Create Add Card Payment UI In Flutter

main.dart

import 'package:flutter/material.dart';
import 'package:square_in_app_payments/models.dart';
import 'package:square_in_app_payments/in_app_payments.dart';

/** square_in_app_payments: ^1.5.1  -- Dependency want to add
 * and wamt to register (https://developer.squareup.com/us/en) this site*/
main(){
  runApp(MyApp());
}
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: AddCard(),
    );
  }
}

class AddCard extends StatefulWidget {
  @override
  _AddCardState createState() => _AddCardState();
}

class _AddCardState extends State<AddCard> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Card Payment"),
      ),
      body: Center(
        child: Text("Helllo World!"),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(
          Icons.credit_card
        ),
        onPressed: payWithCreditCard,
        tooltip: "AddCard",
      ),
    );
  }

  void payWithCreditCard() {
      InAppPayments.setSquareApplicationId('sq0idb-jo6LF54kwFrkgUK6-ytFUQ');
      InAppPayments.startCardEntryFlow(
        onCardNonceRequestSuccess: _success,
        onCardEntryCancel: _entryCancel,
      );
  }

  void _success(CardDetails result) {
    InAppPayments.completeCardEntry(
      onCardEntryComplete: _cardEntryComplete
    );
  }

  void _entryCancel() {
    print("Cansel");
  }

  void _cardEntryComplete() {
  }
}