allow optional reuse of anonymous id

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Next
 
+- feat: support reuse of `anonymousId` between user changes ([#229](https://github.com/PostHog/posthog-android/pull/229))
+
 ## 3.11.3 - 2025-02-26
 
 - feat: support quota limiting for feature flags ([#228](https://github.com/PostHog/posthog-android/pull/228) and [#230](https://github.com/PostHog/posthog-android/pull/230))

posthog-samples/posthog-android-sample/lint-baseline.xml

@@ -1,17 +1,61 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<issues format="6" by="lint 8.1.3" type="baseline" client="gradle" dependencies="false" name="AGP (8.1.3)" variant="all" version="8.1.3">
+<issues format="6" by="lint 8.2.2" type="baseline" client="gradle" dependencies="false" name="AGP (8.2.2)" variant="all" version="8.2.2">
 
     <issue
         id="GradleDependency"
-        message="A newer version of androidx.activity:activity-compose than 1.8.0 is available: 1.8.2"
-        errorLine1="    implementation(&quot;androidx.activity:activity-compose:1.8.0&quot;)"
+        message="A newer version of androidx.activity:activity-compose than 1.7.2 is available: 1.10.0"
+        errorLine1="    implementation(&quot;androidx.activity:activity-compose:1.7.2&quot;)"
         errorLine2="                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~">
         <location
             file="build.gradle.kts"
-            line="76"
+            line="77"
             column="21"/>
     </issue>
 
+    <issue
+        id="GradleDependency"
+        message="A newer version of com.squareup.leakcanary:leakcanary-android than 2.12 is available: 2.14"
+        errorLine1="    debugImplementation(&quot;com.squareup.leakcanary:leakcanary-android:2.12&quot;)"
+        errorLine2="                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~">
+        <location
+            file="build.gradle.kts"
+            line="87"
+            column="26"/>
+    </issue>
+
+    <issue
+        id="ComposableNaming"
+        message="Composable functions that return Unit should start with an uppercase letter"
+        errorLine1="fun greeting("
+        errorLine2="    ~~~~~~~~">
+        <location
+            file="src/main/java/com/posthog/android/sample/MainActivity.kt"
+            line="42"
+            column="5"/>
+    </issue>
+
+    <issue
+        id="ComposableNaming"
+        message="Composable functions that return Unit should start with an uppercase letter"
+        errorLine1="fun greetingPreview() {"
+        errorLine2="    ~~~~~~~~~~~~~~~">
+        <location
+            file="src/main/java/com/posthog/android/sample/MainActivity.kt"
+            line="59"
+            column="5"/>
+    </issue>
+
+    <issue
+        id="ComposableNaming"
+        message="Composable functions that return Unit should start with an uppercase letter"
+        errorLine1="fun postHogAndroidSampleTheme("
+        errorLine2="    ~~~~~~~~~~~~~~~~~~~~~~~~~">
+        <location
+            file="src/main/java/com/posthog/android/sample/ui/theme/Theme.kt"
+            line="42"
+            column="5"/>
+    </issue>
+
     <issue
         id="UnusedResources"
         message="The resource `R.drawable.android_logo` appears to be unused">
@@ -26,7 +70,7 @@
         errorLine2="                  ~~~~~~~~~~~~~~~~~">
         <location
             file="src/main/res/values/strings.xml"
-            line="4"
+            line="5"
             column="19"/>
     </issue>
 
@@ -37,14 +81,47 @@
             file="src/main/res/drawable/android_logo.png"/>
     </issue>
 
