The AppBarDesign can't be assigned to the parameter type 'PreferredSizeWidget'

Question

Anyone please give some information why this is happening?

When I try to add a class AppBarDesign which implements appBar flutter is gi

Answer 1

helpful tips to implementing that without searching any other topics:

class ApplicationToolbar extends StatelessWidget with PreferredSizeWidget{
  @override
  Widget build(BuildContext context) {
    return AppBar( ... );
  }

  @override
  Size get preferredSize => Size.fromHeight(kToolbarHeight);
}