Unexplained crash: NSInvalidArgumentException, same view controller instance pushed more than once - ios

Question

I'm seeing an unexplained crash on my iOS app built with SwiftUI. It only affects some users, and I can't manage to reproduce locally.
Here is the stack trace:
Fatal Exception: NSInvalidArgumentException
<_TtGC7SwiftUI41StyleContextSplitViewNavigationControllerVS_19SidebarStyleContext_: 0x110859800>
is pushing the same view controller instance(<_TtGC7SwiftUI41StyleContextSplitViewNavigationControllerVS_14NoStyleContext_: 0x11088a400>)
more than once which is not supported and is most likely an error in the application : `com.myapp`
Fatal Exception: NSInvalidArgumentException
0 CoreFoundation 0x1893a186c __exceptionPreprocess
1 libobjc.A.dylib 0x19e3bcc50 objc_exception_throw
2 UIKitCore 0x18b575514 -[UINavigationController pushViewController:transition:forceImmediate:]
3 UIKitCore 0x18b5751f4 -[UINavigationController pushViewController:animated:]
4 UIKitCore 0x18b6047c8 __45-[UISplitViewControllerPanelImpl showColumn:]_block_invoke
5 UIKitCore 0x18b57eda8 -[UINavigationController _executeSplitViewControllerActions:]
6 UIKitCore 0x18b6045bc -[UISplitViewControllerPanelImpl showColumn:]
7 UIKitCore 0x18b5e4c54 -[UISplitViewController showColumn:]
8 SwiftUI 0x1903784f4 closure #1 in closure #1 in NavigationBridge_PhoneTV.push(_:onto:animated:)
9 SwiftUI 0x19042728c thunk for #escaping #callee_guaranteed () -> ()
10 UIKitCore 0x18c23f544 -[_UIAfterCACommitBlock run]
11 UIKitCore 0x18bd6700c _runAfterCACommitDeferredBlocks
12 UIKitCore 0x18bd559a0 _cleanUpAfterCAFlushAndRunDeferredBlocks
13 UIKitCore 0x18bd89bb4 _afterCACommitHandler
14 CoreFoundation 0x18931c358 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__
15 CoreFoundation 0x1893165c4 __CFRunLoopDoObservers
16 CoreFoundation 0x189316b74 __CFRunLoopRun
17 CoreFoundation 0x18931621c CFRunLoopRunSpecific
18 GraphicsServices 0x1a0ee2784 GSEventRunModal
19 UIKitCore 0x18bd56ee8 -[UIApplication _run]
20 UIKitCore 0x18bd5c75c UIApplicationMain
21 MYAPP 0x100dbecc0 main + 7 (PushupsMode.swift:7)
22 libdyld.dylib 0x188fd66b0 start
Looking at PushupsMode.swift:7 it seems completely unrelated:
import Foundation
extension WorkoutModel {
mutating func startPushups() {
var pushupsCount = 10 + p.intensityOptionPicked * 10
if(round > 6 || round < 3) { // <<--- this is the line crashing
pushupsCount = Int(pushupsCount / 2)
}
// More code after that point
}
}
The round variable is defined in another file, but there's nothing really significant around it:
import Foundation
import SwiftUI
struct WorkoutModel: Identifiable {
// bunch of stuff before
var round: Int = -1
// bunch of stuff after
}
Obviously looking at the error message, it seems like something is getting pushed twice... however since I'm using SwiftUI I'm not entirely sure how I could have even done that.
Any pointers would be appreciated!

Answer 1

Your problem may be that you are defining pushupsCount as an Int( on PushupsMode.swift:8 which is causing the exception on :7 from :8 failing pre-execution. Try defining it as pushupsCount = Int pushupsCount / 2 .

Answer 2

Using pushViewController:transition:forceImmediate is not a good idea because pushViewController:animated will be calling on this undocumented method. Rather than changing transition this way you can use other documented methods for changing animation. This thread might be helpful for you. You will also need to add guard in pushViewController:animated and will also need to set transition.duration. Calling pushViewController again and again is perhaps causing crash of app.

Answer 3

This problem is caused when you place your navigationLink inside of a List with observed data.
How to fix :
Remove NavigationLink from inside of the list and place it outside.