+    <issue
+        id="Autofill"
+        message="Missing `autofillHints` attribute"
+        errorLine1="    &lt;EditText"
+        errorLine2="     ~~~~~~~~">
+        <location
+            file="src/main/res/layout/normal_activity.xml"
+            line="49"
+            column="6"/>
+    </issue>
+
+    <issue
+        id="LabelFor"
+        message="Missing accessibility label: provide either a view with an `android:labelFor` that references this view or provide an `android:hint`"
+        errorLine1="    &lt;EditText"
+        errorLine2="     ~~~~~~~~">
+        <location
+            file="src/main/res/layout/normal_activity.xml"
+            line="49"
+            column="6"/>
+    </issue>
+
+    <issue
+        id="HardcodedText"
+        message="Hardcoded string &quot;Button text&quot;, should use `@string` resource"
+        errorLine1="        android:text=&quot;Button text&quot;"
+        errorLine2="        ~~~~~~~~~~~~~~~~~~~~~~~~~~">
+        <location
+            file="src/main/res/layout/normal_activity.xml"
+            line="39"
+            column="9"/>
+    </issue>
+
     <issue
         id="HardcodedText"
-        message="Hardcoded string &quot;Text&quot;, should use `@string` resource"
-        errorLine1="        android:text=&quot;Text&quot;"
-        errorLine2="        ~~~~~~~~~~~~~~~~~~~">
+        message="Hardcoded string &quot;EditText text&quot;, should use `@string` resource"
+        errorLine1="        android:text=&quot;EditText text&quot;"
+        errorLine2="        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~">
         <location
-            file="src/main/res/layout/nothing_activity.xml"
-            line="14"
+            file="src/main/res/layout/normal_activity.xml"
+            line="52"
             column="9"/>
     </issue>
 

posthog/api/posthog.api

@@ -72,8 +72,8 @@ public final class com/posthog/PostHog$Companion : com/posthog/PostHogInterface
 public class com/posthog/PostHogConfig {
 	public static final field Companion Lcom/posthog/PostHogConfig$Companion;
 	public static final field DEFAULT_HOST Ljava/lang/String;
-	public fun <init> (Ljava/lang/String;Ljava/lang/String;ZZZZIIIILcom/posthog/PostHogEncryption;Lcom/posthog/PostHogOnFeatureFlags;ZLcom/posthog/PostHogPropertiesSanitizer;Lkotlin/jvm/functions/Function1;Lcom/posthog/PersonProfiles;)V
-	public synthetic fun <init> (Ljava/lang/String;Ljava/lang/String;ZZZZIIIILcom/posthog/PostHogEncryption;Lcom/posthog/PostHogOnFeatureFlags;ZLcom/posthog/PostHogPropertiesSanitizer;Lkotlin/jvm/functions/Function1;Lcom/posthog/PersonProfiles;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public fun <init> (Ljava/lang/String;Ljava/lang/String;ZZZZIIIILcom/posthog/PostHogEncryption;Lcom/posthog/PostHogOnFeatureFlags;ZLcom/posthog/PostHogPropertiesSanitizer;Lkotlin/jvm/functions/Function1;ZLcom/posthog/PersonProfiles;)V
+	public synthetic fun <init> (Ljava/lang/String;Ljava/lang/String;ZZZZIIIILcom/posthog/PostHogEncryption;Lcom/posthog/PostHogOnFeatureFlags;ZLcom/posthog/PostHogPropertiesSanitizer;Lkotlin/jvm/functions/Function1;ZLcom/posthog/PersonProfiles;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun addIntegration (Lcom/posthog/PostHogIntegration;)V
 	public final fun getApiKey ()Ljava/lang/String;
 	public final fun getCachePreferences ()Lcom/posthog/internal/PostHogPreferences;
@@ -97,6 +97,7 @@ public class com/posthog/PostHogConfig {
 	public final fun getPreloadFeatureFlags ()Z
 	public final fun getPropertiesSanitizer ()Lcom/posthog/PostHogPropertiesSanitizer;
 	public final fun getReplayStoragePrefix ()Ljava/lang/String;
+	public final fun getReuseAnonymousId ()Z
 	public final fun getSdkName ()Ljava/lang/String;
 	public final fun getSdkVersion ()Ljava/lang/String;
 	public final fun getSendFeatureFlagEvent ()Z
@@ -124,6 +125,7 @@ public class com/posthog/PostHogConfig {
 	public final fun setPreloadFeatureFlags (Z)V
 	public final fun setPropertiesSanitizer (Lcom/posthog/PostHogPropertiesSanitizer;)V
 	public final fun setReplayStoragePrefix (Ljava/lang/String;)V
+	public final fun setReuseAnonymousId (Z)V
 	public final fun setSdkName (Ljava/lang/String;)V
 	public final fun setSdkVersion (Ljava/lang/String;)V
 	public final fun setSendFeatureFlagEvent (Z)V

