How Do Reminders Appear In Android App?

In this tutorial, you will be issuing Notifications to remind yourself to take care of those dearest to your heart: your pets.

Notifications are a handy way to add features and functionality to your application without your users directly interacting with them. For example, they can be used to add playback controls to a music app, provide quick actions to respond to sms or email and alert about breaking news stories among many others.

You will work with the Notification APIs to issue Notifications with the NotificationManager, schedule Alarms with the AlarmManager and enhance them by using groups, channels and actions.

Note: This tutorial assumes you have basic knowledge of Kotlin and Android. If you're new to Android, check out our Android tutorials. If you know Android, but are unfamiliar with Kotlin, take a look at Kotlin For Android: An Introduction. I also assume you have knowledge of the compatibility libraries to backport functionality to an older version of the OS.

Getting Started

Start by downloading the project materials by using the Download Materials button found at the top or bottom of this tutorial. Unzip the contents to a folder and remember the location. Open Android Studio and, at the splash page, choose Open an existing Android Studio Project, navigate to the recently downloaded folder and select PetMedicineReminder-Starter.

Once the starter project finishes loading and building, run the application on a device or emulator.

Once the app is running, load the sample data by selecting the overflow icon in the top right and tapping Load Sample Data. When the data loads, you should see a listing of reminders to administer medications to a few pets.

Android Notifications

Not super exciting but here is where you will display your first notification.

Displaying your First Notification

In order to display a notification, you will have to do some setup work. You will need to:

Create a notification channel.
Register the notification channel.
Create a notification.
Send a notification using NotificationManager.

Create a Notification Channel

Notification channels provide a common visual and auditory experience for notifications of a similar type. Since their introduction in API 26, you are now required to set a channel for a notification, otherwise they will not display on newer versions of Android.

Open the NotificationHelper.kt file under the notif directory and add the following code to the createNotificationChannel() method:

fun createNotificationChannel(context: Context, importance: Int, showBadge: Boolean, name: String, description: String) {   // 1   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {      // 2     val channelId = "${context.packageName}-$name"     val channel = NotificationChannel(channelId, name, importance)     channel.description = description     channel.setShowBadge(showBadge)      // 3     val notificationManager = context.getSystemService(NotificationManager::class.java)     notificationManager.createNotificationChannel(channel)   } }

Here you:

Safety checked the OS version for API 26 and greater.
Created a unique name for the notification channel. The name and description are displayed in the application's Notification settings.
Created the channel using the NotificationManager.

Nice work! Now you need to call this method.

Register the Notification Channel

Open the PetRx.kt application file under the root package and add the following code to the onCreate() method:

NotificationHelper.createNotificationChannel(this,     NotificationManagerCompat.IMPORTANCE_DEFAULT, false,     getString(R.string.app_name), "App notification channel.")

Now that the channel is created, you can send a notification to it when the sample data is loaded.

Create a Notification

Open the NotificationHelper.kt file and navigate to createSampleDataNotification(). Add the following code:

// 1 val channelId = "${context.packageName}-${context.getString(R.string.app_name)}" // 2 val notificationBuilder = NotificationCompat.Builder(context, channelId).apply {   setSmallIcon(R.drawable.ic_stat_medicine) // 3   setContentTitle(title) // 4   setContentText(message) // 5   setStyle(NotificationCompat.BigTextStyle().bigText(bigText)) // 6   priority = NotificationCompat.PRIORITY_DEFAULT // 7   setAutoCancel(autoCancel) // 8 }

Here you:

Create the unique channelId for this app using the package name and app name.
Use NotificationCompat.Builder to begin building the notification.
Set a small icon to be display in the notification shade. This is the only required attribute.
Set a title for the notification.
Set content for the notification.
Set the style of the notification style to NotificationCompat.BigTextStyle().
Set the notifications priority to the default priority. Priority indicates how much of the user's attention the notification should draw. You will see other usages later but acceptable values include:
- PRIORITY_MIN
- PRIORTY_MAX
- PRIORITY_LOW
- PRIORTY_HIGH
- PRIORITY_DEFAULT
Set the notification to auto cancel when tapped.

Pending Intents

So far you have created the notification channel and began building a notification but you want to direct the user somewhere when they tap on the notification. This requires adding a PendingIntent to the notification calling setContentIntent when building the notification. A PendingIntent is roughly described as an action to be taken at a later point in time.

