Why `rememberRetained` Resets On Screen Navigation

Hey there, fellow developers! Ever been scratching your head, wondering why your precious state, managed by rememberRetained, seems to vanish into thin air and reinitialize every time you navigate back to a screen? You're definitely not alone, and trust me, it's a common head-scratcher, especially when diving deep into frameworks like Circuit or even just complex Jetpack Compose navigation. We all expect rememberRetained to be our reliable friend, holding onto data even when our composables leave the composition for a bit, but sometimes, it throws us a curveball. Today, we're gonna unravel this mystery, specifically focusing on how Navigator injection into your Presenter can surprisingly lead to new Presenter instances and, consequently, that unexpected rememberRetained reinitialization. Understanding this behavior is absolutely crucial for building robust, state-persistent UIs that don't make your users (or you!) tear their hair out. So, let's dive in and demystify why your retained state isn't always, well, retained as you'd expect on screen navigation.

Understanding the rememberRetained Mystery

Alright, let's kick things off by really digging into what rememberRetained is all about and why it's so vital for sophisticated UIs, especially within a context like SlackHQ's Circuit library. At its core, rememberRetained is a super powerful Composable function designed to retain objects across configuration changes and even when a Composable leaves and re-enters the composition. Think of it like a magical pocket that holds onto your complex data, view models, or other stateful objects, preventing them from being re-created needlessly. When you rotate your phone, for instance, or when your app goes into the background and is later restored, rememberRetained should ensure that the same instance of your object is presented back to your UI. This is fundamentally different from remember, which only survives recompositions within the current composition scope, or rememberSaveable, which serializes and deserializes small, simple state. For larger, non-serializable objects or those with complex lifecycles, rememberRetained is often the go-to solution. Its promise is simple: I'll keep this object alive for as long as its host activity or fragment is alive, even if the UI itself is temporarily destroyed and rebuilt. However, as some of us have noticed, this promise seems to break down when navigating back to a screen, causing our rememberRetained values to reinitialize as if they were brand new. This observed behavior often leads to confusion because it contradicts the very purpose of rememberRetained. We set up our state, navigate away, and then return, only to find our counters reset, our lists reloaded, or our expensive objects re-instantiated. The initial assumption is usually that rememberRetained itself is failing, but as we'll soon discover, the real culprit often lies a bit deeper in how our application's architecture, particularly dependency injection and Presenter lifecycle, interacts with Compose's state retention mechanisms. It's a subtle but significant distinction that can make or break your app's performance and user experience. So, while rememberRetained is generally awesome and works as advertised, its interaction with specific architectural patterns, especially those involving Navigator and Presenter lifecycles, can introduce unexpected reinitialization scenarios. This is where understanding the system's underlying mechanics becomes paramount to debugging and ultimately fixing these tricky state issues. We need to look beyond the surface and consider the bigger picture of how our screens, presenters, and navigation stack truly operate.

The Plot Twist: Navigator Injection and Presenter Creation

Now, here's where the plot really thickens, guys. The core of this rememberRetained reinitialization mystery often boils down to a specific architectural pattern: injecting the Navigator directly into your Presenter. This might seem like a perfectly reasonable thing to do at first glance. After all, if your Presenter needs to trigger navigation actions, giving it access to the Navigator seems logical, right? But here's the catch: when you inject the Navigator into a Presenter, especially in a framework like Circuit where Presenters are typically managed by a Presenter.Factory, you might inadvertently be telling your system to create a brand new instance of that Presenter every single time the screen is displayed, including when you navigate back. Let me tell ya, this is a pretty common pitfall!

Think about it this way: your Presenter is responsible for business logic and state management for a particular screen. If your dependency injection (DI) setup or Circuit's internal Presenter resolution logic determines that a new Presenter instance is required because one of its dependencies (Navigator, in this case) is being provided in a way that doesn't align with state retention, then a new Presenter is precisely what you'll get. When a new Presenter is created, all its internal state, including anything declared with rememberRetained within that Presenter's scope, is naturally initialized anew. It's like buying a new house every time you return from a trip; you'd expect everything inside to be new, right? The previously retained objects associated with the old Presenter instance are simply gone because that instance itself is gone, replaced by a fresh one. This isn't rememberRetained failing; it's rememberRetained doing exactly what it's told, but within the context of a new parent object. This phenomenon is particularly relevant in component-based architectures where Presenters are tied to the lifecycle of the screen or route. If the screen's lifecycle causes the Presenter to be recreated (e.g., due to a new scope being created for the route), then rememberRetained inside that Presenter will follow suit. The Navigator itself might be an object that the DI container or Circuit sees as needing to be fresh for each screen instance or route, which then forces the recreation of anything that depends on it. This deep interaction between DI scope, Presenter lifecycle, and Composable state management is often overlooked, leading to these perplexing reinitialization bugs. It's a critical piece of the puzzle to understand why your retained state isn't behaving as expected when navigating back, transforming a simple state retention issue into a complex architectural one.

Is This Behavior Expected? A Deep Dive into Circuit

So, the burning question: is this rememberRetained reinitialization, triggered by Navigator injection and subsequent Presenter recreation, expected behavior in a system like Circuit? And the answer, my friends, is nuanced but generally, yes, under certain dependency injection (DI) configurations and architectural choices. It's not a bug in rememberRetained itself, nor is it inherently a flaw in Circuit. Instead, it's a consequence of how different components' lifecycles intersect and how dependencies are managed. Circuit, at its core, is an architecture library that helps you decouple your UI (views) from your business logic (presenters) and state. It provides a flexible way to associate Presenters with Screens (which represent routes). When you navigate to a Screen, Circuit uses a Presenter.Factory to create a Presenter instance for that screen. The crucial part here is when and how often that Presenter instance is created. If your dependency injection framework (be it Dagger, Koin, or even a custom factory pattern) is configured to provide a new Navigator instance every time a Presenter is requested for a screen that's being re-entered (e.g., popped off the back stack, then pushed again, or simply navigated back to), then any Presenter that depends on that Navigator will also be re-instantiated.

Circuit's Presenter lifecycle is typically tied to the Screen's lifecycle. When a screen is no longer active (e.g., navigated away from), its associated Presenter might be garbage collected or removed from the active scope, depending on how Navigator maintains its back stack and how Circuit integrates with it. When you navigate back to that screen, Circuit often sees it as a new