Inserting into the first available inventory slot

Question

Hello my inventory system picks up one item but does not pickup any more to fill the other two slots. It is saying the whole inventory is full when it should be one slot is full. Here is my code for the inventory and this is attached to the player.

public class MedInventory : MonoBehaviour
{
    public bool[] isFull;
    public GameObject[] MedkitSlot;
    public GameObject[] BandageSlot;
    public GameObject[] CoffeeSlot;
}

This next script is attached to the items you pickup.

    public class MedPickup : MonoBehaviour
{
    private MedInventory medInv;
    public GameObject itemButton;
    private void Start()
    {
        medInv = GameObject.FindGameObjectWithTag("Player").GetComponent<MedInventory>();
        itemButton.SetActive(false);
    }

    void OnTriggerStay2D(Collider2D other)
    {
        if (other.CompareTag("Player"))
        {
            GameObject[] targetSlot = new GameObject[0];
            bool validItem = true;

            switch (gameObject.tag)
            {
                case "medkit": targetSlot = medInv.MedkitSlot; break;
                case "bandage": targetSlot = medInv.BandageSlot; break;
                case "coffee": targetSlot = medInv.CoffeeSlot; break;
                default: validItem = false; break;
            }

            if (validItem)
            {
                for (int i = 0; i < targetSlot.Length; ++i)
                {
                    if (!medInv.isFull[i])
                    {
                        medInv.isFull[i] = true;
                        itemButton.SetActive(true);
                        Instantiate(itemButton, targetSlot[i].transform, false);
                        Destroy(gameObject);
                        break;
                    }
                }
            }
        }
    }
}

Answer 1

First, let's simplify your pickup. We'll use an enumeration to denote our various inventory item types, so we're not constrained by the tag system and don't need to do messy string marshalling and comparisons.

public enum InventoryItemType : int {
    Medkit,
    Bandage,
    Coffee
}

Now your pickup class can be a "Plain Old Data Structure" - a coffee cup takes no actions on its own, so it needs no methods.

public class Pickup : MonoBehaviour {
    public InventoryItemType type;
    public RectTransform inventoryButtonPrefab;
}

Notice how now, we don't need every pickup in the game to hold a reference to the inventory UI - that's not the coffee cup's job!

The inventory can be managed in one place, by a script on the player character. (Or on each player character, allowing you to support multiplayer. Or you could allow NPCs to pick up items, etc. - much more flexibility this way)

public class PlayerInventory : MonoBehaviour {
    // For convenience, let's make a type that bundles together
    // the UI slot for our inventory item, and the item that's in it.
    [System.Serializable]
    public struct InventorySlot {
        public RectTransform container;
        public RectTransform contents;
    }

    public InventorySlot[] MedkitSlots;
    public InventorySlot[] BandageSlots;
    public InventorySlot[] CoffeeSlots;

    void OnTriggerEnter2D(Collider2D other) {
        // We test whether this object has the component we care about,
        // so it's free to use tags for other purposes.
        if(!other.TryGetComponent(out Pickup pickup))
            return;

        // No need to initialize this with a value we're about to overwrite anyway.
        InventorySlot[] inventory;
        switch(pickup.type) {
            case InventoryItemType.Medkit:  inventory = MedkitSlots;  break;
            case InventoryItemType.Bandage: inventory = BandageSlots; break;
            case InventoryItemType.Coffee:  inventory = CoffeeSlots;  break;
            default: 
                Debug.LogErrorFormat("Unknown pickup type {0}", pickup.type);
                return;
        }

        for(int i = 0; i < inventory.Length; i++) {
            var slot = inventory[i];
            if(slot.contents != null)
                continue;

            slot.contents = Instantiate(pickup.inventoryButtonPrefab, slot.container, false);
            inventory[i] = slot; // Save our modifications to this slot.
            Destroy(other.gameObject);
            return;
        }

        Debug.LogFormat("Can't pick up {0}, inventory slots all full.", pickup.name);
    }
}