iOS SDK

This guide provides detailed information about our iOS SDK. All of our SDKs are open source. Go to our iOS SDK GitHub repository to see the source code.

Language Support

This library is compatible with iOS and tvOS deployment target versions 9.0+, macOS 10.11+, and watchOS 7.0+. Xcode 12 and later is also required, but we recommend the minimum version necessary to publish apps on the AppStore.

Initialization

To get started, set up Split in your code base with the two following steps.

1. Import the SDK into your project

Swift Package Manager

You can import the SDK in your project by using Swift Package Manager. This can be done through XCode or by editing manually the Package.swift file to add the iOS SDK repository as a dependency.

CocoaPods

You can also import the SDK into your Xcode project using CocoaPods, adding it in your Podfile.

pod 'Split', '~> 2.19.1'

Carthage

This is another option to import the SDK. Just add it in your Cartfile.

github "splitio/ios-client" 2.19.1

Once added, follow the steps provided in the Carthage Readme.

2. Instantiate the SDK and create a new Split client

The first time that the SDK is instantiated, it starts background tasks to update an in-memory cache and in-storage cache with small amounts of data fetched from Split servers. This process can take up to a few hundred milliseconds depending on the size of the data.

If the SDK is asked to evaluate which treatment to show to a customer for a specific split while it is in this intermediate state, it may not have the data necessary to run the evaluation. In this case, the SDK does not fail, rather, it returns the control treatment.

After the first initialization, the fetched data is stored. Further initializations fetch data from that cache and the configuration is available immediately.

We recommend instantiating the SDK once as a singleton and reusing it throughout your application.

Include the API key for the environment that you are setting up the SDK for. The API key is available on your Organization Settings page, on the APIs tab. Choose the "client-side" type. This is a special type of API token with limited privileges to be used for the untrustable browsers or mobile clients. Learn more about API keys.

import Split

// Your Split API-KEY
let apiKey: String = "YOUR_API_KEY"

//User Key
let key: Key = Key(matchingKey: "key")

//Split Configuration
let config = SplitClientConfig()

//Split Factory
let builder = DefaultSplitFactoryBuilder()
let factory = builder.setApiKey(apiKey).setKey(key).setConfig(config).build()

//Split Client
let client = factory?.client

Using the SDK

Basic use

To make sure the SDK is properly loaded before asking it for a treatment, wait until the SDK is ready as shown below. We set the client to listen for the sdkReady event triggered by the SDK before asking for an evaluation.

Once the sdkReady event fires, you can use the getTreatment method to return the proper treatment based on the split name you pass and the key you passed when instantiating the SDK.

From there, you need to use an if-else-if block as shown below and plug the code in for the different treatments that you defined in the Split user interface. Make sure to remember the final else branch in your code to handle the client returning control.

client?.on(event: SplitEvent.sdkReady) {
  // Evaluate key in Split
  let treatment = client?.getTreatment("SPLIT_NAME")

  if treatment == "on" {
      // insert code here to show on treatment
  } else if treatment == "off" {
      // insert code here to show off treatment
  } else {
      // insert your control treatment code here
  }
}
client?.on(event: SplitEvent.sdkReadyTimedOut) {
  //handle for timeouts here
  print("SDK time out")
}

Also, a sdkReadyFromCache event is available, which allows you to be aware of when the SDK has loaded data from cache. This way it is ready to evaluate splits using those locally cached definitions.

client?.on(event: SplitEvent.sdkReadyFromCache) {
  // Evaluate key in Split
  let treatment = client?.getTreatment("SPLIT_NAME")

  if treatment == "on" {
      // insert code here to show on treatment
  } else if treatment == "off" {
      // insert code here to show off treatment
  } else {
      // insert your control treatment code here
  }
}

Shutdown

Before letting your app shut down, call destroy() as it gracefully shuts down the Split SDK by stopping all background threads, clearing caches, closing connections, and flushing the remaining unpublished impressions and events.

client?.destroy()

Also, this method has a completion closure which can be used to run some code after destroy was executed. For instance, the following snippet waits until destroy has finished to continue execution:

let semaphore = DispatchSemaphore(value: 0)
client?.destroy(completion: {
    _ = semaphore.signal()
})
semaphore.wait()

After destroy() is called, any subsequent invocations to the client.getTreatment() or manager methods result in control or empty list respectively.

