---
title: "SnapshotInstanceObservers"
description: "The return result of [SnapshotObserver.onPreCreate] allowing the reads and writes performed in
the newly created snapshot to be observed"
type: "class"
---

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


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

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


```kotlin
@ExperimentalComposeRuntimeApi
public class SnapshotInstanceObservers(
    /**
     * Called whenever a state is read in the snapshot. This is called before the read observer
     * passed to [Snapshot.takeSnapshot] or [Snapshot.takeMutableSnapshot].
     *
     * This method is called in the same thread that reads snapshot state.
     */
    public val readObserver: ((Any) -> Unit)? = null,

    /**
     * Called just before a state object is written to the first time in the snapshot or a nested
     * mutable snapshot. This might be called several times for the same object if nested mutable
     * snapshots are created as the unmodified value may be needed by the nested snapshot so a new
     * copy is created. This is not called for each write, only when the write results in the object
     * be recorded as being modified requiring a copy to be made before the write completes. This is
     * called before the write has been applied to the instance.
     *
     * This is called before the write observer passed to [Snapshot.takeMutableSnapshot].
     *
     * This method is called in the same thread that writes to the snapshot state.
     */
    public val writeObserver: ((Any) -> Unit)? = null,
)
```


The return result of `SnapshotObserver.onPreCreate` allowing the reads and writes performed in
the newly created snapshot to be observed