LaunchDarkly Developer Documentation

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LaunchDarkly provides feature flags as a service for Java · Python · Ruby · Go · Node.js · PHP · .NET. Control feature launches -- who sees what and when -- without multiple code deploys. Easy dashboard for phased rollouts, targeting and segmenting.
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iOS SDK Reference

This reference guide documents all of the methods available in our iOS SDK, and explains in detail how these methods work. If you want to dig even deeper, our SDKs are open source-- head to our iOS SDK GitHub repository to look under the hood.

Getting started

If you haven't taken a look at our Quickstart guide yet, we recommend starting there to see how install our SDK into your iOS application.

Once the SDK is installed, you'll want to create a single, shared instance of LDClient, passing in the client configuration object and a user:

 LDConfigBuilder *config = [[LDConfigBuilder alloc] init];
 [config withMobileKey:@"YOUR_MOBILE_KEY"];
 LDUserBuilder *user = [[LDUserBuilder alloc] init];
 user = [user withKey:@"aa0ceb"];
[[LDClient sharedInstance] start:config userBuilder:user];
let config = LDConfigBuilder()

var user = LDUserBuilder()
user = user.withKey("aa0ceb")

LDClient.sharedInstance().start(config, userBuilder: user)

Mobile keys

Be sure to use a mobile key from your Environments page. Never embed a server-side SDK key into a mobile application.

Customizing your client

You can also pass other custom parameters to the client via the configuration object:

[config withConnectionTimeout:10]; 
[config withFlushInterval:10];  
[[LDClient sharedInstance] start:config userBuilder:user];
LDClient.sharedInstance().start(config, userBuilder: user)

Here, we've customized the client connect and flush interval parameters.


Feature flag targeting and rollouts are all determined by the user you pass to your client. In our iOS SDK, we use a builder pattern to make it easy to construct users. Here's an example:

LDUserBuilder *user = [[LDUserBuilder alloc] init];

user = [user withKey:"aa0ceb"];
user = [user withFirstName:"Ernestina"];
user = [user withLastName:"Evans"];
user = [user withEmail:""];
user = [user withCustomArray:"groups" value:groups];
var user = LDUserBuilder()
user = user.withKey("aa0ceb")
user = user.withFirstName("Ernestina")
user = user.withLastName("Evans")
user = user.withEmail("")
user = user.withCustomArray("groups", value: groups)

Let's walk through this snippet. The first argument to the builder is the user's key-- in this case we've used the hash "aa0ceb". The user key is the only mandatory user attribute. The key should also uniquely identify each user. You can use a primary key, an e-mail address, or a hash, as long as the same user always has the same key. We recommend using a hash if possible.

All of the other attributes (like firstName, email, and the custom attributes) are optional. The attributes you specify will automatically appear on our dashboard, meaning that you can start segmenting and targeting users with these attributes.

In addition to built-in attributes like names and e-mail addresses, you can pass us any of your own user data by passing custom attributes, like the groups attribute in the example above.

A note on types

Most of our built-in attributes (like names and e-mail addresses) expect string values. Custom attributes values can be strings, booleans (like true or false), numbers, or lists of strings, booleans or numbers.

If you enter a custom value on our dashboard that looks like a number or a boolean, it'll be interpreted that way. The iOS SDK is strongly typed, so be aware of this distinction.

Custom attributes are one of the most powerful features of LaunchDarkly. They let you target users according to any data that you want to send to us-- organizations, groups, account plans-- anything you pass to us becomes available instantly on our dashboard.

Anonymous users

You can also distinguish logged-in users from anonymous users in the SDK, as follows:

LDUserBuilder *user = [[LDUserBuilder alloc] init];

user = [user withKey:"aa0ceb"];
user = [user withAnonymous:TRUE];
var user = LDUserBuilder()
user = user.withKey("aa0ceb")
user = user.withAnonymous(true)

You will still need to generate a unique key for anonymous users-- session IDs or UUIDs work best for this.

Anonymous users work just like regular users, except that they won't appear on your Users page in LaunchDarkly. You also can't search for anonymous users on your Features page, and you can't search or autocomplete by anonymous user keys. This is actually a good thing-- it keeps anonymous users from polluting your Users page!


The variation method determines whether a flag is enabled or not for a specific user. In iOS, there is a variation method for each type (e.g. boolVariation, stringVariation):

[[LDClient sharedInstance] boolVariation:@"your.feature.key" fallback:FALSE];
LDClient.sharedInstance().boolVariation("your.feature.key", fallback: false)

variation calls take the feature flag key, an LDUser, and a fallback value.

