main.dart file:



import 'package:flutter/material.dart';
import 'dropDowns.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: PreferredSize(
        child: Text("my app"),
        preferredSize: Size.fromHeight(55.0),
      ),
      body: Container(
        width: MediaQuery.of(context).size.width,
        child: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              DropDown(),
              Button(),
              // Row(
              //   mainAxisAlignment: MainAxisAlignment.spaceBetween,
              //   children: <Widget>[
              //     // Expanded(child: VahaPilota()),
              //     SizedBox(
              //       width: MediaQuery.of(context).size.width * 0.1,
              //     ),
              //     // DeleteBtn(),
              //   ],
              // ),
              // TextVahy(visibility: false),
            ],
          ),
        ),
      ),
    );
  }
}







DropDown.dart file:




import 'package:flutter/material.dart';

class DropDown extends StatefulWidget {
  @override
  DropDownState createState() => DropDownState();
}

class DropDownState extends State<DropDown> {
  List<String> _myList = ["Item 1", "Item 2", "Item 3", "Item 4"];

  var currentItemSelected = "Item 1";

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        color: Colors.blue,
        child: ButtonTheme(
          child: DropdownButton<String>(
            dropdownColor: Colors.blue,
            items: _myList.map((String dropDownStringItem) {
              return DropdownMenuItem<String>(
                value: dropDownStringItem,
                child: Text(
                  dropDownStringItem,
                ),
              );
            }).toList(),
            onChanged: (String newItemSelected) {
              setState(() {
                currentItemSelected = newItemSelected;
                Button(myText: newItemSelected);
              });
            },
            value: currentItemSelected,
          ),
        ),
      ),
    );
  }
}

class Button extends StatefulWidget {
  final String myText;
  Button({this.myText});

  @override
  ButtonState createState() => ButtonState();
}

class ButtonState extends State<Button> {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: <Widget>[
          RaisedButton(
            child: Text("Button"),
            onPressed: () {
              // it should update my 'myText' in Text widget below
            },
          ),
          Text(widget.myText == null ? "Default text" : widget.myText),
        ],
      ),
    );
  }
}