Added PlayerChangeHeldSlotEvent

src/main/java/net/minestom/server/event/player/PlayerChangeHeldSlotEvent.java

@@ -0,0 +1,49 @@
+package net.minestom.server.event.player;
+
+import net.minestom.server.entity.Player;
+import net.minestom.server.event.CancellableEvent;
+import net.minestom.server.utils.MathUtils;
+import net.minestom.server.utils.validate.Check;
+
+/**
+ * Called when a player change his held slot (by pressing 1-9 keys)
+ */
+public class PlayerChangeHeldSlotEvent extends CancellableEvent {
+
+    private Player player;
+    private short slot;
+
+    public PlayerChangeHeldSlotEvent(Player player, short slot) {
+        this.player = player;
+        this.slot = slot;
+    }
+
+    /**
+     * Get the player who changed his held slot
+     *
+     * @return the player
+     */
+    public Player getPlayer() {
+        return player;
+    }
+
+    /**
+     * Get the slot which the player will held
+     *
+     * @return the held slot
+     */
+    public short getSlot() {
+        return slot;
+    }
+
+    /**
+     * Change the final held slot of the player
+     *
+     * @param slot the new held slot
+     * @throws IllegalArgumentException if {@param slot} is not between 0 and 8
+     */
+    public void setSlot(short slot) {
+        Check.argCondition(!MathUtils.isBetween(slot, 0, 8), "The held slot needs to be between 0 and 8");
+        this.slot = slot;
+    }
+}

src/main/java/net/minestom/server/listener/PlayerHeldListener.java

@@ -1,18 +1,38 @@
 package net.minestom.server.listener;
 
 import net.minestom.server.entity.Player;
+import net.minestom.server.event.player.PlayerChangeHeldSlotEvent;
 import net.minestom.server.network.packet.client.play.ClientHeldItemChangePacket;
 import net.minestom.server.utils.MathUtils;
 
 public class PlayerHeldListener {
 
     public static void heldListener(ClientHeldItemChangePacket packet, Player player) {
-        short slot = packet.slot;
+        final short slot = packet.slot;
         if (!MathUtils.isBetween(slot, 0, 8)) {
             // Incorrect packet, ignore
             return;
         }
-        player.refreshHeldSlot(slot);
+
+        PlayerChangeHeldSlotEvent changeHeldSlotEvent = new PlayerChangeHeldSlotEvent(player, slot);
+        player.callEvent(PlayerChangeHeldSlotEvent.class, changeHeldSlotEvent);
+
+        if (!changeHeldSlotEvent.isCancelled()) {
+            // Event hasn't been canceled, process it
+
+            final short resultSlot = changeHeldSlotEvent.getSlot();
+
+            // If the held slot has been changed by the event, send the change to the player
+            if (resultSlot != slot) {
+                player.setHeldItemSlot(resultSlot);
+            } else {
+                // Otherwise, simply refresh the player field
+                player.refreshHeldSlot(resultSlot);
+            }
+        } else {
+            // Event has been canceled, send the last held slot to refresh the client
+            player.setHeldItemSlot(player.getHeldSlot());
+        }
     }
 
 }