exampleDialog.dart

import 'package:flutter/material.dart';

class Consts {
  Consts._();

  static const double padding = 16.0;
  static const double buttonPadding = 5.0;
}

class ExampleDialogText extends StatefulWidget {
  @override
  _ExampleDialogTextState createState() => _ExampleDialogTextState();
}

class _ExampleDialogTextState extends State<ExampleDialogText> {
  FocusNode focusNode = FocusNode();
  final textController = TextEditingController();
  bool noText = false;
  String nameList = "";

  @override
  void initState() {
    super.initState();
    nameList = "";
    focusNode.addListener(() {
      if (!focusNode.hasFocus) {
        setState(() {
          noText = nameList.length == 0;
        });
        FocusScope.of(context).requestFocus(focusNode);
      }
    });
  }

 

  @override
  Widget build(BuildContext context) {
    showDialogNameList() {
      return showDialog(
          context: context,
          builder: (context) {
            var screenHeight = MediaQuery.of(context).size.height;
            return Dialog(
                shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(Consts.padding),
                ),
                elevation: 0.0,
                child: Container(
                  height: screenHeight / 3,
                  child: Stack(
                    children: <Widget>[
                      Container(
                        padding: EdgeInsets.only(
                          top: Consts.padding,
                          bottom: Consts.padding,
                          left: Consts.padding,
                          right: Consts.padding,
                        ),
                        margin: EdgeInsets.only(top: 0),
                        decoration: BoxDecoration(
                          color: Colors.white,
                          shape: BoxShape.rectangle,
                          borderRadius: BorderRadius.circular(Consts.padding),
                          boxShadow: [
                            BoxShadow(
                              color: Colors.black26,
                              blurRadius: 10.0,
                              offset: const Offset(0.0, 10.0),
                            ),
                          ],
                        ),
                        child: Center(
                          child: Column(
                            mainAxisAlignment: MainAxisAlignment.spaceAround,
                            children: <Widget>[
                              TextField(
                                focusNode: focusNode,
                                autofocus: true,
                                controller: textController,
                                cursorColor: Colors.white,
                                style: TextStyle(
                                    color: Colors.black, fontSize: 14),
                                decoration: InputDecoration(
                                  counterText: '',
                                  errorText:
                                      noText ? 'Value Can\'t Be Empty' : null,
                                  hintText: 'List Name',
                                  enabledBorder: OutlineInputBorder(
                                    borderSide: BorderSide(color: Colors.black),
                                  ),
                                  focusedBorder: OutlineInputBorder(
                                    borderSide: BorderSide(color: Colors.green),
                                  ),
                                  labelStyle: TextStyle(
                                      color: Colors.white,
                                      fontWeight: FontWeight.bold),
                                ),
                                onChanged: (String text) {
                                  nameList = text;
                                },
                              ),
                              Padding(
                                padding: const EdgeInsets.all(8.0),
                                child: Row(
                                  crossAxisAlignment: CrossAxisAlignment.center,
                                  mainAxisAlignment: MainAxisAlignment.center,
                                  children: <Widget>[
                                    Container(
                                      width: 150.0,
                                      height: 45.0,
                                      child: RaisedButton(
                                        shape: RoundedRectangleBorder(
                                          borderRadius:
                                              BorderRadius.circular(10),
                                        ),
                                        onPressed: () {
                                          setState(() {
                                            nameList.isEmpty
                                                ? noText = true
                                                : noText = false;
                                          });
                                        },
                                        padding: EdgeInsets.fromLTRB(
                                            0.0, 0.0, 0.0, 0.0),
                                        color: Color(0xFF2DA771),
                                        child: Text('Add',
                                            style: TextStyle(
                                                color: Colors.white,
                                                fontFamily: 'Roboto',
                                                fontSize: 16)),
                                      ),
                                    ),
                                  ],
                                ),
                              )
                            ],
                          ),
                        ),
                      )
                    ],
                  ),
                ));
          });
    }

    return Scaffold(
      backgroundColor: Colors.blueAccent,
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          showDialogNameList();
        },
        backgroundColor: Colors.orange,
        child: Icon(
          Icons.add,
          color: Colors.purple,
          size: 40,
        ),
      ),
    );
  }
}