Here's my code:

package com.jerrylu086.createarsenal.items;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Iterables;
import com.google.common.collect.Multimap;
import com.jerrylu086.createarsenal.CreateArsenal;
import com.jerrylu086.createarsenal.registry.ModItems;
import net.minecraft.entity.Entity;
import net.minecraft.entity.LivingEntity;
import net.minecraft.entity.ai.attributes.Attribute;
import net.minecraft.entity.ai.attributes.AttributeModifier;
import net.minecraft.inventory.EquipmentSlotType;
import net.minecraft.item.*;
import net.minecraft.util.DamageSource;
import net.minecraftforge.event.entity.living.LivingDamageEvent;
import net.minecraftforge.event.entity.living.LivingHurtEvent;
import net.minecraftforge.eventbus.api.SubscribeEvent;
import net.minecraftforge.fml.common.Mod.EventBusSubscriber;

import javax.annotation.Nonnull;

@EventBusSubscriber(modid = CreateArsenal.MOD_ID)
public class ExoframeItem extends ArmorItem {

    private Multimap<Attribute, AttributeModifier> attributeModifiers = ArrayListMultimap.create();

    public ExoframeItem(IArmorMaterial materialIn, EquipmentSlotType slot, Properties properties) {
        super(materialIn, slot, properties);
    }

    /*@Override
    public boolean hitEntity(@Nonnull ItemStack stack, @Nonnull LivingEntity target, @Nonnull LivingEntity attacker) {
        stack.damageItem(1, attacker, (entity) -> {
            entity.sendBreakAnimation(EquipmentSlotType.CHEST);
        });
        return true;
    }*/

    @SubscribeEvent
    public void onDamageDealt (LivingDamageEvent event) {

        Entity trueSource = event.getSource().getTrueSource();

        for (ItemStack stack : trueSource.getArmorInventoryList()) {

            if (isExo(stack)) {

                float damage = event.getAmount() + 5;
                event.setAmount(damage);

            }
        }
    }

    public boolean isExo(ItemStack stack) {

        if (stack == null || stack.getItem() == null) {

            return false;
        }

        Item item = stack.getItem();
        return item == ModItems.EXOFRAME.get();
    }
}

What I want to do is when this event detects an attacker of LivingDamageEvent is wearing the Exoframe item will increase the attack damage by 5 (can be reduced so use LivingDamageEvent instead of LivingHurtEvent). But I tested it, it does not do anything when I'm wearing the item. How I fix it?

8 hours ago, diesieben07 said:

• @EventBusSubscriber registers the Class to the event bus, which checks static methods only.
• Why is this not just an attack damage attribute modifier on your item? Then you don't need the event handler at all. This is exactly what attribute modifiers are for...

I used the AttributeModifer before, but what I want is increase the attack damage. Like if I'm using melee damage and wearing the chestplate, I will deal 6 damage. And if I'm using netherite sword, which has 8 attack damage, I will deal 13 damage. As far as I know what I can do with AttributeModifer is only *set* the attack damage, like if I'm wearing the chestplate, I will always deal 5 damage, even I'm using the weapons with high attack damage.