---
title: "NestedScrollDispatcher"
description: "Nested scroll events dispatcher to notify the nested scroll system about the scrolling events
that are happening on the element.

If the element/modifier itself is able to receive scroll events (from the touch, fling, mouse,
etc) and it would like to respect nested scrolling by notifying elements above, it should
properly dispatch nested scroll events when being scrolled

It is important to dispatch these events at the right time, provide valid information to the
parents and react to the feedback received from them in order to provide good user experience
with other nested scrolling nodes."
type: "class"
---

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


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

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


```kotlin
class NestedScrollDispatcher
```


Nested scroll events dispatcher to notify the nested scroll system about the scrolling events
that are happening on the element.

If the element/modifier itself is able to receive scroll events (from the touch, fling, mouse,
etc) and it would like to respect nested scrolling by notifying elements above, it should
properly dispatch nested scroll events when being scrolled

It is important to dispatch these events at the right time, provide valid information to the
parents and react to the feedback received from them in order to provide good user experience
with other nested scrolling nodes.


## Properties

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


```kotlin
val coroutineScope: CoroutineScope
```


Get the outer coroutine scope to dispatch nested fling on.

There might be situations when then component that is dispatching preFling or postFling to
parent can be disposed together with its scope, so it's recommended to use launch nested
fling dispatch using this scope to prevent abrupt scrolling user experience.

**Note:** this scope is retrieved from the parent nestedScroll participants, unless the node
knows its parent (which is usually after first composition commits), this will throw
`IllegalStateException`.



## Functions

```kotlin
fun dispatchPreScroll(available: Offset, source: NestedScrollSource): Offset
```


Dispatch pre scroll pass. This triggers `NestedScrollConnection.onPreScroll` on all the
ancestors giving them possibility to pre-consume delta if they desire so.

#### Parameters

| | |
| --- | --- |
| available | the delta arrived from a scroll event |
| source | the source of the scroll event |


#### Returns

| | |
| --- | --- |
|  | total delta that is pre-consumed by all ancestors in the chain. This delta is unavailable for this node to consume, so it should adjust the consumption accordingly |



```kotlin
fun dispatchPostScroll(
        consumed: Offset,
        available: Offset,
        source: NestedScrollSource,
    ): Offset
```


Dispatch nested post-scrolling pass. This triggers `NestedScrollConnection.onPostScroll` on
all the ancestors giving them possibility to react of the scroll deltas that are left after
the dispatching node itself and other `NestedScrollConnection`s below consumed the desired
amount.

#### Parameters

| | |
| --- | --- |
| consumed | the amount that this node consumed already |
| available | the amount of delta left for ancestors |
| source | source of the scroll |


#### Returns

| | |
| --- | --- |
|  | the amount of scroll that was consumed by all ancestors |



```kotlin
suspend fun dispatchPreFling(available: Velocity): Velocity
```


Dispatch pre fling pass and suspend until all the interested participants performed velocity
pre consumption. This triggers `NestedScrollConnection.onPreFling` on all the ancestors
giving them a possibility to react on the fling that is about to happen and consume part of
the velocity.

#### Parameters

| | |
| --- | --- |
| available | velocity from the scroll evens that this node is about to fling with |


#### Returns

| | |
| --- | --- |
|  | total velocity that is pre-consumed by all ancestors in the chain. This velocity is unavailable for this node to consume, so it should adjust the consumption accordingly |



```kotlin
suspend fun dispatchPostFling(consumed: Velocity, available: Velocity): Velocity
```


Dispatch post fling pass and suspend until all the interested participants performed velocity
process. This triggers `NestedScrollConnection.onPostFling` on all the ancestors, giving them
possibility to react of the velocity that is left after the dispatching node itself flung
with the desired amount.

#### Parameters

| | |
| --- | --- |
| consumed | velocity already consumed by this node |
| available | velocity that is left for ancestors to consume |


#### Returns

| | |
| --- | --- |
|  | velocity that has been consumed by all the ancestors |