How to migrate PHPhotoLibraryChangeObserver to Swift 6?

Question

tovkal OP

Created Jun ’24

Replies 2

Boosts 0

Participants 2

I have the following code:

extension AssetGridViewController: PHPhotoLibraryChangeObserver {
    func photoLibraryDidChange(_ changeInstance: PHChange) {
        Task { @MainActor in
            guard let changes = changeInstance.changeDetails(for: fetchResult) else { return }
            fetchResult = changes.fetchResultAfterChanges
        }
    }
}

With Swift 6, this generates a compilation error: Main actor-isolated instance method 'photoLibraryDidChange' cannot be used to satisfy nonisolated protocol requirement. The error includes to fix-it suggestions:

Adding nonisolated to the function (nonisolated func photoLibraryDidChange(_ changeInstance: PHChange))
Adding @preconcurrency to the protocol conformance (extension AssetGridViewController: @preconcurrency PHPhotoLibraryChangeObserver {)

Both options generate a runtime error: EXC_BREAKPOINT (code=1, subcode=0x105b7c400). For context, AssetGridViewController is a regular UIViewController.

Any ideas on how to fix this?

Boost

Answer 1

tovkal OP

Jun ’24

Here is a sample project with the issue, in case somebody wants to try it: https://github.com/tovkal/PhotoSwift6

0

Answer 2

DTS Engineer OP

Apple

Jul ’24

Three things:

The doc comments for PHPhotoLibraryChangeObserver make it clear that it’s not called on the main queue.
AssetGridViewController is a UIViewController.
UIViewController is isolated to the main actor by default.

Given all of the above, this method must be declared as non-isolated:

extension AssetGridViewController: PHPhotoLibraryChangeObserver {
    nonisolated func photoLibraryDidChange(_ changeInstance: PHChange) {
        // your code here
    }
}

You wrote:

Both options generate a runtime error

That’s surprising. If you write the code as its shown above, with the method being empty, do you still see it trap?

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