The fallback value will only be returned if an error is encountered-- for example, if the feature flag key doesn't exist or the user doesn't have a key specified.

The variation call will automatically create a user in LaunchDarkly if a user with that user key doesn't exist already. There's no need to create users ahead of time (but if you do need to, take a look at Identify).

Handling flag values on initial app launch

When LDClient is initialized for the first time at app launch, users will receive the feature flag fallback values until polling is completed for the first time.

You can use the userDidUpdate delegate method to be notified when the feature flag values have been polled and are ready to use (See Realtime UI Updates). Once the flags have been polled for the first time, the SDK will always use the latest stored flag values thereafter.


The track method allows you to record actions your users take on your site. This lets you record events that take place on your server. In LaunchDarkly, you can tie these events to goals in A/B tests. You can also attach custom JSON data to your event by passing an extra NSDictionary parameter to track. Here's a simple example:

 [[LDClient sharedInstance] track:@"Signed up" data:dict];
LDClient.sharedInstance().track("Signed up", data: dict)

Offline mode

In some situations, you might want to stop making remote calls to LaunchDarkly and switch to fallback values for your feature flags. offline lets you do this easily.

[[LDClient sharedInstance] offline];
[[LDClient sharedInstance] boolVariation:@"your.feature.key" fallback:FALSE]; // will always return the fallback value (FALSE)
LDClient.sharedInstance().boolVariation("your.feature.key", fallback: false) // will always return the fallback value (FALSE)

You can bring LaunchDarkly back online by calling online.

Airplane/Flight Mode

If a user's device is in airplane/flight mode or if they are not connected to a network, LaunchDarkly will use the latest stored flag settings in memory. If there are no previously stored flag settings, then the fallback values will be used.


Internally, the LaunchDarkly SDK keeps an event buffer for track calls. These are flushed periodically in a background thread. In some situations (for example, if you're testing out the SDK in a REPL), you may want to manually call flush to process events immediately.

[[LDClient sharedInstance] flush];

Note that the flush interval is configurable-- if you need to change the interval, you can do so via the configuration.

Real-Time Updates

LaunchDarkly manages all flags for a user context in real-time by polling flags based on a real-time event stream. When a flag is modified via the LaunchDarkly dashboard, the flag values for the current user will update almost immediately.

To accomplish real-time updates, LaunchDarkly broadcasts an event stream that is listened to by the iOS SDK. Whenever an event is performed on the dashboard, the iOS SDK is notified, and then polls for updated flag values.

To perform real-time updates in your app, your base class will need to conform to the ClientDelegate protocol. The userDidUpdate method of the protocol is called whenever a flag value is changed. If more than one class relies on LaunchDarkly’s feature flags, we recommend you post a notification in this method, in a manner similar to the following:

- (void)userDidUpdate{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"userUpdatedNotification" object:nil];
func userDidUpdate() {
 NSNotificationCenter.defaultCenter().postNotificationName("userUpdatedNotification", object: nil)

After this, you can add a notification observer to any class that needs to update the app based on the flag values. This observer will point to a selector which can then update your app accordingly.

Variation methods

Make sure to use variation methods to get new flag values instead of any locally stored variables.

Background Fetch

When the app is backgrounded, the iOS SDK does not receive real-time events. However, there is support for a background fetch to update flag values opportunistically, according to iOS standard defaults.

To allow background fetch for flags in your app, just add the following code in your AppDelegate:

-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler{
    [[NSNotificationCenter defaultCenter] postNotificationName:kLDBackgroundFetchInitiaited object:nil];
func application(application: UIApplication, performFetchWithCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) {
    NSNotificationCenter.defaultCenter().postNotificationName(kLDBackgroundFetchInitiated, object: nil)

You will also need to enable Background fetch in your Target’s capabilities.

Changing the User Context

If your app is used by multiple users on a single device, then you will want to ensure that each user has persistent and personalized flag settings. To achieve this, the SDK will store up to 5 user contexts on a single device, with support for switching between different user contexts.

You can use the updateUser method to switch user contexts:

LDUserBuilder *user = [[LDUserBuilder alloc] init];
 user = [user withKey:@"aa0ceb"];
[[LDClient sharedInstance] updateUser:user];
var user = LDUserBuilder()
user = user.withKey("aa0ceb")

iOS SDK Reference