EggTimer - Final Code

Solution code for Advanced Android with Kotlin Codelab

Content: http://codelabs.developers.google.com/codelabs/advanced-android-kotlin-training-notifications

Introduction

EggTimer is a timer app for cooking eggs. You can start and stop the timer, choose different cooking intervals.

In this codelab, working from this starter app, you:

• Add notitications to the eggtimer app.
• Use channels and importance for the app notifications.
• Customize and style the notifications.

Pre-requisites

You should be familiar with:

• Services, AlarmManager, Broadcast Receivers.

Lab path

3. Getting started

1. AlarmReceiver.kt

   AlarmReceiver is triggered by the AlarmManager to send the notification when the user-defined timer is up.

2. SnoozeReceiver.kt

   SnoozeReceiver handles the user click to snooze the notification.

3. EggTimerFragment.kt

   EggTimerFragment is part of the UI portion of the app.

4. EggTimerViewModel.kt

   EggTimerViewModel is responsible for starting and canceling the timer and for other lifecycle-related app tasks.

5. BindingUtils.kt

   Binding adapters to enable data binding between the app UI and the ViewModel.

6. NotificationUtils.kt

   Extension methods on the NotificationManager.

4. Add Notifications to your app

Using notifications is a great way to get the attention of your users to your app. Whether your app is not running or running in the foreground, a notification will show a popup window on top of the screen and may include sound or vibration. To create a notification, you need to use a notification builder and provide a title text, a content text, and an icon. Once the builder has all the necessary fields, NotificationManager, which is a system service, helps you to display this content as a notification. NotificationManager is responsible for sending a notification, updating its contents, and canceling the notification.

4.1. Create a basic Notification

1. NotificationUtils.kt
   • Step 1.1 - Extension function to send messages
   • Step 1.2 - Get an instance of NotificationCompat.Builder
   • Step 1.3 - Set title, text and icon to builder
   • Step 1.4 - Call notify
2. EggTimerViewModel.kt
   • Step 1.5 - Get an instance of NotificationManager and call sendNotification

4.2. Notification Channels

Starting with API level 26, all notifications must be assigned to a channel. If you tap and hold the app launcher icon, select app info, and tap notifications, you will see a list of notification channels associated with the app. Right now the list is empty because your app has not created any channels.

Channels represent a type of notification — for example, your egg timer can send a notification when the egg is cooked, and also use another channel to send daily notifications to remind you to have eggs with your breakfast. All notifications in a channel are grouped together, and users can configure notification settings for a whole channel. This allows users to personalize their notification settings based on the kind of notification they are interested in. For example, your users can disable the breakfast notifications, but still choose to see the notifications from the timer.

Developers set the initial settings, importance and behavior, to be applied to all notifications in a channel. After you set the initial settings, users can override these settings.

1. EggTimerViewModel.kt
   • Step 1.6 - Create a channel
   • Step 1.7 - Call create channel

4.3. Add notifications to your app

1. AlarmReceiver.kt
   • Step 1.9 - Add call to sendNotification
   • Step 1.10 - Remove toast
2. EggTimerViewModel.kt
   • Step 1.10 - Remove the notification code

4.4. Add a content intent

Showing the notification and informing the user is great, but when a user clicks a notification, they expect to go back to the corresponding app.

An Intent is a messaging object you can use to request an action from another app component. Intents can be used for starting an activity, a service, or delivering a broadcast. In this case, you use this intent to tell the system to open MainActivity when the user taps the notification. Since your app consists of only a single view, you do not have many options here. However, in a larger app, the notification should create a seamless experience by bringing the user to a screen which makes sense for when they interact with the notification.

1. NotificationUtils.kt
   • Step 1.11 - Create Intent
   • Step 1.12 - Create PendingIntent
   • Step 1.13 - Set content intent

4.5. Cancel the notification

You have a functional egg timer with notifications, but there is a small issue. If you set the timer, get a notification, and set the timer again, the previous notification stays on the status bar while the new timer is running. This can confuse your user if the app is in the background, and may result in undercooked eggs.

To fix this, you need to clear the previous notification when you start a new timer.

1. NotificationUtils.kt
   • Step 1.14 - Cancel all notifications
2. EggTimerViewModel.kt
   • Step 1.15 - Call cancel notification

5. Customizing Notifications

5.1. Style your notification

Styling your notification according to your needs and the notification content will make your notifications stand out and look more like an extension of your application. The notification framework comes with several built-in styles to help, and you can always create your own.

NotificationCompat offers built-in styles for:

• BigTextStyle, which can display a large block of text, such as showing the contents of an email when expanded.
• BigPictureStyle, which shows large-format notifications that include a large image attachment.
• InboxStyle, which shows a conversation style text content.
• MediaStyle, which shows controls for media playback.
• MessagingStyle, which shows large-format notifications that include multiple messages between any number of people.

1. NotificationUtils.kt
   • Step 2.0 - Add style
   • Step 2.1 - Add style to builder

5.2. Notification actions

Notification actions are another customization you can add to your notifications. Your notifications currently redirect to your app when users click on them. In addition to this default notification action, you can add action buttons that complete an app-related task from the notification.

A notification can offer up to three action buttons that allow the user to respond quickly, such as snooze a reminder or reply to a text message. These action buttons should not duplicate the action performed when the user taps the notification.

To add an action button, pass a PendingIntent to the addAction() function on the builder. This is similar to setting up the notification's default tap action by calling setContentIntent(), except instead of launching an activity, you can do a variety of other things, for example, start a BroadcastReceiver that performs a job in the background so the action does not interrupt the app that's already open.

1. SnoozeReceiver.kt
   • Step 2.2 - Cancel all notifications
2. NotificationUtils.kt
   • Step 2.2 - Add snooze action
   • Step 2.3 - Add snooze action

5.3. Notification importance

Importance determines how much the notification should interrupt the user visually and audibly. Notifications with higher importance will be more interruptive to users.

You must specify the importance level in the NotificationChannel constructor. The importance level you assign to a channel applies to all notification messages that you post to it.

Importance (Android 8.0 and higher)	Priority (Android 7.1 and lower)	User-visible importance level
IMPORTANCE_HIGH	PRIORITY_HIGH/PRIORITY_MAX	Makes a sound and appears as a heads-up notification (pops up at the top of the screen)
IMPORTANCE_DEFAULT	PRIORITY_DEFAULT	Make a sound
IMPORTANCE_LOW	PRIORITY_LOW	No sound
IMPORTANCE_MIN	PRIORITY_MIN	No sound and does not appear in the status bar

1. EggTimerFragment.kt
   • Step 2.4 - Change importance
2. NotificationUtils.kt
   • Step 2.5 - Set priority

5.4. Notification badges

Notification badges are small dots that appear on the launcher icon of the associated app when the app has an active notification. Users can long-press on the app icon to reveal the notifications.

These dots, called badges, appear by default, and there's nothing your app needs to do. However, there might be situations where badges don't make sense for your notifications, so you can disable them on a per-channel basis.

1. EggTimerFragment.kt
   • Step 2.6 - Disable badges for this channel

References

• Intents and Intent Filters
• Notification design guide