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# Kotlin Multiplatform Feature Flags installation

1.  1

    ## Install the dependency

    Required

    Add the PostHog KMP SDK to your shared module's `commonMain` source set:

    shared/build.gradle.kts

    ```kotlin
    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](https://central.sonatype.com/artifact/com.posthog/posthog-kmp) if you would rather upgrade deliberately. Kotlin/Wasm support requires `0.2.0` or higher.

2.  2

    ## 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.

    ## Tab

    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

    ```kotlin
    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),
            )
        }
    }
    ```

    Register the class in your `AndroidManifest.xml`:

    android/src/main/AndroidManifest.xml

    ```xml
    <application android:name=".MyApplication" ...>
    ```

    ## Tab

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

    MainViewController.kt

    ```kotlin
    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()
    }
    ```

    ## Tab

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

    main.kt

    ```kotlin
    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(),
        )
    }
    ```

    ## Tab

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

    main.kt

    ```kotlin
    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(),
        )
        // ...
    }
    ```

3.  3

    ## 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

    ```kotlin
    import com.posthog.kmp.PostHog
    
    PostHog.capture(
        event = "button_clicked",
        properties = mapOf(
            "button_name" to "signup"
        )
    )
    ```

4.  4

    ## Evaluate boolean feature flags

    Required

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

    Kotlin

    ```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>>()
    }
    ```

5.  5

    ## Evaluate multivariate feature flags

    Optional

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

    Kotlin

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

6.  6

    ## 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

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

7.  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.

8.  8

    ## 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](/docs/feature-flags/creating-feature-flags.md) | How to create a feature flag in PostHog |
    | [Adding feature flag code](/docs/feature-flags/adding-feature-flag-code.md) | How to check flags in your code for all platforms |
    | [Framework-specific guides](/docs/feature-flags/tutorials.md#framework-guides) | Setup guides for React Native, Next.js, Flutter, and other frameworks |
    | [How to do a phased rollout](/tutorials/phased-rollout.md) | Gradually roll out features to minimize risk |
    | [More tutorials](/docs/feature-flags/tutorials.md) | Other real-world examples and use cases |

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