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How to run A/B tests in Android with PostHog

Nov 22, 2023

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A/B tests enables you to compare the impact of your changes on key metrics.

PostHog makes A/B testing on Android simple. To show you how, this tutorial will guide you on how to run an A/B test with PostHog on an app built with Kotlin and Jetpack Compose. We will create a simple A/B test to see how the background color of a screen affects the click-through rate of a button.

Creating a new Android app

Our app will have two screens:

  • The first screen will have a button which will take you to a second screen.
  • The second screen will either have a red or green background color depending on if the user is in the control or test group of the A/B test. It will also have a button which captures an event when pressed. We'll use this event as our goal metric for our test.

The first step is to create a new app. Open Android Studio and create a new project. Select Empty Activity, name your project My-AB-Test, and use the defaults for everything else.

Then, replace your code in MainActivity.kt to set up a basic UI with a button to navigate to a new screen.

Kotlin
package com.example.my_ab_test


import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material3.Button
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Surface
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.runtime.mutableStateOf
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.navigation.NavController
import androidx.navigation.compose.NavHost
import androidx.navigation.compose.composable
import androidx.navigation.compose.rememberNavController
import com.example.my_ab_test.ui.theme.MyABTestTheme


class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyABTestTheme {
                Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
                    MyApp()
                }
            }
        }
    }
}


@Composable
fun MyApp() {
    val navController = rememberNavController()
    NavHost(navController = navController, startDestination = "main_screen") {
        composable("main_screen") {
            Greeting("Android", navController)
        }
        composable("second_screen") {
            SecondScreen()
        }
    }
}


@Composable
fun Greeting(name: String, navController: NavController, modifier: Modifier = Modifier) {
    Column(modifier = modifier.fillMaxSize()) {
        Text(text = "Hello $name!")
        Button(onClick = { navController.navigate("second_screen") }) {
            Text("Go to next screen")
        }
    }
}


@Composable
fun SecondScreen() {
    val isTestVariant = remember { mutableStateOf(false) } // We'll set this value later in the tutorial
    val backgroundColor = if (isTestVariant.value) Color.Green else Color.Red


    Surface(modifier = Modifier.fillMaxSize(), color = backgroundColor) {
        Column(modifier = Modifier.fillMaxSize(), horizontalAlignment = Alignment.CenterHorizontally, verticalArrangement = Arrangement.Center) {
            Button(onClick = { /* Do nothing for now */ }) {
                Text("Click Me!")
            }
        }
    }
}


@Preview(showBackground = true)
@Composable
fun DefaultPreview() {
    MyABTestTheme {
        MyApp()
    }
}

Make sure to add implementation("androidx.navigation:navigation-compose:2.4.0") to your dependencies in to app/build.gradle.kts and sync your project with the Gradle files.

Our basic set up is now complete. Build and run your app to test that it's working.

Adding PostHog to your Android app

First, add the PostHog Android SDK as a dependency in your app/build.gradle.kts file. You can find the latest version on our GitHub. For this tutorial, we use version 2.0.3.

Kotlin
dependencies {
    implementation("com.posthog.android:posthog:2.0.3")
    //... other dependencies
}

Sync your project with your Gradle file changes.

Next, we create a Kotlin class where we can configure our PostHog instance. In the src/main/java/com.example.my_ab_test folder, add a new file MyABTestApplication.kt, add the following code:

Kotlin
// in MyABTestApplication.kt
package com.example.my_ab_test


import android.app.Application
import com.posthog.android.PostHog


class MyABTestApplication : Application() {
    companion object {
        private const val POSTHOG_API_KEY = "<ph_project_api_key>"
        private const val POSTHOG_HOST = "<ph_instance_address>"
    }


    override fun onCreate() {
        super.onCreate()


        // Initialize PostHog
        val posthog = PostHog.Builder(this, POSTHOG_API_KEY, POSTHOG_HOST)
            .captureApplicationLifecycleEvents()
            .recordScreenViews()
            .build()


        // Set the initialized instance as a globally accessible instance
        PostHog.setSingletonInstance(posthog)
    }
}

To get your PostHog API key and host, sign up to PostHog. Then, you can find your API key and host in your project settings.

We now need to register our custom application class. Go to AndroidManifest.xml and add android:name=".MyABTestApplication" within the <application tag. We also need to give our app internet permission by adding <uses-permission android:name="android.permission.INTERNET" />.

Together both of these changes look like this:

XML
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">


    <uses-permission android:name="android.permission.INTERNET" />


    <application
        android:name=".MyABTestApplication"
        ...
    </application>
</manifest>

Finally, we capture a custom event when the button on SecondScreen is clicked. We'll use this event as our goal metric in our A/B test.

Update the SecondScreen function in MainActivity.kt to the following:

Kotlin
// in MainActivity.kt


import com.posthog.android.PostHog
import androidx.compose.ui.platform.LocalContext
// ... [Rest of your imports and MainActivity code]


@Composable
fun SecondScreen() {
    val isTestVariant = remember { mutableStateOf(false) } // We'll set this value later in the tutorial
    val backgroundColor = if (isTestVariant.value) Color.Green else Color.Red


    val context = LocalContext.current // new


    Surface(modifier = Modifier.fillMaxSize(), color = backgroundColor) {
        Column(modifier = Modifier.fillMaxSize(), horizontalAlignment = Alignment.CenterHorizontally, verticalArrangement = Arrangement.Center) {
            Button(onClick = {
                PostHog.with(context)
                    .capture("feature_button_clicked");
            }) {
                Text("Click Me!")
            }
        }
    }
}

To check your setup, build and run your app. Click your button a few times and you should start seeing events in the PostHog event explorer.

Android events captured

Create an A/B test in PostHog

The next step is to set up an A/B test (we call them experiments in PostHog).

Go to the Experiments tab in PostHog and click "New experiment". Add the following details to your experiment:

  1. Name it "Android background color experiment".
  2. Set "Feature flag key" to android-background-color-experiment.
  3. Under the experiment goal, select the feature_button_clicked we created in the previous step.
  4. Use the default values for all other fields.

Click "Save as draft" and then click "Launch".

Experiment setup in PostHog

Implement the A/B test code

The final step is to add the experiment code that does the following:

  1. Retrieve the value of the android-background-color-experiment flag when SecondScreen is initialized.
  2. Change the background color of SecondScreen based on the value of the flag (control or test).

To do this, update the code in MainActivity.kt with the following:

Kotlin
// in MainActivity.kt


import androidx.compose.runtime.LaunchedEffect
// ... [Rest of your imports and MainActivity code]




@Composable
fun SecondScreen() {
    val context = LocalContext.current
    val isTestVariant = remember { mutableStateOf(false) }


    // LaunchedEffect to call PostHog.getFeatureFlag() once when the composable is initialized
    LaunchedEffect(key1 = Unit) {
        isTestVariant.value = PostHog.with(context).getFeatureFlag("android-background-color-experiment") == "test"
    }


    val backgroundColor = if (isTestVariant.value) Color.Green else Color.Red


    Surface(modifier = Modifier.fillMaxSize(), color = backgroundColor) {
        // ... [rest of SecondScreen code remains unchanged]
    }
}


// ... [rest of the file remains unchanged]

That's it! Your A/B test is now ready. When you run your app, you see either green or red as the background color of SecondScreen and PostHog will capture button clicks for each variant to calculate if changing the color has a statistically significant impact.

If you want to test both variants of your experiment to make sure they are working correctly, you can add an optional override to your feature flag.

Lastly, you can view your test results on the experiment page.

Further reading