我是Android的新手，我不明白为什么当我从一个活动发送数据到另一个活动时，它不记得我以前保存的值，并且它无法向我显示购物车中的多个项目。
范例：
我有购物单和推车单
在购物列表中，我有一个recycleview，当我按下添加按钮时，我可以将项目添加到购物车中，通过将数据发送到cart活动，将项目添加到购物车中，并且它显示recycle视图中的数据（此recycleview位于Cart活动中）但现在如果我回去使用手机的后退按钮，我从购物清单中选择另一个项目，当我去购物车列表前一个项目添加它's不见了，我不明白为什么，因为我创建了一个ArrayList，并将数据保存在其中。谁能告诉我我做错了什么？
我将添加3张照片来更好地解释自己。

的数据

的
在第二幅图中，如果我从购物车返回到购物列表并点击C，购物车中的A将消失，我将只有C。
下面是我的代码：

购物清单：

public class FirebaseSearch extends AppCompatActivity {

private EditText mSearchField;
private ImageButton mSearchBtn;
private ImageButton AddToCart;
private ImageButton Cart;

String searchText="";

private RecyclerView mResultList;
private DatabaseReference mUserDatabase;



private static ArrayList<Users> arrayList = new ArrayList<>();
public static int cart_count = 0;


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

    mUserDatabase = FirebaseDatabase.getInstance().getReference("Users");

    mSearchField = findViewById(R.id.search_field);
    mSearchBtn   = findViewById(R.id.search_btn);
    mResultList  = findViewById(R.id.result_list_cart);
    AddToCart    = findViewById(R.id.imageButton2);
    Cart         = findViewById(R.id.cartButton);

    mResultList.setHasFixedSize(true);
    mResultList.setLayoutManager(new LinearLayoutManager(this));

    mSearchBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            searchText = mSearchField.getText().toString();
            firebaseUserSearch(searchText);
        }
    });

    Cart.setOnClickListener(new View.OnClickListener() {
        private Object Tag="Activity";

        @Override
        public void onClick(View v) {
            if (cart_count < 1) {

            } else {
                startActivity(new Intent(FirebaseSearch.this, CartActivity.class));
            }
        }
    });
}


private void firebaseUserSearch(String searchText) {
    Toast.makeText(FirebaseSearch.this, "Started Search", Toast.LENGTH_LONG).show();
    Query firebaseSearchQuery = 
   mUserDatabase.orderByChild("Name").startAt(searchText).endAt(searchText + "\uf8ff");
    FirebaseRecyclerAdapter<Users, UsersViewHolder> firebaseRecyclerAdapter = new 
    FirebaseRecyclerAdapter<Users, UsersViewHolder>(
            Users.class,
            R.layout.list_layout,
            UsersViewHolder.class,
            firebaseSearchQuery
    ) {
        @Override
        protected void populateViewHolder(UsersViewHolder viewHolder, Users model, int position) {
            viewHolder.getDetails(model.getName(), model.getSurname(),model.getPrice());
            viewHolder.setDetails(model.getName(), model.getSurname(),model.getPrice());
        }
    };
    mResultList.setAdapter(firebaseRecyclerAdapter);
}

@Override
protected void onStart() {
    super.onStart();
    invalidateOptionsMenu();
}

// View Holder Class
public static class UsersViewHolder extends RecyclerView.ViewHolder {
    View mView;
    String nome;
    String surname;
    Long prezzo;
    public UsersViewHolder(View itemView) {
        super(itemView);
        mView = itemView;
        ImageButton addToCart = (ImageButton)mView.findViewById(R.id.imageButton2);
        addToCart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                cart_count++;
                Context context = v.getContext();
                Intent intent = new Intent(context, CartActivity.class);
                intent.putExtra("Name",nome);
                intent.putExtra("Surname",surname);
                intent.putExtra("Prezzo",Long.toString(prezzo));
                context.startActivity(intent);
            }
        });
    }

    public void getDetails(String name,String cognome,Long price){
        nome=name;
        surname=cognome;
        prezzo=price;
    }

    public void setDetails(String name, String surname, Long price) {

        TextView user_name = (TextView) mView.findViewById(R.id.name_text);
        TextView user_surname = (TextView)mView.findViewById(R.id.status_text);
        TextView user_price = (TextView)mView.findViewById(R.id.price);

        user_name.setText(name);
        user_surname.setText(surname);
        user_price.setText(Long.toString(price));

    }
}
}enter code here

字符串

购物车：

public class CartActivity extends AppCompatActivity {
private RecyclerView cities;
private RecyclerView.Adapter adapter;
String nome,cognome;
Long prezzo;
int totalPrice=0;
TextView campoPrezzo;
int position=0;

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

    campoPrezzo=findViewById(R.id.TotalPrice);

    //Receive the data from the previous activity
    String passedArg = getIntent().getExtras().getString("Name");
    nome=passedArg;
    String passedArg2 = getIntent().getExtras().getString("Surname");
    cognome=passedArg2;

    Intent intent = getIntent();
    String str = intent.getStringExtra("Prezzo");

    ArrayList<Users> cities = initCities(nome,cognome,Long. parseLong(str));

    this.cities = (RecyclerView) findViewById(R.id.cartList);
    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(this);
    this.cities.setLayoutManager(mLayoutManager);

    adapter = new ProductAdapter(cities);
    this.cities.setAdapter(adapter);
    System.out.println("Prezzo"+returnTotalPrice());
}

private ArrayList<Users> initCities(String nome,String cognome,Long price) {
    ArrayList<Users> list = new ArrayList<>();
    list.add(position,new Users(nome,cognome,price));
    position++;
    getTotalPrice(price);
    return list;
}

public void getTotalPrice(Long price){
    totalPrice+=price;
}

public int returnTotalPrice(){
    return totalPrice;
}
}

型