Expose userDefaults in Purchases.configure just like iOS repo

[om-ha]

Problem

The original problem that requires this change, is that RevenueCat uses NSUserDefaults as a data layer. The actual problem is using the default instance and not a separate standalone instance specially instantiated for RevenueCat.

This means when NSUserDefaults is reset/reloaded/cleared, then RevenueCat will lose track of all persisted data.

This might happen automatically for some reason, abnormalities with NSUserDefaults shared instance that puts RevenueCat in an undefined state.

Fix

With this introduction for the problem, the solution is simply taking in an optional string ID as a parameter within Purchases.Configure that would create the standalone NSUserDefaults instance automatically for us. Like this solution in an issue from iOS repo. Or at least just make it so that RevenueCat uses a hardcoded NSUserDefaults domain ID.

[om-ha]

Temporary Fix

For reference until this is patched, I actually made a platform channel to fix this. In case if anybody is interested:

Inside AppDelegate.swift -> didFinishLaunchingWithOptions -> create a new FlutterMethodChannel (for our example "myapp_platform_channel") and inside setMethodCallHandler callback parameter FlutterMethodCallHandler add the following:

// MARK: `setupRevenueCatPurchasesCupertino` method
if call.method == "setupRevenueCatPurchasesCupertino" {
    let argumentsDictionary = call.arguments as? Dictionary<String, Any?>
    let apiKey = argumentsDictionary?["apiKey"] as? String
    self.setupRevenueCatPurchasesCupertino(result: result, apiKey: apiKey)
    return
}

Then within AppDelegate class, create this private instance method:

// MARK:- RevenueCat Method Channel
private func setupRevenueCatPurchasesCupertino(result: FlutterResult, apiKey: String?)  {
    let userDefaultsDomain = "com.yourdomain.yourapp.revenuecat"
    let revenueCatAPIKey = apiKey ?? "hard_code_your_api_key_if_you_dare"
    
    // create UserDefaults instance/domain for RevenueCat so our app wouldn't overwrite it
    guard let revenueCatUserDefaults = UserDefaults.init(suiteName: userDefaultsDomain) else {
        let errorMessage = "RevenueCat Error: can't create user defaults for RevenueCat domain"
        print(errorMessage)
        result(false)
        return
    }
    
    // configure/setup/initialize RevenueCat Singleton Instance
    Purchases.configure(withAPIKey: revenueCatAPIKey,
                        appUserID: nil,
                        observerMode: false,
                        userDefaults: revenueCatUserDefaults)
    
    // finish execution
    result(true)
}

Create myapp_platform_channel.dart

import 'dart:io';

import 'package:flutter/services.dart';

class MyAppPlatformChannel {
  static const platform = const MethodChannel("myapp_platform_channel");

  Future<void> setupRevenueCatPurchasesCupertino(String apiKey) async {
    try {
      await platform.invokeMethod(
          "setupRevenueCatPurchasesCupertino", {"apiKey": apiKey});
    } catch (e) {
      print(e.message);
    }
  }
}

Finally, setup your RevenueCat instance like this:

// Setup
if (Platform.isIOS) {
  // iOS -- platform-specific setup to account for a bug where AppUserID is null (since library is using NSDefaults)
  // - https://github.com/RevenueCat/purchases-ios/issues/156
  // - https://github.com/RevenueCat/purchases-ios/issues/151
  // - https://github.com/RevenueCat/purchases-flutter/issues/49
  await MyAppPlatformChannel()
      .setupRevenueCatPurchasesCupertino(revenueCatSDKPublicKey);
} else if (Platform.isAndroid) {
  // Android -- normal setup
  await Purchases.setup(
    revenueCatSDKPublicKey,
  );
}

[aboedo]

Hi! Thanks for reporting and for posting a workaround! I'm sure that'll help folks until we get a fix out.
We'll make the parameter public on the next flutter release. I'll keep this open until then

[aboedo]

forgot to close this one out, but this has been integrated into version 1.2.0