BLoC.dart

import 'dart:async';

import 'package:bloc/bloc.dart';
import 'package:equatable/equatable.dart';

part 'mybloc_event.dart';
part 'mybloc_state.dart';

class MyblocBloc extends Bloc<MyblocEvent, MyblocState> {
  @override
  MyblocState get initialState => MyblocInitial();

  @override
  Stream<MyblocState> mapEventToState(
    MyblocEvent event,
  ) async* {
    if (event is SubmitForm) {
      yield FormLoading();
      yield FormLoaded();
    } 
  }
}
  

event.dart

part of 'mybloc_bloc.dart';

abstract class MyblocEvent extends Equatable {
  const MyblocEvent();
}

class SubmitForm extends MyblocEvent {
  @override
  // TODO: implement props
  List<Object> get props => null;
}

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

import 'MyPage2.dart';
import 'bloc/mybloc_bloc.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyPage(),
    );
  }
}

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: BlocProvider<MyblocBloc>(
          child: BlocConsumer<MyblocBloc, MyblocState>(
            listener: (context, state) {
              Navigator.push(
                  context, MaterialPageRoute(builder: (context) => MyPage2()));
            },
            builder: (context, state) {
              if (state is MyblocInitial) {
                return buildInitialInput(context);
              } else if (state is FormLoading) {
                return loadingwidget();
              }
              return loadingwidget();
            },
          ),
          create: (BuildContext context) {
            return MyblocBloc();
          },
        ),
      ),
    );
  }

  Widget loadingwidget() {
    print("=================inside loading State==================");
    return Center(
      child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 100),
          child: CircularProgressIndicator()),
    );
  }
}

Widget buildInitialInput(BuildContext context) {
  return Column(
    children: <Widget>[
      SizedBox(height: 50),
      TextFormField(
        decoration: InputDecoration(
          labelText: "Name",
          hintStyle: TextStyle(
            color: Colors.grey,
            fontSize: 16.0,
          ),
        ),
      ),
      TextFormField(
        decoration: InputDecoration(
          labelText: "City",
          hintStyle: TextStyle(
            color: Colors.grey,
            fontSize: 16.0,
          ),
        ),
      ),
      SizedBox(height: 25),
      FlatButton(
        color: Colors.blueAccent,
        onPressed: () {
          BlocProvider.of<MyblocBloc>(context).add(SubmitForm());
        },
        child: const Text(
          'Submit',
          style: TextStyle(fontSize: 20, color: Colors.white),
        ),
        shape: new RoundedRectangleBorder(
            borderRadius: new BorderRadius.circular(7.5)),
      ),
    ],
  );
}

MyPage2.dart

import 'package:flutter/material.dart';

class MyPage2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Text("\n\n\n\t\t\tWelcome"),
       
    );
  }
}

State.dart

part of 'mybloc_bloc.dart';

abstract class MyblocState extends Equatable {
  const MyblocState();
}

class MyblocInitial extends MyblocState {
  List<Object> get props => [];
}

class FormLoading extends MyblocState {
  @override
  // TODO: implement props
  List<Object> get props => null;
}

class FormLoaded extends MyblocState {
  @override
  // TODO: implement props
  List<Object> get props => null;
}