Problem with class declarations due to null-CodePudding

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?

CodePudding user response：

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

CodePudding user response：

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.

CodePudding user response：

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;
  }
}