Push-Benachrichtigungen mit Cloud Messaging

Was ist Cloud Messaging?

Die Messaging-Abhängigkeit hinzufügen

// app/build.gradle.kts
dependencies {
    implementation(platform("com.google.firebase:firebase-bom:33.1.0"))
    implementation("com.google.firebase:firebase-messaging")
}

Die Benachrichtigungsberechtigung

<!-- AndroidManifest.xml -->
<uses-permission android:name="android.permission.POST_NOTIFICATIONS" />

Die Berechtigung anfordern

import android.Manifest
import android.os.Build
import androidx.activity.result.contract.ActivityResultContracts

val requestPermission = registerForActivityResult(
    ActivityResultContracts.RequestPermission()
) { granted ->
    println(if (granted) "Notifications allowed" else "Notifications denied")
}

fun askNotificationPermission() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
        requestPermission.launch(Manifest.permission.POST_NOTIFICATIONS)
    }
}

Das Registrierungstoken

import com.google.firebase.Firebase
import com.google.firebase.messaging.messaging
import kotlinx.coroutines.tasks.await

suspend fun currentToken(): String {
    return Firebase.messaging.token.await()
}

Der Messaging-Service

import com.google.firebase.messaging.FirebaseMessagingService
import com.google.firebase.messaging.RemoteMessage

class MyFcmService : FirebaseMessagingService() {

    override fun onNewToken(token: String) {
        // Upload the fresh token to your backend
        sendTokenToServer(token)
    }

    override fun onMessageReceived(message: RemoteMessage) {
        val title = message.notification?.title ?: "New message"
        val body = message.notification?.body ?: ""
        showNotification(title, body)
    }

    private fun sendTokenToServer(token: String) { /* ... */ }
    private fun showNotification(title: String, body: String) { /* ... */ }
}

Den Service registrieren

<!-- AndroidManifest.xml inside <application> -->
<service
    android:name=".MyFcmService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

Benachrichtigungs- und Datennachrichten

import com.google.firebase.messaging.RemoteMessage

fun handle(message: RemoteMessage) {
    val type = message.data["type"]      // your custom field
    val itemId = message.data["itemId"]
    when (type) {
        "chat" -> openChat(itemId)
        "promo" -> openPromo(itemId)
    }
}
fun openChat(id: String?) {}
fun openPromo(id: String?) {}

Einen Benachrichtigungskanal erstellen

import android.app.NotificationChannel
import android.app.NotificationManager
import android.content.Context

fun createChannel(context: Context) {
    val channel = NotificationChannel(
        "messages",
        "Messages",
        NotificationManager.IMPORTANCE_HIGH
    )
    val manager = context.getSystemService(NotificationManager::class.java)
    manager.createNotificationChannel(channel)
}

Die Benachrichtigung anzeigen

import android.content.Context
import androidx.core.app.NotificationCompat
import androidx.core.app.NotificationManagerCompat

fun showNotification(context: Context, title: String, body: String) {
    val notification = NotificationCompat.Builder(context, "messages")
        .setSmallIcon(android.R.drawable.ic_dialog_info)
        .setContentTitle(title)
        .setContentText(body)
        .setAutoCancel(true)
        .build()

    NotificationManagerCompat.from(context).notify(1, notification)
}

Topic-Abonnements

import com.google.firebase.Firebase
import com.google.firebase.messaging.messaging
import kotlinx.coroutines.tasks.await

suspend fun subscribeToNews() {
    Firebase.messaging.subscribeToTopic("news").await()
}

suspend fun unsubscribeFromNews() {
    Firebase.messaging.unsubscribeFromTopic("news").await()
}

Kurze Überprüfung

Zusammenfassung: Cloud Messaging