Sidescrolling Sprite in Android Studio

I want to create a simple sushi game where plates of sushi are moved on a platform in front of you (only in the horizontal direction; no vertical movement), and you have to collect certain plates of sushi for points. I'm new to game development.

This is what I currently have in Android Studio (took out irrelevant parts of the code). I can't figure out how to get the sushi images to scroll across the screen. I'm also very lost as to how I'm supposed to "tick" the game. I added a timer, but can't wrap my head around how to use it. Should I have a while loop somewhere that keeps updating the game as long as a boolean variable gameOver is false?

Currently, all I get when I run the app is the background image.

public class MainActivity extends ActionBarActivity {

    private static int highScore;
    private Canvas canvas = new Canvas();
    // View view = (View) findViewById(R.id.imageView);
    ImageView imageView;
    Timer timer;

    List<Sushi> sushis = new ArrayList<Sushi>();
    List<Integer> sushiImages = new ArrayList<Integer>();
    private static int points = 0;
    private boolean isGameOver = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageView = new ImageView(this);
        loadSushiImages();
        makeSushi();
        addTimer();
    }

    public void loadSushiImages() {
        sushiImages.add(R.drawable.ebi);
        sushiImages.add(R.drawable.anago);
    }

    public int getScreenWidth() {
        DisplayMetrics dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);
        return dm.widthPixels;
    }

    public void update() {
        moveSushis();
        imageView.invalidate();
        drawSushis();
    }

    public void moveSushis() {
        for (int i = 0; i < sushis.size(); i++) {
           Sushi s = sushis.get(i);
           s.move();
            if (s.getX() > getScreenWidth()) {
                sushis.remove(s);
                makeSushi();
            }
        }
    }

    public void drawSushis() {
        for (int i = 0; i < sushis.size(); i++) {
            Drawable icon = getResources().getDrawable(sushis.get(i).getPicNumber());
            icon.setBounds(
                    0 - icon.getIntrinsicWidth() / 2, 0 - icon.getIntrinsicHeight(),
                    icon.getIntrinsicWidth() / 2, 0);

            icon.draw(canvas);
        }
    }

    public void makeSushi() {
        Random r = new Random();
        int sushiNumber = sushiImages.get(r.nextInt(sushiImages.size() - 1));
        Sushi s = new Sushi(sushiNumber);
        sushis.add(s);

        Drawable icon = getResources().getDrawable(sushiNumber);

        icon.setBounds(
                0 - icon.getIntrinsicWidth() / 2, 0 - icon.getIntrinsicHeight(),
                icon.getIntrinsicWidth() / 2, 0);

        icon.draw(canvas);


        /* Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
        Canvas c = new Canvas(b); */
    }

    private void addTimer() {
        timer = new Timer(true);
        // update();
    }
}