Add the following lines to the createSampleDataNotification() method inside the apply lambda just after setAutoCancel(autoCancel):

// 1 val intent = Intent(context, MainActivity::class.java) intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK // 2 val pendingIntent = PendingIntent.getActivity(context, 0, intent, 0) // 3 setContentIntent(pendingIntent)

Here you:

Created an Intent to launch the MainActivity.
Wrapped the Intent in a PendingIntent, created through the getActivity() method which returns a description of an Activity to be launched.
Called setContentIntent() to attach it to the NotificationCompat.Builder.

Notifying the Manager

The last piece to issuing a notification is getting a reference to the NotificationManagerCompat system service and calling notify().

Add the following code after the apply lambda:

// 1 val notificationManager = NotificationManagerCompat.from(context) // 2 notificationManager.notify(1001, notificationBuilder.build())

Here you:

Used the app's Context to get a reference to NotificationManagerCompat.
Called notify() on the NotificationManager passing in an identifier and the notification.

Re-run the application, delete the data from the menu Delete Data and reload it from the menu Load sample data item. If everything was successful, you should now see a notification icon in the status bar! Pull down the notification shade and you will see the full notification issued from your application indicating your sample data has loaded. Great!

Taking it a step further with Alarms

Issuing a notification after an action is performed is cool, but you are building a reminder application to administer medicine to your pets based on a schedule. This requires you to issue the notifications at some point in the future. The AlarmManager system service allows you to do just that. Notice, each item in the list of reminders includes the days and time to administer the medicine. You will use this information to schedule the alarms in the next section.

Creating an Alarm to send a Notification

In order to create an alarm to trigger a notification, you will need to do the following:

Create notification channels for each pet type.
Determine the time and date to schedule the alarm.
Create a PendingIntent to add to the alarm.
Schedule it with the AlarmManager.
Register a BroadcastReceiver to listen for the alarm.
Create the notification and issue it.

1. Pet Type Notification Channel's

Since you already have experience creating notification channels, just copy this code and paste it into the onCreate() method of the application class PetRx.kt.

// 1 NotificationHelper.createNotificationChannel(this,     NotificationManagerCompat.IMPORTANCE_LOW, true,     ReminderData.PetType.Cat.name, "Notification channel for cats.") // 2 NotificationHelper.createNotificationChannel(this,     NotificationManagerCompat.IMPORTANCE_HIGH, true,     ReminderData.PetType.Dog.name, "Notification channel for dogs.") // 3 NotificationHelper.createNotificationChannel(this,     NotificationManagerCompat.IMPORTANCE_NONE, false,     ReminderData.PetType.Other.name, "Notification channel for other pets.")

Notice that, for each channel, you specify a different level of importance. When creating channels, you should carefully think about the user experience you are creating.

Channels & Importance

Cats: NotificationManagerCompat.IMPORTANCE_LOW – Low notification importance: shows everywhere, but is not intrusive.
Dogs: NotificationManagerCompat.IMPORTANCE_HIGH – Higher notification importance: shows everywhere, allowed to makes noise and peek.
Other: NotificationManagerCompat.IMPORTANCE_NONE – A notification with no importance: shows nowhere, is blocked.

Because the application supports multiple pet types, and you want to stay organized, it's important to add a channel for each different pet type. This will allow your users to configure specific behavior based on that pet's type and control them individually from the device's app settings.

Open the overflow menu and tap Manage Channels to see the registered channels for your application.

2. Alarm Time

The sample app contains a model named ReminderData. Each ReminderData object contains both a time and a list of days. When the user creates the reminder, this information is input and saved to a local database. You'll make use of the ReminderData when working with the AlarmManager to create an alarm. More on this in a bit.

3. Creating the PendingIntent

Open the AlarmScheduler.kt file under the notif package and navigate to the createPendingIntent(): PendingIntent? method.

Add the following code:

// 1 val intent = Intent(context.applicationContext, AlarmReceiver::class.java).apply {   // 2   action = context.getString(R.string.action_notify_administer_medication)   // 3   type = "$day-${reminderData.name}-${reminderData.medicine}-${reminderData.type.name}"   // 4   putExtra(ReminderDialog.KEY_ID, reminderData.id) } // 5 return PendingIntent.getBroadcast(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)

Here you:

Create the Intent with a destination of AlarmReceiver::class.java (this class should already exist, but you'll fill it in in the next section).
Set the action for the Intent.
Set the type – This has to be unique so you construct it using the day, the pet's name, the medicine and the pet type. If this is not unique it will overwrite any other PendingIntent with this same type. If you are interested you can read more about how two Intent's are considered equal.
Add the reminder's ID in the Intent's bundle so you can use it in the AlarmReceiver.
Create the PendingIntent using the getBroadcast() method. This is very important because you are creating the Intent with a BroadcastReceiver as a target.

