[Office Hours] SpeziScheduler - scheduling and deleting notifications

[kkellybonilla]

Related Discussion

Hi CS 342 Staff!

@PSchmiedmayer , I'd like to ask a question related to the SpeziScheduler notifications and the way it works.

Currently, I schedule a weekly notification in our scheduler's configure method at 9 AM every Saturday and Sunday, reminding the user to log their weight in the app.

If the user logs their weight on Saturday before the 9 AM notification, or after the 9 AM notification and before the Sunday 9 AM notification, I delete the remaining notifications for the current weekend. I do this by querying for these notifications by their ids with the queryTasks method and deleting them with the deleteTasks method.

When I delete the remaining notifications for the current weekend, will the scheduler still automatically schedule notifications for the following weekends as originally configured? Or does deleting a scheduled task remove it entirely, requiring me to re-schedule it post-deletion to ensure future notifications are still created?

Thanks!

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[PSchmiedmayer]

@lukaskollmer @Supereg Would you be able to answer this question?

[lukaskollmer]

@kkellybonilla based on your description, there's 2 issues here i think.

Let's, for now, ignore the fact that you have two tasks, and assume that only the saturday-one exists.

Firstly: when you call deleteTasks, you're not deleting the upcoming notifications, but instead you delete the whole Task from the scheduler (which makes it appear as though you deleted the notifications, since deleting a Task will of course also delete all of its upcoming notifications).

To give a broad overview of the module (sorry in advance if you already know this and i'm just explaining to you things you're already familiar with; IMO the explanation might still be useful for someone else in the future).

SpeziScheduler consists of the following key components:

1. Tasks, which are usually recurring actions you want the user (or your app) to perform
   • The Scheduler module's database stores all Tasks you define via the createOrUpdateTask function.
2. Events, which are individual occurrences of a Task.
   • Eg: if your app has a single, daily Task, the scheduler would contain that one Task, but an infinite amount of Events (for every day, there would be one event, for that task).
   • If you make the task weekly instead of daily, you'd still have an infinite amount of Events, with the difference that it'd be one per week rather than one per day.
   • Due to the possibly-infinite nature of events, they're not actually stored in a database, but rather simply computed on-demand, for a specific time range, based on the Tasks that are active in that time range and their respective schedules.
3. Outcomes, which model completed Events.
   • When you mark an event as completed, the Scheduler creates an Outcome object and stores it in its database.
   • This is also how the scheduler keeps track of which events have already been completed and which are still open: if the database contains a matching Outcome for some Event, we can consider it as being completed.

Tasks can optionally schedule notifications. In this case, even though you enable the notifications on a per-task level, they are actually scheduled on a per-event level: if you have a daily task, you have that single task in the scheduler, which then results in multiple events (one per day), and the scheduler will create one notification per event.

This is where you're going wrong, i think: deleting a task will delete all of its events, which in turn will of course also cancel all of the associated notifications.
But in the situation that the user logs their weight on saturday at eg 8AM (ie, prior to the notification) what you actually want, i think, would be to fetch the upcoming Event scheduled for the Task (ie, the 9AM event) and proactively mark the event as completed. This will also cancel the associated push notification. You can do this via the Event/complete(ignoreCompletionPolicy:with:) function. (Depending on the completion policy you specify in your task, you might need to pass true for the parameter here; otherwise you can ignore it.)

The second issue, and this isn't your fault but IMO rather a deficiency in the current version of SpeziScheduler, is that currently, every Event can have at most a single notification. Your intended use case of having two notifications per event simply cannot be expressed using the current Scheduler APIs.
You can work around this, as you already seen to be doing, by having two events (one for saturday and one for sunday). That would give you separate notifications on two days, but you'd probably also need to have internal special handling that takes this into account: eg, if the user logs their weight on saturday (thereby completing the saturday event in the first task), you'd need to programmatically complete the sunday event of the second task, in order to keep this in sync. Same thing the other way around: if the user logs their weight on sunday, you might want to retroactively also mark the saturday event as completed.

IMO, there should be an API that lets you specify that you want multiple notifications per event, but we currently don't have that.

[lukaskollmer]

@kkellybonilla sorry for missing this. i can have a look at this in a couple of days. can you maybe give me a link to a specific commit in your app repo, where this bug occurs?

[kkellybonilla]

no worries @lukaskollmer! it seems to be crashing everywhere i'm passing in a Schedule object to the SpeziScheduler methods. here's one of the lines where this error is being thrown: https://github.com/CS342/2025-Stanford-360/blob/04c2983e58f1acd1f9acfbfedd7a4d5592f61f45/Stanford360/Activity/Model/ActivityScheduler.swift#L81

[PSchmiedmayer]

@lukaskollmer Do you have an idea where this might originate from?

[lukaskollmer]

@PSchmiedmayer i've seen the same crash in the past; it seems to be related to storing the .once schedule in SwiftData. i created StanfordSpezi/SpeziScheduler#64 to track this

[kkellybonilla]

@lukaskollmer thanks for looking into this! do you have any recommendations for how I can achieve my desired functionality of sending a notification once and work around this for the time being?