Enviroment Data lost in SwiftUI view

[apptekstudios]

Enviroment Data lost in SwiftUI view

[apptekstudios]

Thanks for reporting the issue @ryangittings. This is unexpected behaviour, the environment objects should be getting carried across to the cells...

I haven't been able to reproduce the crash with EnvironmentObject or managedObjectContext. Do you have any simple demo that reproduces the crash?

A few questions to help narrow it down:

• are you accessing the environment / environment object outside of the view body variable?
• Is there an exception logged to the console when crashing?

As a workaround until we find the cause, consider doing the following (passing the environment object directly to your cells):

struct ContentView: View {
	@EnvironmentObject var yourObject: ObjectType
	
	var body: some View {
		ASCollectionView {
			ASCollectionViewSection(...) { item in
				Text("Your cell contents")
					.environmentObject(self.yourObject)
			}
		}
	}
}

[ryangittings]

I found it was when using a tab view and switching between the tabs.

Nope it’s in the view body; I’ll see if I can reproduce the exception as soon as I can.

That was the workaround I’ve used, thanks for that!

[apptekstudios]

Closing this for now as it seems to be resolved in recent versions of SwiftUI. Please feel free to reopen if it recurs :)

[kerrmarin]

@apptekstudios I can reproduce the crash always by making these changes kerrmarin@cfb538d and then navigating the demo app to the "App Store Layout" demo then scrolling the top carousel

[apptekstudios]

@kerrmarin Thank you for the easy instructions to reproduce the error!

Unfortunately it seems that this is a SwiftUI bug, and I am unable to work around it within the library :(

I would recommend using the workaround I suggested above if utilising EnvironmentObject 👍

Further info from my debugging:

• Primary issue: SwiftUI is calling the view's body immediately on initialising a UIHostingController.
• This means there is no opportunity to add the UIHostingController to the view/VC hierarchy before there is attempted access to the environment object.

[kerrmarin]

Thanks for the feedback @apptekstudios. Do you think it's worth re-opening this issue until it's fixed? More for visibility than for anything else in case someone else comes looking for an answer :)

I'll also open a bug in the Swift bug tracker. If the issue is as you describe it should be pretty straightforward to create a demo project that shows the issue.

[apptekstudios]

Thanks for the feedback @apptekstudios. Do you think it's worth re-opening this issue until it's fixed? More for visibility than for anything else in case someone else comes looking for an answer :)

I've created a new issue #131 that outlines the bug and its workaround to make it easy for anyone having the problem :)