How to extend a class in Dart/Flutter

I have class A:

class A{
    String title;
    String content;
    IconData iconData;
    Function onTab;
    A({this.title, this.content, this.iconData, this.onTab});
}

How can i create class B that extends class A with additional variable like following:

class B extends A{
    bool read;
    B({this.read});
}

Tried with this but not working

let o = new B(
          title: "New notification",
          iconData: Icons.notifications,
          content: "Lorem ipsum doro si maet 100",
          read: false,
          onTab: (context) => {

          });

Solution 1:

You have to define the constructor on the child class.

class B extends A {
  bool read;
  B({title, content, iconData, onTab, this.read}) : super(title: title, content: content, iconData: iconData, onTab: onTab);
}