Onpressed button UnActiveted ... ! plz give me any solution ..Thank you

i'm new to flutter and i'm tried many tym fr this api access and it is accessing but problem is that.. when i called onpress button Unactived... i pass parameter to textfileds and its passing....! actully can u check whre is the problm fr Unactivte button without SignUp function code read ??

look in the SignUp method in that method i describe to navigate when if my response is != null then i want navigate ! but in my case not happen in my code plz help me

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';
import 'package:sms_snd/data.dart';
import 'new.dart';



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

  class Loginpage extends StatefulWidget {
  @override
  _LoginpageState createState() => _LoginpageState();
   }

  class _LoginpageState extends State<Loginpage> {
  Signup(String email,String Password) async{
    SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
    Map data = {
       "APIKEY":"QVBAMTIjMllIRC1TREFTNUQtNUFTRksyMjE4Ng==",
       "SECRETKEY":"MjQ1QDEyIzJZSEQtODVEQTJTM0RFQTg1Mz1JRTVCNEE1ODY=",
       "Email": email,
       "Password":Password
   };
    var jsonResponse;
    var response = await http.post("http://services.edbrix.net/auth/login",
      headers: <String, String>{
        'Content-Type': 'application/json; charset=UTF-8',
      },
      body: jsonEncode(data));
    if (response.statusCode == 200){
      jsonResponse = json.decode(response.body);
      print("Response status : ${response.statusCode}");
      print("Response status : ${response.body}");
      if(jsonResponse != null){

        setState(() {
          _isLoading = false;
        });
        sharedPreferences.setString("AccessToken", jsonResponse["AccessToken"]);
        Navigator.of(context).pushAndRemoveUntil(MaterialPageRoute(builder: (BuildContext context) => 
    newapp()), (Route<dynamic> route) => false);
      }
      else{
        setState(() {
          _isLoading = false;
        });
        print("Response status : ${response.body}");
      }
      }
    }
   String _email;
   bool _isLoading = false;
   String _pass;
   final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
   final TextEditingController emailController = new TextEditingController();
  final TextEditingController passwordController = new TextEditingController();

   @override
   Widget build(BuildContext context) {
  return Scaffold(
  backgroundColor: Colors.white10,
  body:_isLoading ? Center(child: CircularProgressIndicator()) : Form(
    key: _formKey,
    child: Stack(
      children: <Widget>[
        Positioned(
          left: 40,
          right: 40,
          top: 250,
          child: Center(
            child: Text(
              'Welcome!',
              style: GoogleFonts.nunito(
                fontSize: 31,
                color: const Color(0xfff58634),
                fontWeight: FontWeight.w700,
                height: 1.1290322580645162,
              ),
              textAlign: TextAlign.center,
            ),
          ),
        ),
        Positioned(
          left: 30,
          right: 30,
          top: 320,
          child: SizedBox(
            height: 50,
            width: 170,
            child: TextFormField(
              controller: emailController,
              cursorColor: Colors.black,

              style: TextStyle(color: Colors.white70),
              decoration: InputDecoration(
                icon: Icon(Icons.email, color: Colors.white70),
                hintText: "Email",
                border: UnderlineInputBorder(borderSide: BorderSide(color: Colors.white70)),
                hintStyle: TextStyle(color: Colors.white70),
              ),
            ),
          ),
        ),
        Positioned(
          left: 30,
          right: 30,
          top: 380,
          child: SizedBox(
            height: 50,
            width: 170,
            child: TextFormField(
              controller: passwordController,
              cursorColor: Colors.black,

              style: TextStyle(color: Colors.white70),
              decoration: InputDecoration(
                icon: Icon(Icons.lock, color: Colors.white70),
                hintText: "Password",
                border: UnderlineInputBorder(borderSide: BorderSide(color: Colors.white70)),
                hintStyle: TextStyle(color: Colors.white70),
              ),
            ),
          ),
        ),
        Positioned(
          top: 460,
          right: 30,
          child:SizedBox(
            height: 45,
            child: RaisedButton(
              onPressed:
              emailController.text == "" || passwordController.text == "" ? null : () {

                Signup(emailController.text.toString(), passwordController.text.toString());
              },
              shape: new RoundedRectangleBorder(borderRadius: new BorderRadius.circular(5.0)),
              color: const Color(0xfff58634),
              child: Text(
                "SEND OTP",style:
              GoogleFonts.nunito( color: const Color(0xffffffff),
                  fontSize: 12
              ),
              ),
            ),
          ),
        )
        ],
       ),
       ),
      );
     }
     }