Kotlin Multiplatform Feature Flags installation

1
Install the dependency
Required
Add the PostHog KMP SDK to your shared module's commonMain source set:
shared/build.gradle.kts
kotlin { sourceSets { commonMain.dependencies { implementation("com.posthog:posthog-kmp:0.+") } } }
0.+ resolves to the latest 0.x release. The SDK is a pre-release, so the API can change between minor versions – pin an exact version from Maven Central if you would rather upgrade deliberately. Kotlin/Wasm support requires 0.2.0 or higher.

Configure PostHog

Required

Call PostHog.setup() once, early in your app's lifecycle. The config is shared across every target – only the PostHogContext differs per platform.

Android needs the Application instance, so set PostHog up from your Application class – not from an Activity, whose onCreate re-runs on every recreation (for example, on rotation):

MyApplication.kt
import android.app.Application
import com.posthog.kmp.PostHog
import com.posthog.kmp.PostHogConfig
import com.posthog.kmp.PostHogContext

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()

        PostHog.setup(
            config = PostHogConfig(
                apiKey = "<ph_project_token>",
                host = "https://us.i.posthog.com",
            ),
            context = PostHogContext(this),
        )
    }
}

android/src/main/AndroidManifest.xml
<application android:name=".MyApplication" ...>

On iOS, use the no-argument PostHogContext():

MainViewController.kt
import com.posthog.kmp.PostHog
import com.posthog.kmp.PostHogConfig
import com.posthog.kmp.PostHogContext

fun MainViewController() = ComposeUIViewController {
    LaunchedEffect(Unit) {
        PostHog.setup(
            config = PostHogConfig(
                apiKey = "<ph_project_token>",
                host = "https://us.i.posthog.com",
            ),
            context = PostHogContext(),
        )
    }
    App()
}

On the web (Kotlin/JS and Kotlin/Wasm), use the no-argument PostHogContext():

main.kt
import com.posthog.kmp.PostHog
import com.posthog.kmp.PostHogConfig
import com.posthog.kmp.PostHogContext

fun main() {
    PostHog.setup(
        config = PostHogConfig(
            apiKey = "<ph_project_token>",
            host = "https://us.i.posthog.com",
        ),
        context = PostHogContext(),
    )
}

On the JVM – for example, a Compose Multiplatform desktop app – use the no-argument PostHogContext():

main.kt
import com.posthog.kmp.PostHog
import com.posthog.kmp.PostHogConfig
import com.posthog.kmp.PostHogContext

fun main() = application {
    PostHog.setup(
        config = PostHogConfig(
            apiKey = "<ph_project_token>",
            host = "https://us.i.posthog.com",
        ),
        context = PostHogContext(),
    )
    // ...
}

Send events

Recommended

Once installed, PostHog automatically captures app lifecycle events on Android and iOS. Send an event manually from shared code to test your integration:

Kotlin
import com.posthog.kmp.PostHog

PostHog.capture(
    event = "button_clicked",
    properties = mapOf(
        "button_name" to "signup"
    )
)

Evaluate boolean feature flags

Required

Flags are preloaded on setup, so this call is synchronous:

Kotlin
if (PostHog.isFeatureEnabled("flag-key")) {
    // Do something differently for this user
    // Optional: fetch the payload
    val payload = PostHog.getFeatureFlagResult("flag-key")?.getPayloadAs<Map<String, Any>>()
}

Evaluate multivariate feature flags

Optional

For multivariate flags, check which variant the user has been assigned:

Kotlin
when (PostHog.getFeatureFlag("flag-key")) {
    "control" -> showOriginalPricing()
    "variant-key" -> showNewPricing()
}

Reload flags after identifying

Optional

Flags are fetched on setup and cached. If a user's properties change – for example, after identify – reload them so they reflect the latest state:

Kotlin
PostHog.reloadFeatureFlags {
    // flags are now up to date
}

7
Running experiments
Optional
Experiments run on top of our feature flags. Once you've implemented the flag in your code, you run an experiment by creating a new experiment in the PostHog dashboard.

Next steps

Recommended

Now that you're evaluating flags, continue with the resources below to learn what else Feature Flags enables within the PostHog platform.

Resource	Description
Creating a feature flag	How to create a feature flag in PostHog
Adding feature flag code	How to check flags in your code for all platforms
Framework-specific guides	Setup guides for React Native, Next.js, Flutter, and other frameworks
How to do a phased rollout	Gradually roll out features to minimize risk
More tutorials	Other real-world examples and use cases

Kotlin Multiplatform Feature Flags installation

Install the dependency