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.

Any help would be appreciated. Thanks!

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();
}

}