---
title: Scroll Events
---
Package: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;com.codex.composer.api.v1.event <br/>
Canonical Name: com.codex.composer.api.v1.event.ServerScrollEvents & ClientScrollEvents

Composer provides two scroll event handlers to register to, [ClientScrollEvents](#clientscrollevents) and [ServerScrollEvents](#serverscrollevents). <br/>
Furthermore, both events have 3 priority layers, HIGH, MEDIUM and LOW, in order of execution.

## ClientScrollEvents:
Called when the scroll wheel is moved in any direction on the client. Event method is:
```java
/* Returns: true, if the processing for other scroll events & vanilla functionality should be cancelled. */
boolean onScroll(MinecraftClient client, @Nullable ClientWorld world, @Nullable ClientPlayerEntity player, double scrollAmount);
```
The interface also provides the following method:
```java
/* Sends a ScrollActionPayload to the server, triggering ServerScrollEvent on the passed channel. */
default void sync(Identifier channel, double scrollAmount);
```
This class also provides an abstract definition for the client scroll event, which lets you filter for a specific item in a specific hand:
```java
public static abstract class ItemFilterClientScrollEvent implements ClientScrollAction {
    private final hand, item {...}

    protected ItemFilterClientScrollEvent(Hand hand, Item item) {...}
    protected ItemFilterClientScrollEvent(Item item) {...}

    @Override // Original method
    public boolean onScroll(MinecraftClient client, @Nullable ClientWorld world, @Nullable ClientPlayerEntity player, double scrollAmount) {...}

    public abstract boolean onScroll(MinecraftClient client, ItemStack stack, @Nullable ClientWorld world, @Nullable ClientPlayerEntity player, double scrollAmount);
}
```
## ServerScrollEvents:
Called when a ClientScrollEvent sends a sync packet to the server.
```java
/* Same as ClientScrollEvent, but on the server side. The Identifier passed is the one the packet contained. */
boolean onScroll(Identifier channel, ServerPlayerEntity player, PacketSender sender, double scrollAmount);
```
The interface also provides the following method:
```java
/* Simple equals check, designed for "prettier" code. */
default boolean onChannel(Identifier channel, Identifier correctChannel);
```
## Example implementation:
**From Elixiry, for now unreleased mod made for Warfare SMP**
```java
@Environment(EnvType.CLIENT)
public class PotionGuideClientScrollEvent implements ClientScrollEvents.ItemFilterClientScrollEvent {
    public static final Identifier CHANNEL = Elixiry.identify("potion_guide_event"); // elixiry:potion_guide_event
    public static final PotionGuideScrollEvent INSTANCE = new PotionGuideScrollEvent();

    private PotionGuideScrollEvent() {...}

    @Override
    public boolean onScroll(MinecraftClient minecraftClient, ItemStack itemStack, @Nullable ClientWorld clientWorld, @Nullable ClientPlayerEntity clientPlayerEntity, double v) {
        if (clientPlayerEntity != null && clientPlayerEntity.shouldCancelInteraction()) { // shouldCancelInteraction = is shifting
            sync(CHANNEL, v);
            return true;
        }
        return false;
    }
}

public class PotionGuideServerScrollEvent interface ServerScrollEvents.ServerScrollAction {
    {...} // Channel, INSTANCE and constructor

    @Override
    public boolean onScroll(Identifier identifier, ServerPlayerEntity serverPlayerEntity, PacketSender packetSender, double v) {
        if (serverPlayerEntity.shouldCancelInteraction()) {
            ItemStack stack = serverPlayerEntity.getStackInHand(Hand.MAIN_HAND);
            PotionGuideItemData data = PotionGuideItemData.get(stack);
            boolean sign = Math.signum(v) == 1; // Is positive

            if (sign) data.flipNext();
            else data.flipPrevious();

            data.write(stack);
            return true;
        }
        return false;
    }
}