invalid_override_of_non_virtual_member

The member '{0}' is declared non-virtual in '{1}' and can't be overridden in subclasses.

The analyzer produces this diagnostic when a member of a class, mixin, or enum overrides a member that has the @nonVirtual annotation on it.

The following code produces this diagnostic because the method m in B overrides the method m in A, and the method m in A is annotated with the @nonVirtual annotation:

import 'package:meta/meta.dart';
​
class A {
  @nonVirtual
  void m() {}
}
​
class B extends A {
  @override
  void m() {}
}

If the annotation on the method in the superclass is correct (the method in the superclass is not intended to be overridden), then remove or rename the overriding method:

import 'package:meta/meta.dart';
​
class A {
  @nonVirtual
  void m() {}
}
​
class B extends A {}

If the method in the superclass is intended to be overridden, then remove the @nonVirtual annotation:

class A {
  void m() {}
}
​
class B extends A {
  @override
  void m() {}
}