Keyboard freeze issue.

sample.dart

import 'package:flutter/material.dart';

class AliceExample extends StatefulWidget {
  @override
  _AliceExampleState createState() => _AliceExampleState();
}

class _AliceExampleState extends State<AliceExample> {
  TextEditingController _textController;
  FocusNode focusNode;

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

    _textController = TextEditingController();
    focusNode = FocusNode();
  }

  _onTextChanged() {
    _textController.text = "";
  }

  @override
  Widget build(BuildContext context) {
    print("Restarted");
    // var cursorPos = new TextSelection.fromPosition(new TextPosition(offset: 0));
    // _textController.selection = cursorPos;

    _textController.addListener(_onTextChanged);

    return Scaffold(
      appBar: AppBar(
        title: Text("Network Tool"),
      ),
      body: SingleChildScrollView(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            crossAxisAlignment: CrossAxisAlignment.center,
            children: <Widget>[
              TextField(
                maxLength: 2,
                controller: _textController,
                onChanged: (String str) {
                  focusNode.unfocus();
                },
                focusNode: focusNode,
              )
            ],
          ),
        ),
      ),
    );
  }
}