posthog/src/main/java/com/posthog/PostHog.kt

@@ -549,11 +549,14 @@ public class PostHog private constructor(
         val previousDistinctId = this.distinctId
 
         val props = mutableMapOf<String, Any>()
-        val anonymousId = this.anonymousId
-        if (anonymousId.isNotBlank()) {
-            props["\$anon_distinct_id"] = anonymousId
-        } else {
-            config?.logger?.log("identify called with invalid anonymousId: $anonymousId.")
+
+        if (config?.reuseAnonymousId != true) {
+            val anonymousId = this.anonymousId
+            if (anonymousId.isNotBlank()) {
+                props["\$anon_distinct_id"] = anonymousId
+            } else {
+                config?.logger?.log("identify called with invalid anonymousId: $anonymousId.")
+            }
         }
 
         val hasDifferentDistinctId = previousDistinctId != distinctId
@@ -572,11 +575,13 @@ public class PostHog private constructor(
                 userPropertiesSetOnce = userPropertiesSetOnce,
             )
 
-            // We keep the AnonymousId to be used by decide calls and identify to link the previousId
-            if (previousDistinctId.isNotBlank()) {
-                this.anonymousId = previousDistinctId
-            } else {
-                config?.logger?.log("identify called with invalid former distinctId: $previousDistinctId.")
+            if (config?.reuseAnonymousId != true) {
+                // We keep the AnonymousId to be used by decide calls and identify to link the previousId
+                if (previousDistinctId.isNotBlank()) {
+                    this.anonymousId = previousDistinctId
+                } else {
+                    config?.logger?.log("identify called with invalid former distinctId: $previousDistinctId.")
+                }
             }
             this.distinctId = distinctId
 
@@ -686,7 +691,11 @@ public class PostHog private constructor(
         val groups = getPreferences().getValue(GROUPS) as? Map<String, String>
 
         val distinctId = this.distinctId
-        val anonymousId = this.anonymousId
+        var anonymousId: String? = null
+
+        if (config?.reuseAnonymousId != true) {
+            anonymousId = this.anonymousId
+        }
 
         if (distinctId.isBlank()) {
             config?.logger?.log("Feature flags not loaded, distinctId is invalid: $distinctId")
@@ -774,8 +783,13 @@ public class PostHog private constructor(
 
         // only remove properties, preserve BUILD and VERSION keys in order to to fix over-sending
         // of 'Application Installed' events and under-sending of 'Application Updated' events
-        val except = listOf(VERSION, BUILD)
-        getPreferences().clear(except = except)
+        val except = mutableListOf(VERSION, BUILD)
+        // preserve the ANONYMOUS_ID if reuseAnonymousId is enabled (for preserving a guest user
+        // account on the device)
+        if (config?.reuseAnonymousId == true) {
+            except.add(ANONYMOUS_ID)
+        }
+        getPreferences().clear(except = except.toList())
         featureFlags?.clear()
         featureFlagsCalled.clear()
         synchronized(identifiedLock) {

