Add LivingSwapHandItemsEvent

src/main/java/net/minecraftforge/common/ForgeHooks.java

@@ -160,6 +160,7 @@ import net.minecraftforge.event.entity.living.LivingChangeTargetEvent.ILivingTar
 import net.minecraftforge.event.entity.living.LivingFallEvent;
 import net.minecraftforge.event.entity.living.LivingHurtEvent;
 import net.minecraftforge.event.entity.living.LivingKnockBackEvent;
+import net.minecraftforge.event.entity.living.LivingSwapItemsEvent;
 import net.minecraftforge.event.entity.living.LivingUseTotemEvent;
 import net.minecraftforge.event.entity.living.LootingLevelEvent;
 import net.minecraftforge.event.entity.living.ShieldBlockEvent;
@@ -1226,6 +1227,13 @@ public class ForgeHooks
         return e;
     }
 
+    public static LivingSwapItemsEvent.Hands onLivingSwapHandItems(LivingEntity livingEntity)
+    {
+        LivingSwapItemsEvent.Hands event = new LivingSwapItemsEvent.Hands(livingEntity);
+        MinecraftForge.EVENT_BUS.post(event);
+        return event;
+    }
+
     public static void writeAdditionalLevelSaveData(WorldData worldData, CompoundTag levelTag)
     {
         CompoundTag fmlData = new CompoundTag();
@@ -1536,7 +1544,7 @@ public class ForgeHooks
      * Handles living entities being under water. This fires the {@link LivingBreatheEvent} and if the entity's air supply
      * is less than or equal to zero also the {@link LivingDrownEvent}. Additionally when the entity is under water it will
      * dismount if {@link IForgeEntity#canBeRiddenUnderFluidType(FluidType, Entity)} returns false.
-     * 
+     *
      * @param entity           The living entity which is currently updated
      * @param consumeAirAmount The amount of air to consume when the entity is unable to breathe
      * @param refillAirAmount  The amount of air to refill when the entity is able to breathe

src/main/java/net/minecraftforge/event/entity/living/LivingSwapItemsEvent.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.minecraftforge.event.entity.living;
+
+import net.minecraft.server.network.ServerGamePacketListenerImpl;
+import net.minecraft.world.entity.LivingEntity;
+import net.minecraft.world.item.ItemStack;
+import net.minecraftforge.eventbus.api.Cancelable;
+import org.jetbrains.annotations.ApiStatus;
+
+public class LivingSwapItemsEvent extends LivingEvent
+{
+
+    @ApiStatus.Internal
+    public LivingSwapItemsEvent(LivingEntity entity)
+    {
+        super(entity);
+    }
+
+    /**
+     * This event is fired when a living entity is about to swap the items in their main and offhand.
+     * This event is executed in {@link ServerGamePacketListenerImpl#handlePlayerAction}
+     *
+     * <p>This event is {@linkplain Cancelable cancellable}, and does not {@linkplain HasResult have a result}.
+     */
+    @Cancelable
+    public static class Hands extends LivingSwapItemsEvent
+    {
+        private ItemStack toMainHand;
+        private ItemStack toOffHand;
+
+        @ApiStatus.Internal
+        public Hands(LivingEntity entity)
+        {
+            super(entity);
+            this.toMainHand = entity.getOffhandItem(); //the main hand will be swapped with the offhand
+            this.toOffHand = entity.getMainHandItem(); //the offhand will be swapped with the main hand
+        }
+
+        /**
+         * Gets the item that will be swapped to the main hand of the entity.
+         * @return The item that will be swapped to the main hand.
+         */
+        public ItemStack getItemSwappedToMainHand()
+        {
+            return toMainHand;
+        }
+
+        /**
+         * Gets the item that will be swapped to the offhand of the entity.
+         * @return The item that will be swapped to the offhand.
+         */
+        public ItemStack getItemSwappedToOffHand()
+        {
+            return toOffHand;
+        }
+
+        /**
+         * Sets the item that will be swapped to the main hand of the entity.
+         * @param item The item to swap to the main hand.
+         */
+        public void setItemSwappedToMainHand(ItemStack item)
+        {
+            this.toMainHand = item;
+        }
+
+        /**
+         * Sets the item that will be swapped to the offhand of the entity.
+         * @param item The item to swap to the offhand.
+         */
+        public void setItemSwappedToOffHand(ItemStack item)
+        {
+            this.toOffHand = item;
+        }
+    }
+}