json serialization with inheritance in dart - json

Question

I am using json annotation package to generate the json serialization boilerplate code. I have Base class
#JsonSerializable()
class UIWidget {
double? size = 50;
List<UIWidget> children = List.empty(growable: true);
factory UIWidget.fromJson(Map<String, dynamic> json) => _$UIWidgetFromJson(json);
Map<String, dynamic> toJson() => _$UIWidgetToJson(this);
}
I have several subclasses and one such is given below.
#JsonSerializable(explicitToJson: true)
class UIGridView extends UIWidget {
int scrollDirection = Axis.vertical.index;
String _showAxis = "Vertical";
int crossAxisCount = 3;
double mainAxisSpacing = 0.0;
double crossAxisSpacing = 0.0;
double childAspectRatio = 1.0;
factory UIGridView.fromJson(Map<String, dynamic> json) => _$UIGridViewFromJson(json);
Map<String, dynamic> toJson() => _$UIGridViewToJson(this);
}
If you notice, the UIWidget class has children property, which can contain any of the sub classes. The problem arise when I tried to generate the code. The fromJson method is generated as follows
..children = (json['children'] as List<dynamic>)
.map((e) => UIWidget.fromJson(e as Map<String, dynamic>))
.toList();
However, I needed to call the subclass fromjson and create instance of subclass. Is there a way to do this?

Answer 1

Where's your super() constructor? If you're extending UIWidget, you need to pass your params from the extending class to the parent class, and codegen will work as expected.
// Base class
#JsonSerializable()
class ParentClass {
final String? someString;
const ParentClass({
this.someString,
});
factory ParentClass.fromJson(Map<String, dynamic> json) =>
_$ParentClassFromJson(json);
Map<String, String> toJson() => Map.from(_$ParentClassToJson(this));
}
// Child class extending base
#JsonSerializable()
class ChildClass extends ParentClass {
final List<int> exampleList;
const ChildClass({
required this.exampleList,
String? someString,
}) : super(someString: someString);
factory ChildClass.fromJson(Map<String, dynamic> json) =>
_$ChildClassFromJson(json);
Map<String, String> toJson() =>
Map.from(_$ChildClassToJson(this));
}