title: TextFormField data disappear when closing the Key Board
body: <p>I am building a flutter app, and I have a <code>Register</code> form there. I am using <code>TextFormFields</code> and below is my code.</p>
  
  <pre><code>import 'package:flutter/material.dart';
  
  class RegisterPage extends StatelessWidget {
    final borderColorGreen = const Color(0xff339966);
  
    TextEditingController nameTxtController =TextEditingController();
    TextEditingController emailTxtController =TextEditingController();
    TextEditingController mobileTxtController =TextEditingController();
    TextEditingController passwordTxtController =TextEditingController();
    TextEditingController confirmPasswordTxtController =TextEditingController();
  
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        body: Container(
          decoration: BoxDecoration(
            image: DecorationImage(
              image: AssetImage("assets/images/background_login_5.jpg"),
              fit: BoxFit.cover,
            ),
          ),
          child: ListView(
            children: &lt;Widget&gt;[
              _buildTitleSection(),
              _buildInputFields("Name",nameTxtController),
              _buildInputFields("Email",emailTxtController),
              _buildInputFields("Mobile",mobileTxtController),
              _buildInputFields("Password",passwordTxtController),
              _buildInputFields("Confirm Password",confirmPasswordTxtController),
              _buildRegisterButton(),
            ],
          ),
        ),
      );
    }
  
    Widget _buildTitleSection() {
      return Container(
          margin: EdgeInsets.only(top: 40),
          padding: EdgeInsets.all(32),
          child: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: &lt;Widget&gt;[
              Text(
                "something.xyz",
                style: TextStyle(
                  color: borderColorGreen,
                  fontWeight: FontWeight.w900,
                  fontSize: 25,
                ),
              ),
            ],
          ));
    }
  
    Widget _buildInputFields(String label, TextEditingController textController) {
      return Container(
          margin: EdgeInsets.only(left: 20, bottom: 20),
          child: Column(
            children: &lt;Widget&gt;[
  
              Container(
                padding: EdgeInsets.only(right: 20),
                child: Row(
                  children: &lt;Widget&gt;[
                    Flexible(
                      child: TextFormField(
                        controller: textController,
                        style: new TextStyle(color: Colors.white),
                        decoration: InputDecoration(
                          labelText: label,
                          fillColor: Colors.white,
                          labelStyle: TextStyle(
                              color: Colors.white, fontWeight: FontWeight.w600),
                          enabledBorder: OutlineInputBorder(
                            borderSide: const BorderSide(
                                color: Colors.white30, width: 2.0),
                            borderRadius: BorderRadius.circular(25.0),
                          ),
                        ),
                      ),
                    ),
                  ],
                ),
              ),
            ],
          ));
    }
  
  
  
  
  
    Widget _buildRegisterButton() {
      return Container(
        margin: EdgeInsets.only(top: 10, right: 20, left: 20),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: &lt;Widget&gt;[
            Flexible(
                child: SizedBox(
                    width: double.infinity, // match_parent
                    child: RaisedButton(
                      child: Text(
                        "Create Account",
                        style: TextStyle(
                            color: Colors.white,
                            fontSize: 18,
                            fontWeight: FontWeight.normal),
                      ),
                      shape: RoundedRectangleBorder(
                          borderRadius: new BorderRadius.circular(30.0)),
                      color: borderColorGreen,
                      onPressed: () {},
                    )))
          ],
        ),
      );
    }
  
  
  }
  </code></pre>
  
  <p>When I click on a <code>TextField</code> the keyboard opens and I can type text. However if I press the <strong>back button</strong> of my phone to close the keyboard, then the text I entered  from all fields. 
  I am referring to the hardware back button available in Android phones. </p>
  
  <p>The form is scrllable and after entering text to a <code>TextField</code> if I clicked on the other <code>TextField</code>, the text stay there as it should. If I press the back button to close the keyboard, all text in the form is gone.</p>
  
  <p>How can I fix this issue?</p>