Как быстро интегрировать Систему быстрых платежей (СБП) в приложение на Flutter

/** SbpPayPlugin */
class SbpPayPlugin : FlutterPlugin, MethodCallHandler, ActivityAware {

  private lateinit var channel: MethodChannel
  private lateinit var context: Context
  private var activity: Activity? = null

  companion object {
    @JvmStatic
    fun registerWith(registrar: PluginRegistry.Registrar) {
      val channel = MethodChannel(registrar.messenger(), "sbp_pay")
      channel.setMethodCallHandler(SbpPayPlugin())
    }
  }

  override fun onAttachedToEngine(@NonNull flutterPluginBinding:
FlutterPlugin.FlutterPluginBinding) {
    channel = MethodChannel(flutterPluginBinding.binaryMessenger, "sbp_pay")
    channel.setMethodCallHandler(this)
    context = flutterPluginBinding.applicationContext
  }

  override fun onMethodCall(@NonNull call: MethodCall, @NonNull result:    Result) {
    when (call.method) {
      "init" -> {
        // Инициализация SDK
        SBP.init(context)
        result.success(true)
      }

      "showPaymentModal" -> {
        // СБП с версии 1.2 использует не Activity, а FragmentManager
        val fragmentManager = (activity as FlutterFragmentActivity).supportFragmentManager
        try {
          SBP.showBankSelectorBottomSheetDialog(fragmentManager,
               call.arguments as String?
          )
          result.success(true)
        } catch (e: Exception) {
          // Перехват ошибок плагина
          result.error("-", e.localizedMessage, e.message)
        }
      }

      else -> result.notImplemented()
    }
  }

  override fun onDetachedFromEngine(@NonNull binding:
FlutterPlugin.FlutterPluginBinding) {
    channel.setMethodCallHandler(null)
  }

  override fun onAttachedToActivity(binding: ActivityPluginBinding) {
    activity = binding.activity
  }

  override fun onReattachedToActivityForConfigChanges(binding:
ActivityPluginBinding) {
    activity = binding.activity
  }

  override fun onDetachedFromActivityForConfigChanges() {
    activity = null
  }

  override fun onDetachedFromActivity() {
    activity = null
  }
}

import Flutter
import UIKit
import SBPWidget

public class SbpPayPlugin: NSObject, FlutterPlugin {

  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(name: "sbp_pay", binaryMessenger:
registrar.messenger())
    let instance = SbpPayPlugin()
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    switch call.method {
      // Запрашиваем при инициализации доступность SDK на iOS
      case "init":
        if #available(iOS 13.0, *) {
          result(true)
        } else {
          result(false)
        }
      case "showPaymentModal":
        if #available(iOS 13.0, *) {
          if let topController = getTopViewController() {
            do {
              try SBPWidgetSDK.shared.presentBankListViewController(paymentURL: call.arguments
as! String, parentViewController: topController)
               result(true)
           } catch (e) {
             result(FlutterError(code: "PluginError", message: error.localizedDescription, details: nil)) // Перехват ошибок плагина
           }
         } else {
           result(FlutterError(code: "PluginError", message: "SBP: Failed to implement controller", details: nil))
         }
       } else {
         result(false))
       }

     default:
      result(FlutterMethodNotImplemented)
    }
  }

  private func getTopViewController() -> UIViewController? {
    if var topController = UIApplication.shared.keyWindow?.rootViewController {
      while let presentedViewController = topController.presentedViewController {
        topController = presentedViewController
      }
      return topController
    }
    return nil
  }
}

import 'package:flutter/services.dart';

class SbpPay {
 static const MethodChannel _channel = MethodChannel('sbp_pay');

 static bool _wasInitialized = false;

 /// Флаг доступности [SbpPay] на данном устройстве.
 ///
 /// Доступен только после успешного [init], иначе ошибка.
 static bool get isAvailable => _isAvailable;
 static late bool _isAvailable;

 /// Инициализация плагина SbpPay.
 ///
 /// Возвращает false, если сервис не поддерживается устройством.
 static Future<bool> init() async {
   if (!_wasInitialized) {
     _isAvailable = await _channel
         .invokeMethod<bool?>('init')
         .then((value) => value ?? false);

     _wasInitialized = true;
     return _isAvailable;
   }

   return _isAvailable;
 }

 /// Вызов нативного окна SbpPay выбора банков.
 static Future<void> showPaymentModal(String link) {
   return _channel.invokeMethod('showPaymentModal', link);
 }
}

import 'package:flutter/material.dart';
import 'package:sbp_pay/sbp_pay.dart';


void main() => runApp(const MyApp());


class MyApp extends StatelessWidget {
 const MyApp({super.key});


 // Только ссылки такого формата позволяют открыть модалку, иначе падает исключение
 static const _paymentLink =
     'https://qr.nspk.ru/AS100001ORTF4GAF80KPJ53K186D9A3G?type=01&bank=100000000007&crc=0C8A';


 @override
 Widget build(BuildContext context) {
   return MaterialApp(
     home: Scaffold(
       appBar: AppBar(
         title: const Text('Plugin example app'),
       ),
       body: Builder(
         builder: (context) {
           return Center(
             child: TextButton(
               onPressed: () async {
                 final messenger = ScaffoldMessenger.of(context);
                 if (await SbpPay.init()) {
                   await SbpPay.showPaymentModal(_paymentLink);
                 } else {
                   messenger.showSnackBar(
                     const SnackBar(content: Text('Not supported')),
                   );
                 }
               },
               child: const Text('Running on'),
             ),
           );
         }
       ),
     ),
   );
 }
}