Android Notification Channel — Complete Guide

// No channel — notification won't show on API 26+
val builder = NotificationCompat.Builder(this, "general")
    .setContentTitle("Hello")
    .setContentText("World")
    .setSmallIcon(R.drawable.ic_notification)

// Channel created but wrong importance
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    val channel = NotificationChannel(
        "alerts", "Alerts", NotificationManager.IMPORTANCE_MIN // No sound!
    )
    notificationManager.createNotificationChannel(channel)
}

class App : Application() {
    override fun onCreate() {
        super.onCreate()
        createNotificationChannels()
    }

    private fun createNotificationChannels() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val notificationManager = getSystemService(NotificationManager::class.java)

            // High importance — makes sound, shows heads-up
            val urgentChannel = NotificationChannel(
                URGENT_CHANNEL_ID,
                "Urgent Alerts",
                NotificationManager.IMPORTANCE_HIGH
            ).apply {
                description = "Time-sensitive notifications"
                enableVibration(true)
                setLightColor(Color.RED)
            }

            // Default importance — shows in shade, no sound
            val defaultChannel = NotificationChannel(
                DEFAULT_CHANNEL_ID,
                "Notifications",
                NotificationManager.IMPORTANCE_DEFAULT
            ).apply {
                description = "General notifications"
            }

            // Low importance — no sound, no heads-up
            val silentChannel = NotificationChannel(
                SILENT_CHANNEL_ID,
                "Silent Updates",
                NotificationManager.IMPORTANCE_LOW
            ).apply {
                description = "Updates without interruption"
                setSound(null, null)
            }

            // Create channel group
            val group = NotificationChannelGroup("social", "Social")
            notificationManager.createNotificationChannelGroup(group)

            notificationManager.createNotificationChannels(
                listOf(urgentChannel, defaultChannel, silentChannel)
            )
        }
    }
}