Problem with class declarations due to null

user_13247321 0
Viewed 77

I've just updated Flutter and Dart and the following code no longer compiles. I understand it's to do with nulls, but not sure how to fix.

class DataCancelled {
  bool cancelledOK;

  DataCancelled({this.cancelledOK});

  DataCancelled.fromJson(Map<String, dynamic> json) {
    cancelledOK = json['value'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['value'] = this.cancelledOK;
    return data;
  }
}

The line "DataCancelled({this.cancelledOK});" has the following error: The parameter 'cancelledOK' can't have a value of 'null' because of its type, but the implicit default value is 'null'.

And the line "DataCancelled.fromJson(Map<String, dynamic> json) {" has the following error: Non-nullable instance field 'cancelledOK' must be initialized. (Documentation) Try adding an initializer expression, or add a field initializer in this constructor, or mark it 'late'.

What do I need to do to fix this?

dart flutter
3 Answers

Either make cancelledOK nullable like this bool? cancelledOk or make it required like this required this.cancelledOK

user_157477570

You either need to make cancelledOK optional by doing this :

bool? cancelledOK;

Or you need to add "required" keyword before this.cancelledOk in the constructor. This will solve your problem.

user_108065930

If your member is required:

class DataCancelled {
  late bool cancelledOK;

  DataCancelled({required this.cancelledOK});

  DataCancelled.fromJson(Map<String, dynamic> json) {
    cancelledOK = json['value'];
  }

  Map<String, dynamic> toJson() {
    final data = <String, dynamic>{};
    data['value'] = cancelledOK;
    return data;
  }
}

If it is indeed optional:

class DataCancelled {
  bool? cancelledOK;

  DataCancelled({this.cancelledOK});

  DataCancelled.fromJson(Map<String, dynamic> json) {
    cancelledOK = json['value'];
  }

  Map<String, dynamic> toJson() {
    final data = <String, dynamic>{};
    data['value'] = cancelledOK;
    return data;
  }
}
user_20607250
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