---
title: "RememberObserver"
description: "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][onRemembered] by the composition if it is [remember]ed 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][onForgotten] when it is no longer [remember]ed anywhere in that composition. If a
single instance is [remember]ed 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 [remember]ed 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"
type: "interface"
---

<div class='type'>Interface</div>


<a id='references'></a>

<div class='sourceset sourceset-common'>Common</div>



```kotlin
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 `remember`ed 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 `remember`ed anywhere in that composition. If a
single instance is `remember`ed 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 `remember`ed 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

```kotlin
public fun onRemembered()
```


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


```kotlin
public fun onForgotten()
```


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


```kotlin
public fun onAbandoned()
```


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