Multiple evaluations at once

In some instances, you may want to evaluate treatments for multiple splits at once. Use the getTreatments method of the Split client to do this. Simply pass a list of the split names you want treatments for and the method returns an object with the results.

let splitList = ["SPLIT_NAME_1", "SPLIT_NAME_2", "SPLIT_NAME_3"]
let treatments = client?.getTreatments(splits: splitList, attributes: nil)

// treatments will have the following form:
// {
//   "SPLIT_NAME_1": "result_1",
//   "SPLIT_NAME_2": "result_2",
//   "SPLIT_NAME_3": "result_3"
// }

Attribute syntax

To target based on custom attributes, the SDK's getTreatment method needs to be passed an attribute map at runtime.

In the example below, we are rolling out a split to users. The provided attributes plan_type, registered_date, permissions, paying_customer, and deal_size are passed to the getTreatment call. These attributes are compared and evaluated against the attributes used in the Rollout plan as defined in the Split Web console to decide whether to show the on or off treatment to this account.

The getTreatment method supports five types of attributes: strings, numbers, dates, booleans, and sets. The proper data type and syntax for each are:

• Strings: Use type String.
• Numbers: Use type Int64.
• Dates: Use the value TimeInterval. For instance, the value for the registered_date attribute below is Date().timeIntervalSince1970, which is a TimeInterval value.
• Booleans: Use type Bool.
• Sets: Use type [String].

var attributes: [String:Any] = [:]

attributes["plan_type"] = "growth"
attributes["registered_date"] = Date().timeIntervalSince1970
attributes["deal_size"] = 1000
attributes["paying_customer"] = true
let perms: [String] = ["read", "write"];
attributes["permissions"] = perms

// See client initialization above
let treatment = client?.getTreatment("SPLIT_NAME", attributes: attributes)

if treatment == "on" {
    // insert code here to show on treatment
} else if treatment == "off" {
    // insert code here to show off treatment
} else {
    // insert your control treatment code here
}

Binding attributes to the client

Attributes can be bound to the client at any time during the SDK lifecycle. These attributes will be stored in memory and used in every evaluation to avoid the need for keeping the attribute set accessible through the whole app. These attributes can be cached into the persistent caching mechanism of the SDK making them available for future sessions, as well as part of the SDK_READY_FROM_CACHE flow by setting the persistentAttributesEnabled to true. No need to wait for your attributes to be loaded at every session before evaluating flags that use them.

When an evaluation is called, the attributes provided (if any) at evaluation time are combined with the ones already loaded into the SDK memory, with the ones provided at function execution time take precedence, enabling for those attributes to be overridden or hidden for specific evaluations.

The snippet below shows how to update these attributes:

@objc public protocol SplitClient {

  /**
    Set one single attribute and returns true unless there is an issue storing it.
    If `persistentAttributesEnabled` config is enabled, the attribute is also written to the persistent cache.
  */
  func setAttribute(name: String, value: Any) -> Bool

  /**
    Retrieves the value of a given attribute stored in cache.
  */
  func getAttribute(name: String) -> Any?

  /**
    Set multiple attributes and returns true unless there is an issue storing them.
    If `persistentAttributesEnabled` config is enabled, the attributes are also written to the persistent cache.
  */
   func setAttributes(_ values: [String: Any]) -> Bool

  /**
    Retrieves a Map with the values of all attributes stored in cache.
  */
  func getAttributes() -> [String: Any]?

  /**
    Remove one single attribute and returns true unless there is an issue deleting it.
    If `persistentAttributesEnabled` config is enabled, the attribute is also deleted from the persistent cache and won't be available in a subsequent session.
  */
  func removeAttribute(name: String) -> Bool

  /**
    Clear the whole attribute cache and return true unless there is an issue with the operation and some attributes might still be cached.
    If `persistentAttributesEnabled` config is enabled, the attributes are also deleted from the persistent cache and won't be available in a subsequent session.
  */
  func clearAttributes() -> Bool
}

// Prepare a Map with several attributes
var attributes: [String:Any] = [:]
attributes["plan_type"] = "growth"
attributes["registered_date"] = Date().timeIntervalSince1970
attributes["deal_size"] = 1000

// Now set these on the client
let result = client.setAttributes(attributes)

// Set one attribute
let result = client.setAttribute(name: "registered_date", value: Date().timeIntervalSince1970)

// Get an attribute
let result = client.getAttribute(name: "registered_date")

// Get all attributes
let result = client.getAttributes()

// Remove an attribute
let result = client.removeAttribute(name: "deal_size")

// Remove all attributes
let result = client.clearAttributes()

Get Treatments with Configurations

To leverage dynamic configurations with your treatments, use the getTreatmentWithConfig method. This method returns an object containing the treatment and associated configuration.

