VWO FME Flutter SDK

Overview

The VWO Feature Management and Experimentation SDK (VWO FME Flutter SDK) enables Flutter developers to integrate feature flagging and experimentation into their applications. This SDK provides full control over feature rollout, A/B testing, and event tracking, allowing teams to manage features dynamically and gain insights into user behavior.

Requirements

The Flutter SDK supports:

• iOS 12.0 or higher
• Android API level 21 or higher

SDK Installation

Add the VWO FME Flutter SDK to your project's pubspec.yaml file:

dependencies:
  vwo_fme_flutter_sdk: ^<latestVersion>

Then run:

flutter pub get

Latest version of SDK can be found in pub.dev

Basic Usage

The following example demonstrates initializing the SDK with a VWO account ID and SDK key, setting a user context, checking if a feature flag is enabled, and tracking a custom event.

import 'package:vwo_fme_flutter_sdk/vwo.dart';
import 'package:vwo_fme_flutter_sdk/vwo/models/vwo_init_options.dart';
import 'package:vwo_fme_flutter_sdk/vwo/models/vwo_user_context.dart';
import 'package:vwo_fme_flutter_sdk/vwo/models/get_flag.dart';
import 'package:vwo_fme_flutter_sdk/logger/log_transport.dart';

// Create a custom logger implementation
class DartLogger implements LogTransport {
  @override
  void log(String level, String? message) {
    if (message == null) return;
    print("FME-Flutter: [$level] $message");
  }
}

// Initialize VWO SDK with logger configuration
var transport = <String, dynamic>{};
transport["defaultTransport"] = DartLogger();

var logger = <Map<String, dynamic>>[];
logger.add(transport);

final vwoInitOptions = VWOInitOptions(
  sdkKey: SDK_KEY,
  accountId: ACCOUNT_ID,
  logger: {"level": "TRACE", "transports": logger},
);

// Create VWO instance with the vwoInitOptions
final vwoClient = await VWO.init(vwoInitOptions);

// Create VWOUserContext object
final context = VWOUserContext(
    id: "unique_user_id",
    customVariables: {"key1": 21, "key2":"value"}
);

// Get the GetFlag object for the feature key and context
final featureFlag = await vwoClient?.getFlag(
  featureKey: "feature_key",
  context: context,
);

if (featureFlag != null) {
  // Get the flag value
  final isFeatureFlagEnabled = featureFlag.isEnabled();

  // Get the variable value for the given variable key and default value
  dynamic variable = featureFlag.getVariable("feature_flag_variable", "default-value");
}

// Track the event for the given event name and context
final properties = {"cartvalue": 10};
await vwoClient?.trackEvent(
  eventName: "event-name",
  context: context,
  eventProperties: properties,
);

// Send attributes data
final attributes = {
  "attributeName": "attributeValue"
};
await vwoClient?.setAttribute(
  attributes: attributes,
  context: context,
);

Advanced Configuration Options

To customize the SDK further, additional parameters can be passed to the init() API. Here's a table describing each option:

Parameter	Description	Required	Type	Example
accountId	VWO Account ID for authentication.	Yes	Integer	123456
sdkKey	SDK key corresponding to the specific environment to initialize the VWO SDK Client. You can get this key from VWO Application.	Yes	String	'32-alpha-numeric-sdk-key'
pollInterval	Time interval for fetching updates from VWO servers (in milliseconds).	No	Integer	60000
cachedSettingsExpiryTime	Controls the duration (in milliseconds) the SDK uses cached settings before fetching new ones.	No	Integer	60000
batchMinSize	Uploads are triggered when the batch reaches this minimum size.	No	Integer	10
batchUploadTimeInterval	Specifies the time interval (in milliseconds) for periodic batch uploads.	No	Integer	60000
logger	Custom logger configuration for controlling log levels and implementing custom logging behavior.	No	Object	See Logger section

User Context

The context object uniquely identifies users and is crucial for consistent feature rollouts. A typical context includes an id for identifying the user. It can also include other attributes that can be used for targeting and segmentation, such as customVariables.

Parameters Table

The following table explains all the parameters in the context object:

Parameter	Description	Required	Type	Example
id	Unique identifier for the user.	Yes	String	'unique_user_id'
customVariables	Custom attributes for targeting.	No	Object	{ age: 25, location: 'US' }

Example

final userContext = VWOUserContext(
    id: USER_ID,
    customVariables: {
        "age": 25,
        "location": "US"
    }
);

Basic Feature Flagging

Feature Flags serve as the foundation for all testing, personalization, and rollout rules within FME. To implement a feature flag, first use the getFlag API to retrieve the flag configuration. The getFlag API provides a simple way to check if a feature is enabled for a specific user and access its variables.

