code_fixed_future_builder.dart

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:doctorradar/pages/doctorssubmit.dart';
import 'dart:async';

int i=1;
String name='2';
bool exist=false;
final Controller = TextEditingController();

class LoginPage extends StatefulWidget {
  static String tag = 'login-page';
  @override
  _LoginPageState createState() => new _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  @override
  void dispose() {
    // Clean up the controller when the Widget is disposed
    Controller.dispose();
    super.dispose();
  }

  Future<bool> doesNameAlreadyExist(String name) async {
  final QuerySnapshot result = await Firestore.instance
      .collection('IDS')
      .where('ID$i', isEqualTo: name)
      .limit(1)
      .getDocuments();
  final List<DocumentSnapshot> documents = result.documents;
  final result = documents.length == 1;
   setState(() {
                    exist=result;
                  });
    
  return result;
}




  @override
  Widget build(BuildContext context) {
    final logo = Hero(
      tag: 'hero',
      child: CircleAvatar(
        backgroundColor: Colors.transparent,
        radius: 48.0,
        child: Image.asset('lib/images/logo.png'),
      ),
    );

    final email = TextFormField(
      keyboardType: TextInputType.emailAddress,
      autofocus: false,
      decoration: InputDecoration(
        hintText: 'Your ID',
        contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
        border: OutlineInputBorder(borderRadius: BorderRadius.circular(32.0)),
      ),
      controller: Controller,
    );

    final loginButton = Padding(
      padding: EdgeInsets.symmetric(vertical: 16.0),
      child: Material(
        borderRadius: BorderRadius.circular(30.0),
        shadowColor: Colors.lightBlueAccent.shade100,
        elevation: 5.0,
        child: MaterialButton(
          minWidth: 200.0,
          height: 42.0,
          onPressed: () {
             setState(() {
               name=Controller.text;
             });
             if(exist==true){
               Navigator.push(
                 context,
                 MaterialPageRoute(
                     builder: (context) => Submit()),
               );

             } else if(exist==false){
               print("Wrong Credintials");
             }

          },
          color: Colors.lightBlueAccent,
          child: Text('Log In', style: TextStyle(color: Colors.white)),
        ),
      ),
    );

    return Scaffold(
      backgroundColor: Colors.white,
      body: Center(
        child: ListView(
          shrinkWrap: true,
          padding: EdgeInsets.only(left: 24.0, right: 24.0),
          children: <Widget>[
            logo,
            SizedBox(height: 48.0),
            email,
            SizedBox(height: 8.0),
            SizedBox(height: 24.0),
            loginButton,
            FutureBuilder(
              future: doesNameAlreadyExist(name),
              builder: (context, AsyncSnapshot<bool> result) {
                if (!result.hasData)
                  return Container(); // future still needs to be finished (loading)
                if (result.data){ // result.data is the returned bool from doesNameAlreadyExists               
                  return Text('A company called "Nova" already exists.');

                }
                else
                  return Text('Your ID does Not exist');
              },
            ),
          ],
        ),
      ),
    );
  }
}