The config element is a stringified version of the configuration JSON defined in the Split web console. If there is no configuration defined for a treatment, the SDK returns null for the config parameter.

This method takes the exact same set of arguments as the standard getTreatment method. See below for examples on proper usage:

let result = client.getTreatmentWithConfig("new_boxes", attributes: attributes)
let config = try? JSONSerialization.jsonObject(with: result.config.data(using: .utf8)!, options: []) as? [String: Any]
let treatment = result.treatment

If you need to get multiple evaluations at once, you can also use getTreatmentsWithConfig. The method takes the exact same arguments as the getTreatments method but just returns a mapping of split names to splitResults instead of strings. Refer to the example below.

let splitList = ["SPLIT_NAME_1", "SPLIT_NAME_2", "SPLIT_NAME_3"]
let treatments = client?.getTreatmentsWithConfig(splits: splitList, attributes: nil)

// treatments will have the following form:
// {
//   "SPLIT_NAME_1": { "treatment": "on", "config": "{ \"color\":\"red\" }"},
//   "SPLIT_NAME_2": { "treatment": "visa", "config": "{ \"color\":\"red\" }"}
// }

Track

Use the track method to record any actions your customers perform. Each action is known as an event and corresponds to an event type. Calling track through one of our SDKs or via the API is the first step to getting experimentation data into Split and allows you to measure the impact of your splits on your users' actions and metrics.

Learn more about using track events in splits.

In the examples below, you can see that the .track() method can take up to four arguments. The proper data type and syntax for each are:

• TRAFFIC_TYPE: The traffic type of the key in the track call. The expected data type is String. You can only pass values that match the names of traffic types that you have defined in your instance of Split.
• EVENT_TYPE: The event type that this event should correspond to. The expected data type is String. Full requirements on this argument are:
  • Contains 63 characters or fewer.
  • Starts with a letter or number.
  • Contains only letters, numbers, hyphen, underscore, or period.
  • This is the regular expression we use to validate the value: [a-zA-Z0-9][-_\.a-zA-Z0-9]{0,62}.
• VALUE: (Optional) The value used in creating the metric. This field can be sent in as null or 0 if you intend to only use the count function when creating a metric. The expected data type is Double.
• PROPERTIES: (Optional) An object of key value pairs that can be used to filter your metrics. Refer to Event property capture guide to learn about this topic. Split currently supports three types of properties: strings, numbers, and booleans.

The track method returns a boolean value of true or false to indicate whether or not the SDK was able to successfully queue the event sent back to Split's servers on the next event post. The SDK returns false if the current queue size is equal to the config set by eventsQueueSize or if an incorrect input to the track method is provided.

In case a bad input is provided, you can read more about our SDK's expected behavior in our Events guide.

// Event without a value
let resp = client?.track(trafficType: "TRAFFIC_TYPE", eventType: "EVENT-TYPE")
// Example
let resp = client?.track(trafficType: "user", eventType: "page_load_time")

// If you would like to associate a value to an event
let resp = client?.track(trafficType: "TRAFFIC_TYPE", eventType: "EVENT-TYPE", value: VALUE)
// Example  
let resp = client?.track(trafficType: "user", eventType: "page_load_time", value: 83.334)

// If you would like to associate just properties to an event
let resp = client?.track(trafficType: "TRAFFIC_TYPE", eventType: "EVENT-TYPE", properties: PROPERTIES)
// Example  
let properties: [String:Any] = ["package": "premium", "discount": 50, "admin": true]
let resp = client?.track(trafficType: "user", eventType: "page_load_time", properties: properties)

// If you would like to send an event but you've already defined the traffic type in the config of the client
let resp = client?.track(eventType: "EVENT-TYPE")
// Example
let resp = client?.track(eventType: "page_load_time")

// If you would like to associate a value to an event and you've already defined the traffic type in the config of the client
let resp = client.track(eventType: "EVENT-TYPE", value: VALUE)
// Example  
let resp = client?.track(eventType: "page_load_time", value: 83.334)

// If you would like to associate properties to an event and you've already defined the traffic type in the config of the client
let resp = client.track(eventType: "EVENT-TYPE", properties: PROPERTIES)
// Example  
let properties: [String:Any] = ["package": "premium", "discount": 50, "admin": true]
let resp = client?.track(eventType: "page_load_time", proerties: properties)

Manager

Use the Split Manager to get a list of features available to the Split client.