4. Scheduling the Alarm

Now that the notification channels are set up and you have created a unique PendingIntent for each reminder, it's time to actually schedule the alarms.

Open the AlarmScheduler.kt file and find the scheduleAlarm() method.
Add the following code:

// 1 val datetimeToAlarm = Calendar.getInstance(Locale.getDefault()) datetimeToAlarm.timeInMillis = System.currentTimeMillis() datetimeToAlarm.set(HOUR_OF_DAY, reminderData.hour) datetimeToAlarm.set(MINUTE, reminderData.minute) datetimeToAlarm.set(SECOND, 0) datetimeToAlarm.set(MILLISECOND, 0) datetimeToAlarm.set(DAY_OF_WEEK, dayOfWeek) // 2 val today = Calendar.getInstance(Locale.getDefault()) if (shouldNotifyToday(dayOfWeek, today, datetimeToAlarm)) {   alarmMgr.setRepeating(AlarmManager.RTC_WAKEUP,       datetimeToAlarm.timeInMillis, (1000 * 60 * 60 * 24 * 7).toLong(), alarmIntent)   return } // 3 datetimeToAlarm.roll(WEEK_OF_YEAR, 1) alarmMgr.setRepeating(AlarmManager.RTC_WAKEUP,     datetimeToAlarm.timeInMillis, (1000 * 60 * 60 * 24 * 7).toLong(), alarmIntent)

You just did three important things:

Set up a Calendar for the alarm's time using the ReminderData.
Checked whether that alarm should be scheduled today and scheduled it if so.
Else, schedule the alarm to repeat every week at that time.

5. Create a BroadcastReceiver

There are just a few more things to consider when dealing with alarms, but how do they tie back into the notifications? Well, the instances of PendingIntent you registered through the AlarmManager were created using the PendingIntent.getBroadcast() method. This method allows you to send a broadcast to the system that notifies any listeners of the action you set for the Intent.

Open a file named AlarmReceiver in the notif package. Make sure it inherits from the BroadcastReceiver() base class and implement the onReceive() method.

if (context != null && intent != null && intent.action != null) {   // 1   if (intent.action!!.equals(context.getString(R.string.action_notify_administer_medication), ignoreCase = true)) {     if (intent.extras != null) {      // 2       val reminderData = DataUtils.getReminderById(intent.extras!!.getInt(ReminderDialog.KEY_ID))       if (reminderData != null) {         // 3         NotificationHelper.createNotificationForPet(context, reminderData)       }     }   } }

With this code, you:

Check that the Intent's action matches the one from the Intent you created above.
Looked up the ReminderData in the database using the extra from the Intent's Bundle.
Create the notification using the ReminderData.

Open AndroidManifest.xml and register the AlarmReceiver by adding this xml inside the application tag:

          <receiver android:name=".notif.AlarmReceiver" />

All right, you have finally made it to the last step! Now you will issue the notification for the pet's medication.

6. Create the Notification and Issue It

Open the NotificationHelper class one more time, navigate to the createNotificationForPet()method and add the following code:

// 1 val groupBuilder = buildGroupNotification(context, reminderData) // 2 val notificationBuilder = buildNotificationForPet(context, reminderData) // 3 val administerPendingIntent = createPendingIntentForAction(context, reminderData) notificationBuilder.addAction(   R.drawable.baseline_done_black_24,    context.getString(R.string.administer),    administerPendingIntent) // 4 val notificationManager = NotificationManagerCompat.from(context) notificationManager.notify(reminderData.type.ordinal, groupBuilder.build()) notificationManager.notify(reminderData.id, notificationBuilder.build())

Here you:

Create a group notification.
Create a notification for the pet.
Add an action to the notification for the pet.
Called notify using NotificationManager for both notifications.

1. Create a Group Notification

Group notifications, along with channels, help you stay organized as more notifications are introduced into your applications. They will help the notifications issued from your app group together in the notification shade. Since the sample app supports reminders for cats, dogs and other pets, you already have the groups you need to get started.

