How to change one currency textfield via another currency textfield in flutter?

Question

Can you tell me how I calculate my one currency via listen my another currency textfield?

Now Still I have a problem. whenever my text field is empty i got an exception like

Invalid radix-10 number (at character 1) 0.0 ^

or

Invalid number (at character 1)

^

How can I solve this? Help me out. please. Thanks in advance.

final silverCoinController = TextEditingController();
  final goldCoinController = TextEditingController();

int silver = 0;
  double gold = 0.0;
  _convertSilver() {
    setState(() {
       //define your own formula
      silverCoinController.text = (gold * 1000).toString();
      print(gold);
    });
  }

  _convertGold() {
    setState(() {
       //define your own formula
      goldCoinController.text = (silver / 1000).toString();
      print(silver);
    });
  }

  _silverValue() {
    silver = int.parse(silverCoinController.text);
  }

  _goldValue() {
    gold = double.parse(goldCoinController.text);
  }

@override
  void initState() {
    silverCoinController.addListener(_silverValue);
    goldCoinController.addListener(_goldValue);

    super.initState();
  }

@override
  void dispose() {
    silverCoinController.dispose();
    goldCoinController.dispose();
    super.dispose();
  }

. . .

Column(
 children: <Widget> [
  TextField(
   keyboardType: TextInputType.numberWithOptions(decimal: true)
   onChanged: (text) {
     _convertGold();
   },
   controller: silverCoinController,
  ),
  TextField(
   keyboardType: TextInputType.numberWithOptions(decimal: true)
   onChanged: (text) {
     _convertSilver();
   },
   controller: silverCoinController,
  ),
 ]
)

Answer 1

You can copy paste run full code below
Step 1: sliver use double
Step 2: Check isNotEmpty for TextEditingController and onChanged

_silverValue() {
if (silverCoinController.text.isNotEmpty) {
  silver = double.parse(silverCoinController.text);
 }
}
...
onChanged: (text) {
              if (text.isNotEmpty) {
                _convertGold();
              }
            }

Step 3: Two TextField use the same silverCoinController need to modify

working demo

full code

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final silverCoinController = TextEditingController();
  final goldCoinController = TextEditingController();

  double silver = 0.0;
  double gold = 0.0;

  _convertSilver() {
    setState(() {
      //define your own formula
      silverCoinController.text = (gold * 1000).toString();
      print(gold);
    });
  }

  _convertGold() {
    setState(() {
      //define your own formula
      goldCoinController.text = (silver / 1000).toString();
      print(silver);
    });
  }

  _silverValue() {
    if (silverCoinController.text.isNotEmpty) {
      silver = double.parse(silverCoinController.text);
    }
  }

  _goldValue() {
    if (goldCoinController.text.isNotEmpty) {
      gold = double.parse(goldCoinController.text);
    }
  }

  @override
  void initState() {
    silverCoinController.addListener(_silverValue);
    goldCoinController.addListener(_goldValue);

    super.initState();
  }

  @override
  void dispose() {
    silverCoinController.dispose();
    goldCoinController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(children: <Widget>[
          TextField(
            decoration: InputDecoration(
              border: OutlineInputBorder(),
              labelText: 'Sliver',
            ),
            keyboardType: TextInputType.numberWithOptions(decimal: true),
            onChanged: (text) {
              if (text.isNotEmpty) {
                _convertGold();
              }
            },
            controller: silverCoinController,
          ),
          TextField(
            decoration: InputDecoration(
              border: OutlineInputBorder(),
              labelText: 'Gold',
            ),
            keyboardType: TextInputType.numberWithOptions(decimal: true),
            onChanged: (text) {
              if (text.isNotEmpty) {
                _convertSilver();
              }
            },
            controller: goldCoinController,
          ),
        ]),
      ),
    );
  }
}