Dismissing more than one feature

[nmalevich]

Description

When I have migrated to 1.9 version from 1.3 and started to use @ObservableState, @presents, observe {}(I use UIKit for UI) and all what you recommend. All is good and thank you for your effort to improve TCA.

But now I have one problem with dismiss dependency. I didn't have this problem when I used 1.3 version. The problem is when I execute dismiss() from dismiss dependency at my child feature, not only my child feature set nil, but the parent feature too. The parent feature is added to main reducer by Scope(state:action:) and child feature by .ifLet(state: .$destination, action: .destination)

Yes, I have tried to use just callback effects from child features, detect them in parent reducer and set destination nil and it works well. But I want to use more simple way and exactly want to understand why this bug reproduce

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

After dismiss() set nil for only one(child) feature

Actual behavior

After dismiss() set nil for two(parent and child) features

Steps to reproduce

I can't share all my project, because it's not mine and I don't have this opportunity, but I can share with you some logs and results

I will share with you two variants of my app. And this variants have only one difference

1. With bug. I have this sending line on View that is connected with child feature

2. No bug. I commented this sending line

This action "test" isn't detected on any reducers, so it can't influence for something

test1.txt

test2.txt

You can also pay your attention to logs like this "<decode: bad range for [%@] got [offs:346 len:932 within:0]>". I'm sure that this error log is connected with the problem

The Composable Architecture version information

1.9.0

Destination operating system

iOS 17.3

Xcode version information

15.2

Swift Compiler version information

swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: x86_64-apple-macosx14.0

[mbrandonw]

Hi @nmalevich, can you please provide a project that demonstrates the behavior you are seeing? I don't think this is an issue with the library so I am going to convert this to a discussion for now. We can re-open an issue if it turns out to be something wrong with TCA.

[nmalevich]

No, sorry, I can't provide my project. And yes, I can't say that this bug is only connected with TCA, I agree that can be my mistake. But for me it is really strange that one line which really wouldn't do anything, can influence somehow.

Maybe you can understand why sending effect that isn't detected wherever can be cause

[mbrandonw]

HI @nmalevich, if you attach _printChanges() to the root reducer you see see that as far as TCA is concerned dismiss is working just fine:

received action:
  HomeFeature.Action.actionSubjects(
    .destination(
      .presented(
        .subject(
          .destination(
            .presented(
              .scan(
                .actionNavigationBar(
                  .callback(.didTapLeftItemButton)
                )
              )
            )
          )
        )
      )
    )
  )
  (No state changes)

received action:
  HomeFeature.Action.actionSubjects(
    .destination(
      .presented(
        .subject(
          .destination(.dismiss)
        )
      )
    )
  )
  HomeFeature.State(
    _stateNavigationBar: NavigationBarFeature.State(…),
    _stateSubjects: HomeSubjectsFeature.State(
      _destination: .subject(
        SubjectFeature.State(
-         _destination: .scan(
-           ScanFeature.State(
-             stateNavigationBar: NavigationBarFeature.State(
-               backgroundColor: UICachedDeviceWhiteColor(),
-               leftItemImage: UIImage(),
-               leftItemPadding: 9.0,
-               title: "Scan",
-               titleColor: #1 UICachedDeviceWhiteColor()
-             )
-           )
-         ),
+         _destination: nil,
          _stateNavigationBar: NavigationBarFeature.State(…),
          _typedTask: ""
        )
      )
    )
  )

This shows that .didTapLeftItemButton is sent, which causes .dismiss to be sent, which then nils out the destination.

So any problem with navigation is due to SwiftUI not updating properly. There are lots of bugs in SwiftUI navigation, and it's what of the reasons why NavigationStack was introduced in iOS 16.

You can even put a print next to the NavigationLink to see that the view is re-computing and the state is correct:

.background {
  let _ = print("store.destination == nil", store.destination == nil)
  NavigationLink(…)
}

This will print:

store.destination == nil true
store.destination == nil false
store.destination == nil true

So, not much that can be done I'm afraid.

We have found that sometimes @Environment(\.dismiss) works around some SwiftUI bugs (though also can cause others). So if you use that in NavigationBarView instead of sending the didTapLeftItemButton button it looks like it works.

[nmalevich]

Hi @mbrandonw, thank you for detailed answer. It is really helpful
I have tried to replace Dependency(\.dismiss) with Environment(\.dismiss) and it just started working. So I'm grateful for your help

But I have faced with another problem. It pushes third view two times, after pop. I will send new project and you can look.
There is flow that you will need to do:
1->2->3->2->1->2->3(digits are screens)

I will be waiting your answer
DismissErrorExample.zip

[nmalevich]

@mbrandonw Hi
Could I ask you have tried to produce this bug or you are going to?
I look forward to your answer, thank you

[mbrandonw]

Hi @nmalevich, I'm sorry but this is still navigation bugs in SwiftUI. I don't know of any workaround, other than to use NavigationStack with a binding, which we call "stack-based navigation." You can read our docs about how to do that, as well as the pros and cons between stack-based and tree-based navigation here.

[nmalevich]

@mbrandonw Hi
Thank you for your answer. Ok, I suppose I will increase target to 16.0 and will use NavigationStack. I hope it will change the situation
Thanks a lot