Focus Node Test

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(home: MyHomePage(),),);

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  static final FocusNode _focusNode = FocusNode();
  static final TextEditingController _controller = TextEditingController();
  void _requestNode()=>  FocusScope.of(context).requestFocus(_focusNode);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TextField(
              focusNode: _focusNode,
              controller: _controller,                    
           ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: ()=>_requestNode(),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), 
    );
  }
}