flutter : concert class not called in abstract class has a static method

Static methods cannot be overridden in Dart. See this issue.

Instead do something like:

abstract class PostEditorInterface {
  List<String>? f();
}

class PostEditorImpl extends PostEditorInterface {
  @override
  List<String>? f() { return ['hi']; }
}

// ...

final PostEditorInterface postEditor = PostEditorImpl();

final list = postEditor.f();

An example with two packages:

// package A
abstract class PostEditorInterface {
  List<String>? f();
}

void methodA(PostEditorInterface postEditor) {
  // no access to Impl, no problem. We have the interface.
  print(postEditor.f()); // prints the list
}

// package B
import 'package A'; // let's say this works!

class PostEditorImpl extends PostEditorInterface {
  @override
  List<String>? f() { return ['hi']; }
}

// now use methodA as usual since here you have access to Impl

methodA(PostEditorImpl()); // it's going to print the list ['hi']