Flutter: How to update final int value in model?

Question

I have this model:

Class Model {
 Model({required this.title, required this.amount});

 final String title;
 final int amount;
}

User get to see this data and have an option to change the amount. When I try to change values of amount like this list[index].amount = 3 I got "'amount' can't be used as a setter because it's final. Try finding a different setter, or making 'amount' non-final" message. How can I update value of amount?

Right now I'm using this workaround:

for (final model in list) {
 if (model.title == _title) {
  list[list.indexOf(model)] = Model(
   title: model.title,
   amount: _selectedAmount;
  );
 }
}

So, basically reassign it.

Answer 1

You can use copyWith method to create new instance with updated value

class Model {
 const  Model({
    required this.title,
    required this.amount,
  });

  final String title;
  final int amount;

  Model copyWith({
    String? title,
    int? amount,
  }) {
    return Model(
      title: title ?? this.title,
      amount: amount ?? this.amount,
    );
  }
}

Now you can pass the filed you like to update like model.copyWith(amount: _selectedAmount);