UIKit `observe` Closure Stops Being Called

[juliensagot]

Description

Hi everyone, I’m experiencing a major issue with the observe closure when used in conjunction with sharing-grdb.

For some reason, the observe closure randomly stops being called whenever my SharedReader (backed by a FetchKeyRequest) value changes. This leads to crashes in my app, as I’m relying on that closure to generate snapshots for my collection view.

I’ve created a sample project here, where the issue is reproducible. It also includes a failing unit test (running it 5 times is usually enough to observe the issue).

issue.mov

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

No response

SwiftUI Navigation version information

No response

Destination operating system

iOS 18

Xcode version information

16.4.0

Swift Compiler version information

[mbrandonw]

Hi @juliensagot, this is a very difficult one for us to reproduce. In a span of discussing this issue for 20+ minutes I only reproduced it twice and Stephen once. We have some theories, but since it seems to be easier for you to reproduce, can you collect more info for us?

First, can you try removing the task?.cancel() from your code and see if you can reproduce in the simulator? It of course will not be 100% correct to remove cancellation because the order of the Task's may be wrong, but if it seems to fix the observation then that gives us more to work off of.

[juliensagot]

Hi @mbrandonw, sorry, I should have mentioned that it’s really hard to reproduce this on the simulator or preview. It’s much easier on a physical device (I’m testing on an iPhone 15 Pro), though still a bit tricky. Sometimes you need to spam the button for a while, but other times it happens almost instantly.

I’m still able to reproduce the issue even after removing the task?.cancel() line.