import 'package:flutter/material.dart';

import 'package:flutter_calculator/flutter_calculator.dart';

void main() => runApp(FlutterCalculatorExample());

class FlutterCalculatorExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // ...
      home: const HomePage(title: 'Flutter Calculator Example'),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final TextEditingController _textController = TextEditingController(text: '0.00');

  @override
  void dispose() {
    this._textController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // ...
      body: TextField(
        showCursor: false,
        readOnly: true,
        controller: this._textController,
        onTap: () => this._showCalculatorDialog(context),
      ),
    );
  }

  void _showCalculatorDialog(BuildContext context) async {
    final result = await showCalculator(context: this.context) ?? 0.00;

    this._textController.value = this._textController.value.copyWith(
          text: result.toStringAsFixed(2),
        );
  }
}