从通知意图启动活动时重新创建 Android ViewModel

Question

I'm trying to create a timer app. When a user presses the timer, it will create a notification that the timer is running.

I'm using a view model to store my view data. What I would like is when the timer is started and the notification is created, when the user presses the notification, it launches the activity for the timer again and brings it to the top of the stack. The activity's view should retain the same view model data as before.

What's currently happening is that clicking on the notification creates a new activity in my back stack. This creates a new view model for this activity. When I press the back button, I can return to the old activity view.

I just need this old activity view to be brought back up to the stack, not to create a new activity.

My code in the view model to send a notification when the timer starts is this:

    private fun sendNotification() {

    val intent = Intent(context, MainActivity::class.java)

    val pendingIntent = PendingIntent.getActivity(context, 0, intent, 0)

    var builder = NotificationCompat.Builder(context, CHANNEL_ID)
        .setSmallIcon(R.drawable.ic_launcher_foreground)
        .setContentTitle("Pomodoro Timer")
        .setContentText("Pomodoro Timer is running")
        .setContentIntent(pendingIntent)
        .setPriority(NotificationCompat.PRIORITY_DEFAULT)

    with(NotificationManagerCompat.from(context)) {
        // notificationId is a unique int for each notification that you must define
        notify(1, builder.build())
    }
}

My view model from my activity onCreate is created like this:

    val dataBinding: ActivityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main)

    val timerFactory = TimerFactory(this)
    val timer = ViewModelProvider(this, timerFactory).get(Timer::class.java)

    dataBinding.timer = timer
    dataBinding.lifecycleOwner = this

How do I make my intent on the notification to retain and just bring the old activity and view model back to the top of the stack?

Answer 1

The pending intent in the notification is starting a new task, hence a new instance of MainActivity is created.

If you want to get back to the original MainActivity, declare MainActivity in Manifest as android:launchMode="singleTask" .

Also check the docs about Android launch modes.