MainActivity.java

    private void showShoppingListDialog() {

        MealIngredientContract mealIngredientContract = new MealIngredientContract();

        Dinner[] dinners = dinnerContract.getDinners(dbHelper);
        List<Meal> meals = new ArrayList<>();

        for (Dinner dinner : dinners) {
            Meal meal = dinner.getMeal();
            meals.add(meal);
        }

        AlertDialog d = new AlertDialog.Builder(this)
                .setTitle(R.string.shopping_list)
                .setPositiveButton(android.R.string.ok, null)
                .setMessage(mealIngredientContract.getShoppingList(meals, dbHelper))
                .create();
        d.show();
    }