Question 302061 in Flutter Question posted in
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Flutter list getting sync between screens

I have a list on Screen A
I Navigate to Screen B passing list on Screen A and modify few fields in the list in Screen B

And I press back.
Then the Screen A list is also getting updated.

I need to prevent updating Screen A list unless I manually update the list in Screen A

I am using Navigator to navigate to Scree A

Navigator.push used to pass the Screen A list to Screen B

I modify Screen B list and click on back
Screen A list should not update.

class PayeeList {
  List<PayeeData>? data;
}


class PayeeData {
  int? id;
  PayeeAttributes? attributes;
}


class PayeeAttributes {
  num? amount;
  String? createdAt;
  String? updatedAt;
  User? user;
}

Initial list as follow with some data

 List<PayeeData>? data = [];




List<PayeeData> payees=  data.toList();
var result = await Navigator.push(context,
    MaterialPageRoute(builder: (context) => MultiBlocProvider(
         providers: [
              //REMOVED for sharing in stack overflow
         ],
         child: ExpensePayeesScreen(
             title: "Payees",
             isEdit: false,
             paidAmounts:payees,
              totalAmount: 100))),
          );

When I return from screen B the data list getting updated

———–SOLVED———–

I solved issue by creating the passing temp array as below

List<PayeeData> temp = [];
expenseData.attributes?.payees?.data?.forEach((element) {
      PayeeAttributes payeeAttributes = PayeeAttributes(amount: element.attributes?.amount ?? 0, user: element.attributes?.user ?? User());
      temp.add(PayeeData(id: element.id, attributes: payeeAttributes));
});
Tags:

2

Answers


  1. 0

    Call toList when passing the list to navigator

    This will create a new list with the same elements, which means updating the parent list won’t update the newly created one.

    void main() {
  final a = [1,2,3];
  final b = a;
  
  a.add(4);
  print('a: $a');         // a: [1, 2, 3, 4]
  print('b: $b');         // b: [1, 2, 3, 4]
  
  final c = a.toList();

  a.add(5);
  print('a: $a');         // a: [1, 2, 3, 4, 5]
  print('c: $c');         // c: [1, 2, 3, 4]
}

    You can also see other methods to create a new list in that manner here: How to copy list values to another list in flutter

    There’s also an explanation of why that happens in an answer in that question: https://stackoverflow.com/a/58389737/10210069

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  2. 0

    If you want to create a new list from reference from previous list,

    List<String> listA = ["apple", "banana", "cat"];

    Instead of directly assigning list like:

    List<String> listB = listA;

    You can do,

    List<String> listB = List.from(listA);

    This will create a completely new list from data of listA and modifying listB will not affect listA.

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