In-App Messages in Mobile App

Implementing In-App Messages in Mobile Apps

In-App Messages — these are not push notifications. They display only when the app is open, don't require permissions, don't go to notification center. A modal window on app launch, a banner at the bottom when needed, fullscreen offer after first purchase — all of this is IAM. The main technical task: show them at the right moment without annoying the user.

Platform Solutions vs Custom Implementation

Two paths: use an SDK (OneSignal IAM, Firebase In-App Messaging, Braze, Intercom, Appcues) or implement your own mechanism. SDK — quick start but limited UI customization. Custom solution — full control over appearance and display logic.

Firebase In-App Messaging — free, integrates with Firebase Analytics events:

// iOS — automatically shows IAM when logging specified event
Analytics.logEvent("checkout_started", parameters: [
    "cart_value": 450.0
])
// In Firebase Console: IAM trigger = event "checkout_started", condition cart_value > 200

// Android
FirebaseAnalytics.getInstance(context).logEvent("checkout_started") {
    param("cart_value", 450.0)
}

Firebase IAM shows message automatically — the app doesn't need to do anything else. Limitation: UI is only edited through Firebase Console (templates), no full control over animations and styles.

Custom Implementation: Architecture

For full control, implement your own IAM engine. Components:

1. Campaign Manager — fetches list of active campaigns from backend (or Remote Config).
2. Trigger Engine — tracks app events, matches with campaign conditions.
3. Display Controller — manages display queue, anti-spam rules.
4. UI Layer — renders specific message type.

// Android — Display Controller
class InAppMessageController(
    private val campaignRepo: CampaignRepository,
    private val displayHistory: DisplayHistoryDao
) {
    suspend fun onEvent(eventName: String, params: Map<String, Any> = emptyMap()) {
        val campaigns = campaignRepo.getActiveCampaigns()
        val eligible = campaigns.filter { campaign ->
            campaign.trigger.eventName == eventName &&
            matchesConditions(campaign, params) &&
            !wasShownRecently(campaign.id)
        }

        // Show only one message at a time — priority by score
        eligible.maxByOrNull { it.priority }?.let { campaign ->
            displayHistory.record(campaign.id, System.currentTimeMillis())
            showMessage(campaign)
        }
    }

    private suspend fun wasShownRecently(campaignId: String): Boolean {
        val lastShown = displayHistory.getLastShownTime(campaignId) ?: return false
        val cooldownMs = 24 * 60 * 60 * 1000L // 24 hours
        return System.currentTimeMillis() - lastShown < cooldownMs
    }
}

UI Types and How to Display Them

Modal (central popup). On iOS — through UIViewController with modalPresentationStyle = .overCurrentContext and transparent background:

let iamVC = InAppMessageViewController(campaign: campaign)
iamVC.modalPresentationStyle = .overCurrentContext
iamVC.modalTransitionStyle = .crossDissolve
topViewController?.present(iamVC, animated: true)

Finding topViewController in complex navigation (TabBar + NavigationController + modals) — a separate task. Recursive helper through presentedViewController and children.

Bottom Sheet / Banner. On Android — BottomSheetDialogFragment or custom View added through WindowManager over current content. Second option works even in fragments without knowing the current screen, but requires SYSTEM_ALERT_WINDOW permission — undesirable.

Better — BottomSheet through supportFragmentManager:

class InAppBottomSheet : BottomSheetDialogFragment() {
    // ... campaign data binding
    override fun onCreateView(...) = InAppBottomSheetBinding.inflate(inflater).also {
        binding = it
    }.root
}

InAppBottomSheet.newInstance(campaign).show(supportFragmentManager, "iam_bottom_sheet")

Fullscreen. Separate Activity with FLAG_FULLSCREEN — most reliable on Android. On iOS — UIViewController with modalPresentationStyle = .fullScreen.

Targeting and Display Conditions

Without frequency cap, IAM becomes annoying. Store last shown time of each campaign — in Room (Android) or Core Data / UserDefaults (iOS, if data is small).

Analytics

Minimal set of events for IAM analytics:

• iam_displayed — message shown
• iam_dismissed — closed without action
• iam_action_clicked — action button clicked (with action_id)
• iam_converted — target event after display (purchase, signup)

Analytics.logEvent("iam_action_clicked", parameters: [
    "campaign_id": campaign.id,
    "action_id": "upgrade_now",
    "screen": currentScreenName
])

Timeframe

Firebase IAM integration with event triggers — 2–3 days. Custom IAM engine with Campaign Manager, Trigger Engine, three UI types (modal, banner, fullscreen), analytics and frequency caps — 10–15 working days.