doctor_app_flutter/lib/screens/auth/login_screen.dart

import 'dart:async';

import 'package:doctor_app_flutter/lookups/auth_lookup.dart';
import 'package:doctor_app_flutter/util/dr_app_shared_pref.dart';
import 'package:doctor_app_flutter/widgets/auth/known_user_login.dart';
import 'package:doctor_app_flutter/widgets/shared/dr_app_circular_progress_Indeicator.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

import '../../widgets/auth/auth_header.dart';
import '../../widgets/auth/login_form.dart';

DrAppSharedPreferances SharedPref = new DrAppSharedPreferances();
class Loginsreen extends StatefulWidget {
  @override
  _LoginsreenState createState() => _LoginsreenState();
}


class _LoginsreenState extends State<Loginsreen> {
  Future<SharedPreferences> _prefs = SharedPreferences.getInstance();

  String platformImei;

  Future<String> platformImeiFuture;

  Future<void> getSharedPref() async {
    SharedPref.getString('platformImei').then((imei){
      platformImei = imei;
    });
  }

  @override
  void initState() {
    super.initState();
    platformImeiFuture = _prefs.then((SharedPreferences prefs) {
      return (prefs.getString('platformImei'));
    });
  }

  @override
  Widget build(BuildContext context) {
    getSharedPref();
    return Scaffold(
      backgroundColor: Colors.white,
      body: SingleChildScrollView(
        child: FutureBuilder(
            future: platformImeiFuture,
            builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
              switch (snapshot.connectionState) {
                case ConnectionState.waiting:
                  return DrAppCircularProgressIndeicator();
                default:
                  if (snapshot.hasError) {
                    return Text('Error: ${snapshot.error}');
                  } else {
                    return Container(
                        margin: EdgeInsetsDirectional.fromSTEB(30, 0, 0, 0),
                        alignment: Alignment.topLeft,
                        child: Column(
                            crossAxisAlignment: CrossAxisAlignment.start,
                            children: <Widget>[
                              (platformImei == null)
                                  ? Column(
                                      crossAxisAlignment:
                                          CrossAxisAlignment.start,
                                      children: <Widget>[
                                          AuthHeader(loginType.knownUser),
                                        LoginForm(),
                                      ],
                                    )
                                  : Column(
                                      crossAxisAlignment:
                                          CrossAxisAlignment.start,
                                      children: <Widget>[
                                        AuthHeader(loginType.unknownUser),
                                        KnownUserLogin(),
                                      ],
                                    ),
                            ]));
                  }
              }
            }),
      ),
    );
  }
}