textfield.dart

import 'package:flutter/material.dart';

class CampoTexto extends StatefulWidget {
  const CampoTexto({Key? key}) : super(key: key);

  @override
  State<CampoTexto> createState() => _CampoTextoState();
}

class _CampoTextoState extends State<CampoTexto> {

  TextEditingController _textEditingController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("I/O"),
        backgroundColor: Colors.deepPurple,
      ),
      backgroundColor: Colors.white,
      body: Column(
        children: [
          Padding(
            padding: EdgeInsets.all(32),
            child: TextField(
              keyboardType: TextInputType.number,
              decoration: InputDecoration(
                labelText: "Digite um valor"
              ),
              maxLength: 4,
              style: TextStyle(color: Colors.purple, fontSize: 30),
              controller: _textEditingController,
            ),
          ),
          ElevatedButton(onPressed: () {
            print("Value: ${_textEditingController.text}");
          }, child: Text("Save"))
        ],
      ),
    );
  }
}