This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final)

Question

Getting the below issue, and not able to solve it, Can anyone help me in solving this.

This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final). dart(must_be_immutable)

Thanks.

Answer 1

This issue occurs when all the class variables are not declared as final. You can either make them final or for ignoring this warning you can add the following comment above the class declaration:

//ignore: must_be_immutable

Answer 2

All fields in a class extending StatelessWidget should be final.

From the documentations.

StatelessWidget class. A widget that does not require mutable state.

https://api.flutter.dev/flutter/widgets/StatelessWidget-class.html

Answer 3

Make sure that all your instances variable in class are marked as final and the object is also marked as final.

In class

class Items {
  final String title;
  final String author;
  final String event;
  final String img;
  Items({this.title, this.author, this.event, this.img});
}

Inside widget that you in,

 final Items item2 = new Items(
    title: "Country",
    author: "Balaji",
    event: "4 Items",
    img: "assets/panda.png",
  );

Answer 4

Use That way

   class Frog extends StatelessWidget {
      const Frog({
      Key key,
      this.color = const Color(0xFF2DBD3A),
      this.child,
   }) : super(key: key);

  final Color color;
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return Container(color: color, child: child);
  }
}

Answer 5

From flutter doc:

The following is a skeleton of a stateless widget subclass called GreenFrog. Normally, widgets have more constructor arguments, each of which corresponds to a final property.

Just like this

class IconContainer extends StatelessWidget {
final double size;
final Color color;
final IconData icon;
IconContainer(this.icon, {this.color=Colors.white, this.size=32});
Widget build(BuildContext context) {
 //TODO...
}