Skip to content

darrarski/tca-ifletstore-effect-cancellation-demo

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

8 Commits
 
 
 
 
 
 
 
 
 
 

Repository files navigation

TCA: IfLetStore, Effect cancellation demo

Demo project. Reproduces the issue with IfLetStore and effect cancellation when using The Composable Architecture.

Issue

Steps to reproduce

  1. Clone the repository
  2. Open Demo.xcodeproj in Xcode 11.5
  3. Run the app in iPhone Simulator using Demo build scheme
  4. Tap "Present Detail"
  5. Observe timer on the screen
  6. Tap "Dismiss Detail"

Expected behavior

  1. Detail view disappears
  2. Timer effect is canceled

Actual behavior

  1. App crashes due to error:
Fatal error: "DetailAction.stopTimer" was received by an optional reducer when its state was "nil". This can happen for a few reasons:

* The optional reducer was combined with or run from another reducer that set "DetailState" to "nil" before the optional reducer ran. Combine or run optional reducers before reducers that can set their state to "nil". This ensures that optional reducers can handle their actions while their state is still non-"nil".

* An active effect emitted this action while state was "nil". Make sure that effects for this optional reducer are canceled when optional state is set to "nil".

* This action was sent to the store while state was "nil". Make sure that actions for this reducer can only be sent to a view store when state is non-"nil". In SwiftUI applications, use "IfLetStore".

Details

I assume the issue is caused by the fact, that DetailAction.stopTimer action is sent to a store using .onDisappear modifier on a SwiftUI view that is already removed from the hierarchy by the IfLetStore view.

I don't think it's a bug in The Composable Architecture, I think it's rather misuse of it. I am not sure if expected behavior can be achieved in the current implementation of the library.

The problem seems to be common, as it will be present whenever we send actions using .onDisappear view modifier, when the view is embedded in IfLetStore view. This concrete use case is probably a common one when implementing long-time-running effects that needs to be eventually canceled (when view disappears).

Solutions

Lifecycle Reducer - Solution proposed by Brandon Williams on Swift Forums is available on solution-lifecycle branch. There is also an open pull request.

Links

License

Copyright © 2020 Dariusz Rybicki Darrarski

License: GNU GPLv3

About

No description, website, or topics provided.

Resources

License

Stars

Watchers

Forks

Releases

No releases published

Packages

No packages published