Inventory Checks

Custom usable items might have varying restrictions, and it will be hard to enforce a consistent standard for that kind of stuff. That's why RogueLibs introduces special inventory checks, that will run before and after any usable/combinable/targetable items in the game. You can use these checks to prevent the item's intended function, or maybe somehow augment it.

InventoryChecks

With inventory checks, you can omit code like this:

if (Owner.statusEffects.hasTrait("BloodRestoresHealth"))
{
    Owner.SayDialogue("WontEatThis");
    return;
}
if (Owner.statusEffects.hasTrait("OilRestoresHealth"))
{
    Owner.SayDialogue("WontEatThat");
    return;
}
if (Owner.health == Owner.maxHealth)
{
    Owner.SayDialogue("NoImFull");
    return;
}
...

These inventory checks can also implement some common side effects, that modders sometimes forget to implement. For example, removing an item from the inventory or stopping the interaction, when the item's count reaches 0 (RogueLibs provides these checks).

Ignoring inventory checks

Inventory checks can be ignored by using an IgnoreChecks attribute.

You can put IgnoreChecks attributes on your item's class or on any of the interface methods.

[ItemCategories(RogueCategories.Food, RogueCategories.Weird, "Meat")]
public class MysteryFood : CustomItem, IItemUsable
{
    [IgnoreChecks("VegetarianCheck")]
    public bool UseItem()
    {
        e.User.ChangeHealth(Item.healthChange);
        Count--;
        e.User.Say("Huh, tasty. I wonder what that was..."); // O_o
        return true;
    }
}

See the table of inventory checks implemented by RogueLibs later on this page.

Adding inventory checks

RogueEventArgs class has two properties: Cancel and Handled. If you set Handled to true, then all other checks will be skipped. If you set Cancel to true, then the action that was going to happen will not happen. Usually, they are set to true at the same time.

For example, there's a trait called "Vegetarian" that should prohibit the player from consuming food with "Meat" category:

InventoryChecks.AddItemUsingCheck("VegetarianCheck", VegetarianCheck);
...
public static void VegetarianCheck(OnItemUsingArgs e)
{
    if (e.Item.itemType == ItemTypes.Food && e.User.HasTrait("Vegetarian") && e.Item.Categories.Contains("Meat"))
    {
        // do something to indicate why the item cannot be used
        e.User.gc.audioHandler.Play(e.User, "CantDo");
        e.User.SayDialogue("WontEatMeat");
        // set Cancel and Handled to true
        e.Cancel = e.Handled = true;
    }
};

If you want to override an inventory check from another mod, then you'll have to patch it with Harmony.

Table of default checks

IItemUsable checks

Name	Criteria	Dialogue
Ghost	Player is a ghost.	-
PeaBrained	"Pea-Brained" trait, NOT Food type.	"GRRRRRRRR!!!!!"
OnlyOil	"Oil Reliant" trait, Food type and (Food or Alcohol category).	"I'm gonna need some oil..."
OnlyOilMedicine	"Oil Reliant" trait, Consumable type and Health category.	"I'm gonna need some oil..."
OnlyBlood	"Jugularious" trait, Food type and (Food or Alcohol category).	"Ew gross, I'm not putting that in my mouth!"
OnlyBloodMedicine	"Jugularious" trait, Consumable type and Health category.	"Modern medicine is for humans, I want BLOOD!"
OnlyCharge	"Electronic" trait, Food type and Food category.	"I don't exactly have a stomach."
OnlyHumanFlesh	"Strict Cannibal" trait, Food type and Food category.	"Ew gross, I'm not putting that in my mouth!"
FullHealth	Player's health is full and the item's healthChange is greater than 0.	"No need, I'm feelin' good!"

These checks are exposed via DefaultInventoryChecks. The rest are implemented inside RogueLibs' patches.

IItemCombinable checks

Name	Criteria	What will happen
AutoStacking	Items have the same name	They will be highlighted, and once combined, they will be stacked together
StopOnZero	The current item's count is 0, or it's no longer in the inventory	Interaction/combining will be stopped

IItemTargetable checks

Name	Criteria	What will happen
Distance	The target object is over 15 units away	false
ButlerBot	The target is a Butler Bot	false
EmptyMech	The target is an Empty Mech	false
StopOnZero	The current item's count is 0, or it's no longer in the inventory	Interaction/targeting will be stopped