Featureflip Flutter SDK

Flutter SDK for Featureflip — evaluate feature flags in Flutter apps with real-time updates.

Installation

Add to your pubspec.yaml:

dependencies:
  featureflip: ^2.0.0

Then run:

flutter pub get

Quick Start

import 'package:featureflip/featureflip.dart';

final config = FeatureflipConfig(clientKey: 'your-client-sdk-key');
final client = FeatureflipClient.get('your-client-sdk-key', config: config);

await client.initialize();

final enabled = client.boolVariation('my-feature', defaultValue: false);

if (enabled) {
  print('Feature is enabled!');
}

await client.close();

Configuration

final config = FeatureflipConfig(
  clientKey: 'your-client-sdk-key',
  baseUrl: 'https://eval.featureflip.io',       // Evaluation API URL (default)
  context: {'user_id': '123'},                    // Initial evaluation context
  streaming: true,                                // SSE for real-time updates (default)
  pollIntervalSeconds: 30,                        // Polling interval in seconds
  flushIntervalSeconds: 30,                       // Event flush interval in seconds
  flushBatchSize: 100,                            // Events per batch
  initTimeoutSeconds: 10,                         // Max seconds to wait for initialization
);

Lifetime

FeatureflipClient.get() is the only way to obtain a client. Calling it multiple times with the same SDK key returns handles that share a single underlying connection — safe for any registration lifetime (singleton, scoped, transient).

final client1 = FeatureflipClient.get('key', config: config);
final client2 = FeatureflipClient.get('key', config: config);

// client1 and client2 share one connection (refcounted).
// The connection shuts down only when the last handle is closed.

await client1.close(); // decrements refcount
await client2.close(); // refcount → 0, connection shut down

Evaluation

// Boolean flag
final enabled = client.boolVariation('feature-key', defaultValue: false);

// String flag
final tier = client.stringVariation('pricing-tier', defaultValue: 'free');

// Number flag
final limit = client.numberVariation('rate-limit', defaultValue: 100.0);

// JSON flag
final uiConfig = client.jsonVariation('ui-config', defaultValue: {'theme': 'light'});

Identify

Re-evaluate all flags with a new context (e.g., after login):

await client.identify({'user_id': '123', 'plan': 'pro'});

Event Tracking

// Track custom events
client.track('checkout-completed', metadata: {'total': 99.99});

// Force flush pending events
await client.flush();

Flutter Widget Integration

Use FeatureflipProvider with ListenableBuilder for reactive flag values:

import 'package:featureflip/featureflip.dart';

class MyApp extends StatelessWidget {
  final FeatureflipClient client;
  const MyApp({super.key, required this.client});

  @override
  Widget build(BuildContext context) {
    return ListenableBuilder(
      listenable: client.flagProvider,
      builder: (context, _) {
        final showBanner = client.flagProvider.boolVariation(
          'show-banner',
          defaultValue: false,
        );
        return showBanner ? const BannerWidget() : const SizedBox.shrink();
      },
    );
  }
}

Testing

Use forTesting() to create a client with predetermined flag values — no network calls.

final client = FeatureflipClient.forTesting({
  'my-feature': true,
  'pricing-tier': 'pro',
});

client.boolVariation('my-feature', defaultValue: false);     // true
client.stringVariation('pricing-tier', defaultValue: 'free'); // 'pro'
client.boolVariation('unknown', defaultValue: false);         // false (default)

For test isolation, call resetForTesting() in your test teardown:

tearDown(() {
  FeatureflipClient.resetForTesting();
});

Features

  • Client-side evaluation — Flags evaluated server-side, only values returned
  • Real-time updates — SSE streaming with automatic polling fallback
  • Singleton by construction — Same SDK key always shares one connection
  • Refcounted lifecycle — Connection shuts down when the last handle closes
  • Event tracking — Automatic batching and background flushing
  • Test support — forTesting() factory for deterministic unit tests
  • Flutter integration — FeatureflipProvider for reactive flag values
  • Lifecycle management — Automatic pause/resume on app lifecycle changes

Requirements

  • Flutter 3.24+
  • Dart 3.5+

License

Apache-2.0

Libraries

featureflip