Modify the buildGroupNotification(context: Context, reminderData: ReminderData)method like below:

private fun buildGroupNotification(context: Context, reminderData: ReminderData): NotificationCompat.Builder {   // 1   val channelId = "${context.packageName}-${reminderData.type.name}"   return NotificationCompat.Builder(context, channelId).apply {     setSmallIcon(R.drawable.ic_stat_medicine)     setContentTitle(reminderData.type.name)     setContentText(context.getString(R.string.group_notification_for, reminderData.type.name))     setStyle(NotificationCompat.BigTextStyle()         .bigText(context.getString(R.string.group_notification_for, reminderData.type.name)))     setAutoCancel(true)     setGroupSummary(true) // 2     setGroup(reminderData.type.name) // 3   } }

Using the same channelId, create the group notification.
Set this notification as the group summary (useful on versions of Android prior to API 24).
Set the group to the pet type name (i.e. Cat, Dog, or Other).

2. Create a Notification

Next, you need to create the notification using the same channelId. This time, you will also add a large icon to the notification to make it distinguishable from the other pet types.

Navigate to the buildNotificationForPet(context: Context, reminderData: ReminderData) method and modify it like below:

private fun buildNotificationForPet(context: Context, reminderData: ReminderData): NotificationCompat.Builder {   // 1   val channelId = "${context.packageName}-${reminderData.type.name}"   return NotificationCompat.Builder(context, channelId).apply {     setSmallIcon(R.drawable.ic_stat_medicine)     setContentTitle(reminderData.name)     setAutoCancel(true)     // 2     val drawable = when (reminderData.type) {       ReminderData.PetType.Dog -> R.drawable.dog       ReminderData.PetType.Cat -> R.drawable.cat       else -> R.drawable.other     }     // 3     setLargeIcon(BitmapFactory.decodeResource(context.resources, drawable))     setContentText("${reminderData.medicine}, ${reminderData.desc}")     // 4     setGroup(reminderData.type.name)     if (reminderData.note != null) {       setStyle(NotificationCompat.BigTextStyle().bigText(reminderData.note))     }     val intent = Intent(context, MainActivity::class.java).apply {       flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK       putExtra(ReminderDialog.KEY_ID, reminderData.id)     }     val pendingIntent = PendingIntent.getActivity(context, 0, intent, 0)     setContentIntent(pendingIntent)   } }

Build the Notification using the same channelId as the group notification.
Using the ReminderData get a drawable reference for the large icon.
Apply the large icon to the notification.
Set the notification's group.

3. Add an Action to the Notification

Actions help provide quick access to features that aren't necessarily scoped to the in-app experience. Say, for example, you receive a notification from your email client and you either want to respond to it or archive the email. Actions can provide this behavior.

Navigate to createPendingIntentForAction() in NotificationHelper and add the following code:

// 1 val administerIntent = Intent(context, AppGlobalReceiver::class.java).apply {   action = context.getString(R.string.action_medicine_administered)   putExtra(AppGlobalReceiver.NOTIFICATION_ID, reminderData.id)   putExtra(ReminderDialog.KEY_ID, reminderData.id)   putExtra(ReminderDialog.KEY_ADMINISTERED, true) } // 2 return PendingIntent.getBroadcast(context, ADMINISTER_REQUEST_CODE, administerIntent, PendingIntent.FLAG_UPDATE_CURRENT)

Create an Intent to launch the AppGlobalReceiver
Wrap the Intent in a PendingIntent

Note: The AppGlobalReceiver has been created and registered in the AndroidManifest.xml for you.

Finally, build and re-run the application to see this all in action. When the app is running delete and reload the sample data and the alarms will schedule in the background. When the notifications display, you should see them group together and have an action to update the medicine as administered.

Note: The progression of notifications grouping, depicted over time.

Wow! Look at you go. Now you have a fully functional application for reminding you to administer medication to your pets.

Where to Go From Here?

If you had trouble completing the tutorial, the final project is available in the original download under the PetMedicineReminder-Finished folder. Download it using the Download Materials button found at the top or bottom of this tutorial. For some additional features in the application, please poke around the source code.

In this tutorial, you have learned how to create notifications, notification channels, notification groups, and customize their display and behavior. You have learned how to add actions to notifications and work with the AlarmManager to schedule notifications to display in the future. You have also taken a brief look into the BroadcastReceiver.

If you have any questions or comments, please feel free to join the discussion below or reach out for more details. Good luck and happy coding!

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