fix 1.21 InventoryView changes

bukkit-utils/src/main/java/net/anweisen/utilities/bukkit/utils/menu/MenuPositionListener.java

@@ -1,5 +1,6 @@
 package net.anweisen.utilities.bukkit.utils.menu;
 
+import net.anweisen.utilities.bukkit.utils.misc.CompatibilityUtils;
 import org.bukkit.entity.HumanEntity;
 import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
@@ -26,7 +27,7 @@ public void onClick(@Nonnull InventoryClickEvent event) {
 		Inventory inventory = event.getClickedInventory();
 		if (inventory == null) return;
 
-		if (inventory == event.getView().getTopInventory()) {
+		if (inventory == CompatibilityUtils.getTopInventory(event)) {
 
 			if (inventory.getHolder() != MenuPosition.HOLDER) return; // No menu inventory
 

bukkit-utils/src/main/java/net/anweisen/utilities/bukkit/utils/misc/CompatibilityUtils.java

@@ -0,0 +1,49 @@
+package net.anweisen.utilities.bukkit.utils.misc;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import javax.annotation.Nonnull;
+import net.anweisen.utilities.common.logging.ILogger;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/*
+ * In API version 1.20.6 and earlier, InventoryView is an abstract class
+ * In API version 1.21, InventoryView is an interface
+ */
+public class CompatibilityUtils {
+
+  protected static final ILogger logger = ILogger.forThisClass();
+  private static final Logger log = LoggerFactory.getLogger(CompatibilityUtils.class);
+
+  private CompatibilityUtils() {
+  }
+
+  public static Inventory getTopInventory(@Nonnull Player player) {
+    InventoryView view = player.getOpenInventory();
+
+    try {
+      Method getTopInventory = InventoryView.class.getMethod("getTopInventory");
+      return (Inventory) getTopInventory.invoke(view);
+    } catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException ex) {
+      logger.error("Failed to get top inventory", ex);
+      return null;
+    }
+  }
+
+  public static Inventory getTopInventory(@Nonnull InventoryClickEvent event) {
+    InventoryView view = event.getView();
+
+    try {
+      Method getTopInventory = InventoryView.class.getMethod("getTopInventory");
+      return (Inventory) getTopInventory.invoke(view);
+    } catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException ex) {
+      logger.error("Failed to get top inventory", ex);
+      return null;
+    }
+  }
+}