posthog/src/main/java/com/posthog/PostHogConfig.kt

@@ -101,6 +101,30 @@ public open class PostHogConfig(
      * generating anonymous id (which as of now is just random UUID v7)
      */
     public var getAnonymousId: ((UUID) -> UUID) = { it },
+    /**
+     * Flag to reuse the anonymous id.
+     * If enabled, the anonymous id will be reused across `identify()` and `reset()` calls.
+     *
+     * Events captured before the user has identified won't be linked to the identified user, e.g.:
+     *
+     * Guest user (anonymous id) captures an event (click on X).
+     *
+     * User logs in (User A) calls identify
+     * User A captures an event (clicks on Y)
+     * User A logs out (calls reset)
+     *
+     * Guest user (reused anonymous id) captures an event (click on Z)
+     *
+     * click on X and click on Z events will be associated to the same user (anonymous id)
+     *
+     * clicks on Y event will be associated only with User A
+     *
+     * This will allow you to reuse the anonymous id as a Guest user, but all the events happening before
+     * or after the user logs in and logs out won't be associated.
+     *
+     * Defaults to false.
+     */
+    public var reuseAnonymousId: Boolean = false,
     /**
      * Determines the behavior for processing user profiles.
      * - `ALWAYS`: We will process persons data for all events.

posthog/src/test/java/com/posthog/PostHogTest.kt

@@ -44,6 +44,7 @@ internal class PostHogTest {
         preloadFeatureFlags: Boolean = true,
         reloadFeatureFlags: Boolean = true,
         sendFeatureFlagEvent: Boolean = true,
+        reuseAnonymousId: Boolean = false,
         integration: PostHogIntegration? = null,
         cachePreferences: PostHogMemoryPreferences = PostHogMemoryPreferences(),
         propertiesSanitizer: PostHogPropertiesSanitizer? = null,
@@ -59,6 +60,7 @@ internal class PostHogTest {
                     addIntegration(integration)
                 }
                 this.sendFeatureFlagEvent = sendFeatureFlagEvent
+                this.reuseAnonymousId = reuseAnonymousId
                 this.cachePreferences = cachePreferences
                 this.propertiesSanitizer = propertiesSanitizer
             }
@@ -1036,6 +1038,60 @@ internal class PostHogTest {
         assertEquals("myNewDistinctId", sut.distinctId())
     }
 
+    @Test
+    fun `reuse anonymousId when flag reuseAnonymousId is true`() {
+        val http = mockHttp()
+        val url = http.url("/")
+
+        val sut = getSut(url.toString(), preloadFeatureFlags = false, reloadFeatureFlags = false, reuseAnonymousId = true)
+
+        val anonymousId = sut.distinctId()
+        sut.reset()
+
+        queueExecutor.shutdownAndAwaitTermination()
+
+        assertEquals(anonymousId, sut.distinctId())
+    }
+
+    @Test
+    fun `anonymousId is not overwritten on re-identify when reuseAnonymousId is true`() {
+        val http = mockHttp()
+        val url = http.url("/")
+
+        val sut = getSut(url.toString(), preloadFeatureFlags = false, reloadFeatureFlags = false, reuseAnonymousId = true)
+
+        val anonymousId = sut.distinctId()
+        sut.identify("myDistinctId")
+        sut.identify("myNewDistinctId")
+        sut.reset()
+
+        queueExecutor.shutdownAndAwaitTermination()
+
+        assertEquals(anonymousId, sut.distinctId())
+    }
+
+    @Test
+    fun `do not link anonymousId on identify when reuseAnonymousId is true`() {
+        val http = mockHttp()
+        val url = http.url("/")
+
+        val sut = getSut(url.toString(), preloadFeatureFlags = false, reloadFeatureFlags = false, reuseAnonymousId = true)
+
+        sut.identify("myDistinctId")
+
+        queueExecutor.shutdownAndAwaitTermination()
+
+        val request = http.takeRequest()
+
+        assertEquals(1, http.requestCount)
+        val content = request.body.unGzip()
+        val batch = serializer.deserialize<PostHogBatchEvent>(content.reader())
+
+        val theEvent = batch.batch.first()
+
+        assertNull(theEvent.properties!!["\$anon_distinct_id"])
+    }
+
     @Test
     fun `do not send feature flags called event twice`() {
         val file = File("src/test/resources/json/basic-decide-no-errors.json")