SwiftUI StateObject crash: “failed to demangle witness for associated type 'Property’”

Question

Created Jan ’23

Replies 4

Boosts 2

Views 1.6k

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Hello, we have weird crash in our app that mostly seems to happen right after launch. It is quite rare and so far I haven’t been able to reproduce it (the info below comes from Crashlytics).

The main error message I have is this:

failed to demangle witness for associated type 'Property' in conformance 'SwiftUI.StateObject<AppBlock.QuickBlockActivityViewModel>.(unknown context at $18f34e5b8).Box: DynamicPropertyBox' from mangled name '���yxG' - subject type x does not conform to protocol ObservableObject

And here is the stack trace:

Crashed: com.apple.main-thread
0  libsystem_kernel.dylib         0x7200 __pthread_kill + 8
1  libsystem_pthread.dylib        0x71ac pthread_kill + 268
2  libsystem_c.dylib              0x20ca0 abort + 180
3  libswiftCore.dylib             0x3d7304 swift::fatalError(unsigned int, char const*, ...) + 134
4  libswiftCore.dylib             0x3d7324 swift::warningv(unsigned int, char const*, char*) + 30
5  libswiftCore.dylib             0x3ee678 swift_getAssociatedConformanceWitnessSlowImpl(swift::TargetWitnessTable<swift::InProcess>*, swift::TargetMetadata<swift::InProcess> const*, swift::TargetMetadata<swift::InProcess> const*, swift::TargetProtocolRequirement<swift::InProcess> const*, swift::TargetProtocolRequirement<swift::InProcess> const*) + 2078
6  libswiftCore.dylib             0x3ecb9c swift_getAssociatedTypeWitness + 236
7  SwiftUI                        0x5b838 OUTLINED_FUNCTION_49 + 640
8  SwiftUI                        0xa8d68 OUTLINED_FUNCTION_513 + 16260
9  SwiftUI                        0x58244 OUTLINED_FUNCTION_177 + 10892
10 SwiftUI                        0x95524 OUTLINED_FUNCTION_1160 + 6632

We are using the view model (QuickBlockActivityViewModel) in a SwiftUI view that is part of collection view using the new UIHostingConfiguration from iOS 16.

Our view model is a subclass of view model for older iOS versions that conforms to ObservableObject and is marked as @MainActor.

And the view model is used like this: @StateObject private var viewModel = QuickBlockActivityViewModel()

Internally the view model uses Combine to monitor a couple of states from other parts of the app to modify its properties.

Answered by nemecek_f in 741919022

I tried not having the view model be a subclass which was itself conforming to ObservableObject and so far haven't seen a single crash report from this version.

It required to have some code duplication but seems like it might have worked

Boost

Answer 1

Claude31 OP

Jan ’23

Could this help ?

https://github.com/ra1028/DifferenceKit/issues/79

or turn off "dead code snipping" as suggested here:

https://developer.apple.com/forums/thread/126373 (referenced in https://stackoverflow.com/questions/59725439/failed-to-demangle-witness-error-when-using-realm-in-a-custom-publisher)

0

Answer 2

nemecek_f OP

Jan ’23

Thanks!

The crash we are seeing isn't related to any external dependency which both the solution posted seem to solve.

I am tempted to try changing the "Dead Code Stripping" but I am afraid of other repercusions this could have.

0

Answer 3

nemecek_f OP

Jan ’23

Accepted Answer

I tried not having the view model be a subclass which was itself conforming to ObservableObject and so far haven't seen a single crash report from this version.

It required to have some code duplication but seems like it might have worked

1

Answer 4

junyan72 OP

Feb ’24

I have experienced the same issue. My code was like:

In side the view:

@StateObject var foo: AbstractFoo

class AbstractFoo: ObservableObject {}
class Foo: AbstractFoo{}

I tried not having the view model be a subclass which was itself conforming to ObservableObject and so far haven't seen a single crash report from this version.

If the above is true, does that mean I'm not supposed to use inheritance for StateObject? Can someone from Apple please confirm?

1