Parameter	Description	Required	Type	Example
featureKey	Unique identifier of the feature flag	Yes	String	'new_checkout'
context	Object containing user identification and contextual information	Yes	Object	VWOUserContext()

Example usage:

final featureFlag = await vwoClient?.getFlag(
  featureKey: "featureKey",
  context: context,
);

if (featureFlag != null) {
  // Get the flag value
  final isFeatureFlagEnabled = featureFlag.isEnabled();

  // Get the variable value for the given variable key and default value
  final variable = featureFlag.getVariable("feature_flag_variable", "default-value") as String;
}

Custom Event Tracking

Feature flags can be enhanced with connected metrics to track key performance indicators (KPIs) for your features. These metrics help measure the effectiveness of your testing rules by comparing control versus variation performance, and evaluate the impact of personalization and rollout campaigns. Use the trackEvent API to track custom events like conversions, user interactions, and other important metrics:

Parameter	Description	Required	Type	Example
eventName	Name of the event you want to track	Yes	String	'purchase_completed'
context	Object containing user identification and other contextual information	Yes	Object	VWOUserContext()
eventProperties	Additional properties/metadata associated with the event	No	Object	{"amount": 10}

Example usage:

final context = VWOUserContext(
    id: userId
);
final properties = {"cartvalue": 10};

await vwoClient.trackEvent(
  eventName: "event-name",
  context: context,
  eventProperties: properties,
);

Pushing Attributes

User attributes provide rich contextual information about users, enabling powerful personalization. The setAttribute method provides a simple way to associate these attributes with users in VWO for advanced segmentation. Here's what you need to know about the method parameters:

Parameter	Description	Required	Type	Example
attributes	Map of attribute key and value to be set	Yes	Object	{"price": 99}
context	Object containing user identification and other contextual information	Yes	Object	VWOUserContext()

Example usage:

final context = VWOUserContext(
    id: userId
);
final attributes = {"price": 99};
await vwoClient?.setAttribute(
  attributes: attributes,
  context: context,
);

Polling Interval Adjustment

The pollInterval is an optional parameter that allows the SDK to automatically fetch and update settings from the VWO server at specified intervals. Setting this parameter ensures your application always uses the latest configuration.

final vwoInitOptions = VWOInitOptions(
        sdkKey: SDK_KEY,
        accountId: ACCOUNT_ID,
        pollInterval: 60000
)    

// Create VWO instance with the vwoInitOptions
final vwoClient = await VWO.init(vwoInitOptions);

Logger

VWO by default logs all ERROR level messages to the console. To gain more control over VWO's logging behavior, you can use the logger parameter in the init configuration.

Parameter	Description	Required	Type	Example
level	Log level to control verbosity of logs	Yes	String	TRACE
transports	Custom logger implementation	No	Object	See example below

Example: Implement custom logger

The transports parameter allows you to implement custom logging behavior by providing your own logging functions. You can define handlers for different log levels (TRACE, DEBUG, INFO, WARN, ERROR) to process log messages according to your needs.

// Create a custom logger implementation
class DartLogger implements LogTransport {
  @override
  void log(String level, String? message) {
    if (message == null) return;
    print("FME-Flutter: [$level] $message");
  }
}

// Configure logger in VWO initialization
var transport = <String, dynamic>{};
transport["defaultTransport"] = DartLogger();

var logger = <Map<String, dynamic>>[];
logger.add(transport);

final vwoInitOptions = VWOInitOptions(
  sdkKey: SDK_KEY,
  accountId: ACCOUNT_ID,
  logger: {"level": "TRACE", "transports": logger},
);

final vwoClient = await VWO.init(vwoInitOptions);

Authors

• Swapnil Chaudhari

Version History

The version history tracks changes, improvements and bug fixes in each version. For a full history, see the CHANGELOG.md.

Contributing

We welcome contributions to improve this SDK! Please read our contributing guidelines before submitting a PR.

Code of Conduct

Code of Conduct

License

Apache License, Version 2.0

Copyright (c) 2024-2025 Wingify Software Pvt. Ltd.