制作购物应用程序，但主要活动中的购物车计数不会转移到详细信息活动页面

Question

在我的应用中，显示的购物车数量不会从mainactivity转移到detailsactivity。例如，如果我添加3个项目，并且在mainactivity页面的购物车上的textview中显示3，则当我转到详细信息页面时，textview变为0。已经有几天了，需要帮助。谢谢。

在第二次活动中调用onCreateOptionsMenu将textview再次设置为0时出现问题

public class MenuActivity extends AppCompatActivity {
public static TextView tv;
public static List<GeneralFood> cartFoods = new ArrayList<>();
public Toolbar toolbar;


@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    return true;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);
    if (tv == null) {
        MenuItem item = menu.findItem(R.id.action_addcart);
        MenuItemCompat.setActionView(item, R.layout.cart_count_layout);
        RelativeLayout notifCount = (RelativeLayout) MenuItemCompat.getActionView(item);
        tv = notifCount.findViewById(R.id.hotlist_hot);
        View view = notifCount.findViewById(R.id.hotlist_bell);

        cartUpdate();

        view.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent myIntent = new Intent(MenuActivity.this, CartActivity.class);
                startActivity(myIntent);

            }
        });

    }else {
        cartUpdate();
    }
    return true;
}

public static void cartUpdate() {
    if (tv != null && cartFoods != null)
        tv.setText(Integer.toString(cartFoods.size()));
}

@Override
protected void onResume() {
    super.onResume();
    cartUpdate();
}

}

详细信息：

public class Details extends MenuActivity {


TextView foodTitle, foodPrice, foodCalories, foodDescription, foodFat, foodSodium, foodProtein;
ImageView foodImage;
ImageButton foodDetailsPlus;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_details);
    toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    getSupportActionBar().setTitle("Details");
    toolbar.setTitleTextColor(0xFFFFFFFF);
    toolbar.setNavigationIcon(R.drawable.ic_arrow_back_black_24dp);

    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Details.super.onBackPressed();
        }
    });


    foodTitle = findViewById(R.id.food_title);
    foodPrice = findViewById(R.id.food_price);
    foodCalories = findViewById(R.id.food_calories);
    foodDescription = findViewById(R.id.food_description);
    foodFat = findViewById(R.id.food_fat);
    foodSodium = findViewById(R.id.food_sodium);
    foodProtein = findViewById(R.id.food_protein);
    foodImage = findViewById(R.id.food_image);
    foodDetailsPlus = findViewById(R.id.regular_food_plus_details);

    foodTitle.setText(getIntent().getStringExtra("foodTitle"));
    foodPrice.setText(Double.toString(getIntent().getDoubleExtra("foodPrice", 0)));
    foodCalories.setText(Integer.toString(getIntent().getIntExtra("foodCalories", 0)));
    foodDescription.setText(getIntent().getStringExtra("foodDescription"));
    Picasso.get().load(getIntent().getStringExtra("foodImage")).fit().into(foodImage);
    foodFat.setText(Integer.toString(getIntent().getIntExtra("foodFat", 0)));
    foodSodium.setText(Integer.toString(getIntent().getIntExtra("foodSodium", 0)));
    foodProtein.setText(Integer.toString(getIntent().getIntExtra("foodProtein", 0)));

}

}

MainActivity：

public class MainActivity extends MenuActivity {

RecyclerView recyclerViewHorizontal;
RecyclerView recyclerViewVertical;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    getSupportActionBar().setTitle("Foodish");
    toolbar.setTitleTextColor(0xFFFFFFFF);

    recyclerViewHorizontal = findViewById(R.id.horizontal_recyclerview);
    LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
    recyclerViewHorizontal.setLayoutManager(linearLayoutManager);

    recyclerViewVertical = findViewById(R.id.vertical_recyclerview);
    LinearLayoutManager linearLayoutManager2 = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
    recyclerViewVertical.setLayoutManager(linearLayoutManager2);

    RetrofitInterface retrofitService = RetrofitClient.getClient().create(RetrofitInterface.class);

    Call<Food> call = retrofitService.getFoods();
    call.enqueue(new Callback<Food>() {
        @Override
        public void onResponse(Call<Food> call, Response<Food> response) {
            List<GeneralFood> popularFoods = response.body().getPopularFood();
            recyclerViewHorizontal.setAdapter(new HorizontalAdapter(popularFoods, R.layout.recyclerview_horizontal, MainActivity.this));

            List<GeneralFood> regularFoods = response.body().getRegularFood();
            recyclerViewVertical.setNestedScrollingEnabled(false);
            recyclerViewVertical.setAdapter(new VerticalAdapter(regularFoods, R.layout.recyclerview_vertical, getApplicationContext()));
        }

        @Override
        public void onFailure(Call<Food> call, Throwable t) {

        }
    });
}

}