Push Notifications pt.2

In Part 1 we learned how to send push notifications from Firebase Cloud Messaging console. There are a number of improvements we can make:

• Show notification when the app in in the foreground
• Go to a specific view in the app when clicked
• Buttons directly in the notifications
• Keep the notification open while the app is open

Let’s get started!

Show notification in foregrounded app

First of all, the documentation for Android notifications is great. Here are a few useful links:

• Notification overview
• Create a notification
• Notification anatomy

Creating a notification channel

From Android API level 26, all notifications need to be assigned to a notification channel. The reason for this is that the user can control notifications per channel for an app. In my app below you could disable notifications about Taxis, while keeping the one for E-mails.

This code will only be called for API level 26 and above.

class MainActivity : AppCompatActivity() {

    private fun createNotificationChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val importance = NotificationManager.IMPORTANCE_HIGH
            val channelID = "Some channel ID"
            val channelName = "E-mail"
            val channelDescription = "Information about e-mail"
            val channel = NotificationChannel(channelID, channelName, importance).apply {
                description = channelDescription
            }

            val notificationManager: NotificationManager =
                getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            notificationManager.createNotificationChannel(channel)
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        createNotificationChannel()

        // We will create the notification here next
        ...
    }
}

More info here: Android: notification channels.

Creating a notification

Now we can create a notification that is shown when the user opens the app

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        createNotificationChannel()

        sendNotification()
    }

    private fun sendNotification() {
        // Note: if Android API level is less than 26, the channelID will be ignored
        val notificationBuilder = NotificationCompat.Builder(this, channelID)
            .setContentTitle("Hello Notification! \uD83D\uDC7B")
            .setContentText("This is the notification text \uD83D\uDC4F")
            .setSmallIcon(R.drawable.ic_launcher_foreground)

        val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        notificationManager.notify(1, notificationBuilder.build())
    }

Now if we build the app:

(Optional) Add a button that will trigger the notification

activity_main.xml

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
                                                   xmlns:app="http://schemas.android.com/apk/res-auto"
                                                   xmlns:tools="http://schemas.android.com/tools"
                                                   android:layout_width="match_parent"
                                                   android:layout_height="match_parent"
                                                   tools:context=".MainActivity">

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello World!"
            app:layout_constraintBottom_toTopOf="@+id/notify_button"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>

    <!-- Added -->
    <Button
            android:id="@+id/notify_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="280dp"
            android:text="Notify!"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

ActivityMain.kt

    override fun onCreate(savedInstanceState: Bundle?) {
        ...
        notify_button.setOnClickListener {
            sendNotification()
        }
    }

Code

The code for the push notification is foreground mode is here.

Go to specific view

When the user clicks on a notification, the app will open with the main activity active. In many cases we want to go an activity that is related to the notification itself. For example, if we get a notification that our taxi has arrived, we could open a screen with that particular ride. We do this by passing an intent to the notification (more information here).

1. Create a new Activity (File > New > Activity > Empty Activity). For example, DetailsActivity
2. Create an Intent and add it to the notificationBuilder

    private fun sendNotification() {
        val intent = Intent(this, DetailsActivity::class.java).apply {
            flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
        }
        val pendingIntent: PendingIntent = PendingIntent.getActivity(this, 0, intent, 0)


        // Note: if Android API level is less than 26, the channelID will be ignored
        val notificationBuilder = NotificationCompat.Builder(this, channelID)
            ...
            .setContentIntent(pendingIntent)
            .setAutoCancel(true)

        val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        notificationManager.notify(1, notificationBuilder.build())
    }

Set setAutoCancel(true) will make sure that the notification disappears when the user clicks it. Here is the result.

Code

The code to go to a specific view is here.