CopyWith doesn't change value if null is passed

[radoslawsobies]

example MyObject.copyWith(field1: null) this will not set field1 to null value, old value remains

[andrasferenczi]

The original idea was to have non-null values in the field. Do you have a suggestion for what the generated code might look like?

[dalewking]

There are a number of solutions discussed here.

The basic idea is provide some optional-like wrapper class that must be used for nullable properties. Alternatively, you could provide additional methods for each nullable field to set it to null.

So perhaps in the example in addition to the regular copy constructor you would have another method name copyWithField1Null().

[dalewking]

Or perhaps there are additional boolean parameters to the copyWith like field1Null for each nullable field that says to interpret null as truly null.

So for example:

class Foo {
  final String? name;
}

Would generate a copy constructor like this:

  Foo copyWith({
    String? name,
    bool nameNull = false,
  }) {
    return Foo(
      name: name ?? (nameNull ? null : this.name),
    );
  }

[ricardoemerson]

A good solution for this is use ValueGetter like the sample bellow:

class ScheduleState {
  final ScheduleStatus status;
  final int? scheduleHour;
  final DateTime? scheduleDate;

  ScheduleState({required this.status, this.scheduleHour, this.scheduleDate});

  ScheduleState copyWith({
    ScheduleStatus? status,
    ValueGetter<int?>? scheduleHour,
    ValueGetter<DateTime?>? scheduleDate,
  }) {
    return ScheduleState(
      status: status ?? this.status,
      scheduleHour: scheduleHour != null ? scheduleHour() : this.scheduleHour,
      scheduleDate: scheduleDate != null ? scheduleDate() : this.scheduleDate,
    );
  }

And in controller to set values to nullable properties you must made a function call.

void selectHour(int hour) {
    if (hour == state.scheduleHour) {
      state = state.copyWith(scheduleHour: () => null);
    } else {
      state = state.copyWith(scheduleHour: () => hour);
    }
  }