To instantiate a Manager in your code base, use the same factory that you used for your client.

let apiKey: String = "YOUR_API_KEY"
let key: Key = Key(matchingKey: "key")
let config = SplitClientConfig()
let builder = DefaultSplitFactoryBuilder()
let factory =
builder.setApiKey(apiKey).setKey(key).setConfig(config).build()
let manager = factory?.manager

The Manager then has the following properties and methods available.

/**
 * Retrieves the Splits that are currently registered with the
 * SDK.
 *
 * @return an array of SplitView or empty.
 */
var splits: [SplitView] { get }

/**
 * Returns the names of features (or Splits) registered with the SDK.
 *
 * @return an array of String (Split Feature Names) or empty
 */
var splitNames: [String] { get }

/**
 * Returns the Splits registered with the SDK of this name.
 *
 * @return SplitView or nil
 */
func split(featureName: String) -> SplitView?

The SplitView class referenced above has the following structure.

@objc public class SplitView: NSObject, Codable {

    public var name: String?
    public var trafficType: String?
    public var killed: Bool?
    public var treatments: [String]?
    public var changeNumber: Int64?

}

Configuration

The SDK has a number of knobs for configuring performance. Each knob is tuned to a reasonable default. However, you can override the value while instantiating the SDK. The parameters available for configuration are shown below.

To set each of the parameters defined above, use the syntax below:

import Split

// Your Split API-KEY
let apiKey: String = "YOUR_API_KEY"

//User Key
let key: Key = Key(matchingKey: "key")

//Split Configuration
let config = SplitClientConfig()
config.impressionRefreshRate = 30
config.isDebugModeEnabled = false
let syncConfig = SyncConfig.builder()
                    .addSplitFilter(SplitFilter.byName(["SPLIT_NAME_1", "SPLIT_NAME_2"]))
                    .build()
config.sync = syncConfig

//Split Factory
let builder = DefaultSplitFactoryBuilder()
let factory =
builder.setApiKey(apiKey).setKey(key).setConfig(config).build()

//Split Client
let client = factory?.client

User consent

The SDK allows you to disable the tracking of events and impressions until user consent is explicitly granted or declined.

The userConsent configuration parameter lets you set the initial consent status of the SDK instance, and the factory method setUserConsent(enabled: Bool) lets you grant (enable) or decline (disable) the dynamic data tracking.

The following are the three possible initial states:

• 'GRANTED'. The user grants consent for tracking events and impressions. The SDK sends them to the Split cloud. This is the default value if the userConsent param is not defined.
• 'DECLINED'. The user declines consent for tracking events and impressions. The SDK does not send them to the Split cloud.
• 'UNKNOWN'. The user neither grants nor declines consent for tracking events and impressions. The SDK tracks them in its internal storage, and eventually either sends them or not if the consent status is updated to 'GRANTED' or 'DECLINED' respectively. The status can be updated at any time with the setUserConsent factory method.

  let config = SplitClientConfig()
  // Overwrites the initial consent status of the factory instance, which is 'GRANTED' by default.
  // 'UNKNOWN' status represents that the user has neither granted nor declined consent for tracking data, 
  // so the SDK will locally track data but not send it to Split cloud until consent is changed to 'GRANTED'.
  config.userConsent = .unknown
  guard let factory = DefaultSplitFactoryBuilder()
      .setApiKey("API_KEY_HERE")
      .setKey(Key(matchingKey: "user_key"))
      .setConfig(config)
      .build() else {
      return
  }

  // Changed User Consent status to 'GRANTED'. Data will not be sent to Split cloud.
  factory.setUserConsent(enabled: true);
  // Changed User Consent status to 'DECLINED'. Data will not be sent to Split cloud.
  factory.setUserConsent(enabled: false);

  // The 'getUserConsent' method returns User Consent status.
  // We expose the constants for customer checks and tracking.
  if (factory.userConsent == UserConsent.declined) {
      print("USER CONSENT DECLINED");
  }
  if (factory.userConsent == UserConsent.granted) {
      print("USER CONSENT GRANTED");
  }
  if (factory.userConsent == UserConsent.unknown) {
      print("USER CONSENT UNKNOWN");
  }

Localhost Mode

Features start their life on one developer's machine. A developer should be able to put code behind Splits on their development machine without the SDK requiring network connectivity. To achieve this, the Split SDK can be started in 'localhost' mode. In this mode, the SDK neither polls nor updates Split servers, rather it uses an in-memory data structure to determine what treatments to show to the customer for each of the features.

