            return;

        } else {

            game.draw(canvas);

            holder.unlockCanvasAndPost(canvas);

        }

    }

}