Lifecycle and retaining stores in memory #266

Hello @Nikola-Milovic and thanks for your questions!

1. Retained instances

As per documentation, InstanceKeeper retains things (not only Stores) over their scope recreation. This means that objects are not retained in memory forever, but only until its scope (e.g. a Decompose component, or a Fragment) is alive or is being recreated due to Android configuration changes. So it is very similar to AndroidX ViewModels.

As of Decompose, when you pop a component, its retained instances are destroyed (InstanceKeeper.Instance.onDestroy method is caled). If there is a stack of components and you rotate the screen, only the currently active component is recreated and its InstanceKeeper instances are retained. All components in the back stack are destroyed with all their retained instances. This matches the behaviour of AndroidX Fragments.

2. How does the Lifecycle fit in this story?

In general, the Lifecycle is just a way to be notified when the Lifecycle state changes. So you can subscribe to its state changes and do whatever logic you need. The Binder is just on of the use cases, it allows to subscribe/unsubscribe streams based on the Lifecycle (e.g. keep a View subscribed to a Store only while the Lifecycle is started, so the View does not re-render while the app is in background). You can use the Lifecycle on your own as well. E.g. you may create Reaktive's DisposableScope and dispose it in lifecycle.doOnDestroy {}. Or you may create a CoroutineScope and cancel it in the same way.

If you follow the Single Activity approach, then you probably have something like Fragments or Decompose components, for each "screen". Each Fragment/Component has its own Lifecycle, which allows you to individually track which screens are active and which are not. When a Fragment/Component is recreated due to Android configuration changes, its Lifecycle goes as follows: onStop -> onPause -> onDestroy -> [new instance created] -> onCreate -> onStart -> onResume. Any objects retained via InstanceKeeper are not destroyed and just transferred to the new Fragment/Component.