To use the SDK in localhost mode, replace the API Key with "localhost", as shown in the example below:

Since version 2.1.0, our SDK supports a new type of localhost split definition file using the YAML format. This new format allows the user to map different keys to different treatments within a single split, and add configurations to them. This file must be included into the project bundle and it is used as an initial file. It is copied to the cache folder, then it can be edited while app is running to simulate split changes. When no file is added to the app bundle, an error occurs. The file periodically reloads. This period can be updated through the offlineRefreshRate config. Also, the refresh process can be turned off by setting this config to -1.

The new format is a list of single-key maps (one per mapping split-keys-config), defined as follows:

# - feature_name:
#     treatment: "treatment_applied_to_this_entry"
#     keys: "single_key_or_list"
#     config: "{\"desc\" : \"this applies only to ON treatment\"}"

- my_feature:
    treatment: "on"
    keys: "key"
    config: "{\"desc\" : \"this applies only to ON treatment\"}"
- some_other_feature:
    treatment: "off"
- my_feature:
    treatment: "off"
- other_feature:
    treatment: "off"
    keys: ["key_1", "key_2"]
    config: "{\"desc\" : \"this overrides multiple keys and returns off treatment for those keys\"}"

In the example above, we have four entries:

• The first entry defines that for split my_feature, the key key returns the treatment on and the on treatment is tied to the configuration {"desc" : "this applies only to ON treatment"}.
• The second entry defines that the feature some_other_feature will always return the off treatment and no configuration.
• The third entry defines that my_feature always returns off for all keys that don't match another entry. In this case, any key other than key.
• The fourth entry shows how an example to override a treatment for a set of keys.

You can set the name of the Split localhost YAML file within cache folder as shown in the example below:

// Split API-KEY must be "localhost"
let apiKey: String = "localhost"
let key: Key = Key(matchingKey: "key")
let config = SplitClientConfig()
config.splitFile = "localhost.yaml"
let builder = DefaultSplitFactoryBuilder()
self.factory =
builder.setApiKey("localhost").setKey(key).setConfig(config).build()

If SplitClientConfig.splitFile is not set, Split SDK maintains backward compatibility by trying to load the legacy file (.splits), now deprecated. In this mode, the SDK loads a local file called localhost.splits which has the following line format:

SPLIT TREATMENT

Additionally, you can include comments to the file starting a line with the # character.

Example: A sample localhost.splits file

 # This line is a comment
 # Following line has feature = FEATURE_ONE and treatment = ON
 FEATURE_ONE ON
 FEATURE_TWO OFF
 # Previous line has feature = FEATURE_TWO, treatment = OFF

By enabling debug mode, the localhost file location is logged to the console so that it's possible to open it with a text editor when working on the simulator. When using the device to run the app, the file can be modified by overwriting the app's bundle from the Device and Simulators tool.

Listener

Split SDKs send impression data back to Split servers periodically and as a result of evaluating splits. To additionally send this information to a location of your choice, define and attach an impression handler.

The SDK sends the generated impressions to the impression handler right away. As a result, be careful while implementing handling logic to avoid blocking the main thread. Generally speaking, you should create a separate thread to handle incoming impressions. Refer to the snippet below.

let config = SplitClientConfig()
config.impressionListener = { impression in
        // Do some work on main thread
        DispatchQueue.global().async {
            // Do some async work (use this most of the time!)
        }
}  

let key: Key = Key(matchingKey: "key")
let builder = DefaultSplitFactoryBuilder()
let factory =
builder.setApiKey(apiKey).setKey(key).setConfig(config).build()
let client = factory?.client

In regards with the data available here, refer to the impression objects interface and description of each field below. There are two fields in particular that are different for Swift and Obj-C so see the corresponding tab:

  feature: String?
  keyName: String?
  treatment: String?
  time: Int64?
  changeNumber: Int64?
  label: String?
  bucketingKey: String?
  attributes: [String: Any]?

