how to fix the position of the elements when is appeared keyboard in flutter code example

Example 1: how textfield move up when keyboard appears flutter

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Animation Demo',
      theme: new ThemeData(
        primaryColor: new Color(0xFFFF0000),
      ),
      home: new FormDemo(),
    );
  }
}

class FormDemo extends StatefulWidget {
  @override
  _FormDemoState createState() => _FormDemoState();
}

class _FormDemoState extends State<FormDemo> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  Animation _animation;

  FocusNode _focusNode = FocusNode();

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(vsync: this, duration: Duration(milliseconds: 300));
    _animation = Tween(begin: 300.0, end: 50.0).animate(_controller)
    ..addListener(() {
      setState(() {});
    });

    _focusNode.addListener(() {
      if (_focusNode.hasFocus) {
        _controller.forward();
      } else {
        _controller.reverse();
      }
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    _focusNode.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomPadding: false, // this avoids the overflow error
      appBar: AppBar(
        title: Text('TextField Animation Demo'),
      ),
      body: new InkWell( // to dismiss the keyboard when the user tabs out of the TextField
        splashColor: Colors.transparent,
        onTap: () {
          FocusScope.of(context).requestFocus(FocusNode());
        },
        child: Container(
          padding: const EdgeInsets.all(20.0),
          child: Column(
            children: <Widget>[
              SizedBox(height: _animation.value),
              TextFormField(
                decoration: InputDecoration(
                  labelText: 'I move!',
                ),
                focusNode: _focusNode,
              )
            ],
          ),
        ),
      ),
    );
  }
}

Example 2: adjust keybaord behaviour in textform field flutter

var _ageController = TextEditingController();var _heightController = TextEditingController();var _weightController = TextEditingController();final FocusNode _ageFocus = FocusNode();  final FocusNode _heightFocus = FocusNode();  final FocusNode _weightFocus = FocusNode();var _mainPartView = Container(  width: 380.0,  height: 240.0,  color: Colors.grey,  child: Column(    children: <Widget>[      TextFormField(        controller: _ageController,        keyboardType: TextInputType.number,        textInputAction: TextInputAction.next,        focusNode: _ageFocus,        onFieldSubmitted: (term){          _fieldFocusChange(context, _ageFocus, _heightFocus);        },        decoration: InputDecoration(          labelText: 'Age',          hintText: 'Age',          icon: Icon(Icons.person_outline),          fillColor: Colors.white,        ),      ),      TextFormField(        controller: _heightController,        keyboardType: TextInputType.number,        textInputAction: TextInputAction.next,        focusNode: _heightFocus,        onFieldSubmitted: (term) {          _fieldFocusChange(context, _heightFocus, _weightFocus);        },        decoration: InputDecoration(            labelText: _heightMessage,            hintText: _heightMessage,            icon: Icon(Icons.assessment),            fillColor: Colors.white,        ),      ),      TextFormField(        controller: _weightController,        keyboardType: TextInputType.number,        textInputAction: TextInputAction.done,        focusNode: _weightFocus,        onFieldSubmitted: (value){          _weightFocus.unfocus();          _calculator();        },        decoration: InputDecoration(            labelText: _weightMessage,            hintText: _weightMessage,            icon: Icon(Icons.menu),            fillColor: Colors.white        ),      ),      Padding(padding: EdgeInsets.all(4.5)),      Center(        child: RaisedButton(          onPressed: _calculator,          color: Colors.pinkAccent,          child: Text(            'Calculate',            style: TextStyle(fontSize: 16.9),          ),          textColor: Colors.white70,        ),      )    ],  ),);_fieldFocusChange(BuildContext context, FocusNode currentFocus,FocusNode nextFocus) {    currentFocus.unfocus();    FocusScope.of(context).requestFocus(nextFocus);  }