This is demo app to implement FCM On Device Push Notification Scheduling using AlarmManager and WorkManager.

• We can use Cloud Pub/Sub with Firebase Cloud Functions to send FCM Push Notifications. But this solution is costly to implement.
• Here, We are using regular FCM Push Notifications and scheduling it on device.

In this demo app, We are subscribing to a FCM Channel discount-offers. We'll receive Data payload from FCM to this subscribed channel and we will process and schedule it.

• Firebase Messaging - Firebase Cloud Messaging Library.
• Firebase IID - Firebase Instance ID Library.
• WorkManager - Used for Background Work Processing.

• Setup project in Firebase Console.
• Download and paste google-services.json configuration file in /app directory.
• Keep legacy API key for FCM Push Notification REST.

src
│
└───fcm
│   │   MyFirebaseMessagingService.kt
│   │   NotificationBroadcastReceiver.kt
│   │   ScheduledWorker.kt
│   
└───util
|   │   NotificationUtil.kt
|   │   SettingUtil.kt
|
└───ui
|   │   MainActivity.kt
|   

• MyFirebaseMessagingService: FCM Receiver Service Implementation. Process of Notification Scheduling using AlarmManager is implemented here.

• NotificationBroadcastReceiver: BroadcastReceiver Implementation. Executed when AlarmManager is triggered. WorkManager is initiated and executed for background processing.

• ScheduledWorker: WorkManager Implementation. Notification is displayed in the system tray and other background processed are executed.

• NotificationUtil: Implementation to display Notification on the system tray.

• SettingUtil: Function implementation to check whether Automatic Date & Time setting is ON/OFF.

• MainActivity: UI Implementation to subscribe to FCM Channel.

• Subscribe to discount-offers FCM Channel from Android Device.
• Data Payload will be as follows

 { 
    "to": "/topics/discount-offers", 
    "priority": "high",
    "data" : {
      "title" : "TITLE_HERE",
      "message" : "MESSAGE_HERE",
      "isScheduled" : "true",
      "scheduledTime" : "2019-12-13 09:41:00"
    }
}

Format of scheduledTime: YYYY-MM-DD HH:MM:SS

• Receive FCM on device and onMessageReceived() in MyFirebaseMessagingService will be invoked. In this, following operations will be done-
  • If isScheduled parameter received is false then notifications is displayed in system tray instantly.
  • If isScheduled is true then scheduledTime is parsed from payload and AlarmManager is used to set one-time alarm at that time and NotificationBroadcastReceiver implementation will be executed on that time.
  • In onReceive(), we have scheduled a WorkManager ScheduledWorker for background work processing. There in doWork(), we're finally we're displaying Notification on system tray. Do any background proessing and return status from WorkManager.

Hurrah!😍 we have successfully implemented On-Device Scheduling of FCM Push Notification👍.

I have sent below payload with to the FCM Channel (discount-offers).

{ 
 "to": "/topics/discount-offers", 
 "priority": "high",
 "data" : {
  "title" : "🎅 Christmas Offer 🎄",
  "message" : "Grab 90% Discount 😍 on Mobile Phones",
  "isScheduled" : "true",
  "scheduledTime" : "2019-12-13 14:12:00"
 }
}

🚀See output below and notice that Internet/Wi-Fi is OFF still at exactly 02:12 pm I'm getting a notification on the system tray 😃.

Yippie 😍! It's working as expected. Hope you liked that. If you find it helpful please share this. Maybe it'll help someone needy!

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MIT License

Copyright (c) 2019 Shreyas Patil

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