Flush

The flush() method sends the data stored in memory (impressions and events) to Split cloud and clears the successfully posted data. If a connection issue is experienced, the data will be sent on the next attempt.

client.flush()

Background synchronization

Since version 2.11.0, background synchronization is available for devices having iOS 13+.
To enable this feature, just follow the next 4 steps:

1. Enable Background Mode Fetch capability for your app.
2. Add the Split SDK background sync task identifier io.split.bg-sync.task to the Permitted background task scheduler identifiers section of the Info.plist .
3. Set the Split config flag synchronizeInBackground to true .

let config = SplitClientConfig()
config.synchronizeInBackground = true

...

4. Schedule the background sync during app startup. e.g., application(_:didFinishLaunchingWithOptions:)

SplitBgSynchronizer.shared.schedule()

...

Advanced use cases

This section describes advanced use cases and features provided by the SDK.

Instantiate multiple SDK clients

In versions previous to 2.14.0, you had to create more that one SDK instance to evaluate for different users IDs. From v2.14.0 on, Split supports the ability to create multiple clients, one for each user ID. For example, if you need to roll out splits for different user IDs, you can instantiate multiple clients, one for each ID. You can then evaluate them using the corresponding client. You can do this using the example below:

// Create factory
let key = Key(matchingKey: "anonymous_user")
let config = SplitClientConfig()
let factory = DefaultSplitFactoryBuilder().setApiKey(authorizationKey)
    .setKey(key)
    .setConfig(config).build()

// Now when you call factory.client, the SDK will create a client
// using the anonymous_user key
// you passed in during the factory creation
let anonymousClient = factory.client

// To create another client for a user instead, pass in a User ID
let userClient = factory.client(matchingKey: "user_id")

// Add events handler for each client to be notified when SDK is ready
anonymousClient.on(event: SplitEvent.sdkReady, execute: {
  // anonymousClient is ready to evaluate
  // Check treatment for anonymous users
  let accountPermissioningTreatment = anonymousClient.getTreatment("some_feature")
})

userClient.on(event: SplitEvent.sdkReady, execute: {
  // userClient is ready to evaluate
  // Check treatment for the feature and user_id
  let userPollTreatment = userClient.getTreatment("some_feature")
})

Subscribe to events

You can listen for four different types of events from the SDK.

• sdkReadyFromCache - The SDK is ready to evaluate using cached data (which might be stale). If conditions are met, this event will be emitted almost immediately since access to the cache is synchronous. Otherwise it won't fire.
• sdkReady - The SDK is ready to be used and has the most up-to-date snapshot of your splits.
• sdkReadyTimedOut - This event fires if there is no last known configuration in disk cache, and the SDK could not acquire the information from our servers after a given period of time, determined by the sdkReadyTimeOut parameter in SplitClientConfig. When this event fires, it doesn't mean the SDK initialization is interrupted. The sdkReady event may still fire at a later time if or when the SDK finishes downloading the necessary information from the servers. This may happen with slow connections or environments which have many splits, segments, or dynamic configurations.
• sdkUpdated - This event fires whenever a split or segment is changed. Use this if you want to reload your app every time you make a change in the Split Web console.

SDK event handling is done through the function on(event:execute:), which receives a closure as an event handler.

The code within the closure is executed on the main thread. For that reason, running code in the background must be done explicitly.

The syntax to listen for an event is shown below.

...
let client = factory.client

client.on(event: SplitEvent.sdkReady, execute: {
    // The client is ready to evaluate treatments according to the latest split definitions
    // Do some stuff on main thread
})

// Or
client.on(event: SplitEvent.sdkReadyTimedOut) {
  // This callback will be called if and only if the client is configured with ready timeout and
  // is not ready for that time or if the API key is wrong. 
  // You can still call getTreatment() but it could return CONTROL.

  // Do some stuff on main thread
}

client.on(event: SplitEvent.sdkReadyFromCache) {
  // Fired after the SDK could confirm the presence of the Split data.
  // This event fires quickly, since there's no actual fetching of information.
  // Keep in mind that data might be stale, this is NOT a replacement of sdkReady.

  // Do some stuff on main thread
}

client.on(event: SplitEvent.sdkUpdated) {
  // fired each time the client state change. 
  // For example, when a Split or a Segment changes.

  // Do some stuff on main thread
}

...