home_veli_mixin.dart

import 'package:flutter/material.dart';
import 'package:vbaseproject/features/v2/demo/home_veli_view.dart';

mixin HomeVeliMixin on State<HomeVeliView> {
  void showErrorMessage();

  void fetchUserDeteail({required String id}) {
    const response = true;
    if (!response) return;
    showErrorMessage();
  }
}

home_veli_view.dart

import 'package:flutter/material.dart';
import 'package:vbaseproject/features/v2/demo/home_veli_mixin.dart';

class HomeVeliView extends StatefulWidget {
  const HomeVeliView({super.key});

  @override
  State<HomeVeliView> createState() => _HomeVeliViewState();
}

class _HomeVeliViewState extends State<HomeVeliView> with HomeVeliMixin {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: () => fetchUserDeteail(id: 'vb'),
      ),
      appBar: AppBar(
        title: const Text('Veli'),
      ),
      body: const Center(
        child: Text('Veli'),
      ),
    );
  }

  @override
  void showErrorMessage() {
    {
      showDialog<bool>(
        context: context,
        builder: (context) {
          return const Text('Olley hsogeldin');
        },
      );
    }
  }
}

This is a sample about delegation for flutter