RememberObserver

Interface

Common
public interface RememberObserver

Objects implementing this interface are notified when they are initially used in a composition and when they are no longer being used.

An object is remembered by the composition if it is remembered in at least one place in a composition. Compose may implicitly remember an object if doing so is required to restart the composition later, such as for composable function parameters. An object is forgotten when it is no longer remembered anywhere in that composition. If a single instance is remembered in more than one location in the same composition, its onRemembered and onForgotten will be called for each location in the composition.

When objects implementing this interface is remembered and forgotten together, the order of onForgotten is guaranteed to be called in the opposite order of onRemembered. For example, if two objects, A and B are remembered together, A followed by B, onRemembered will be called first on A then on B. If they forgotten together then onForgotten will be called on B first then on A.

Implementations of RememberObserver should generally not expose those object references outside of their immediate usage sites. A RememberObserver reference that is propagated to multiple parts of a composition might remain present in the composition for longer than expected if it is remembered (explicitly or implicitly) elsewhere, and a RememberObserver that appears more once can have its callback methods called multiple times in no meaningful order and on multiple threads.

An object remembered in only one place in only one composition is guaranteed to,

  1. have either onRemembered or onAbandoned called
  2. if onRemembered is called, onForgotten will eventually be called

Functions

public fun onRemembered()

Called when this object is successfully remembered by a composition. This method is called on the composition's apply thread.

public fun onForgotten()

Called when this object is forgotten by a composition. This method is called on the composition's apply thread.

public fun onAbandoned()

Called when this object is returned by the callback to remember but is not successfully remembered by a composition.