Unity Project Guide: Build Pickups, Inventory Slots, and a Hotbar

Inventory systems become confusing when beginners try to build everything at once: drag-and-drop, equipment, crafting, shops, storage chests, item rarity, icons, tooltips, and saving.

This guide builds a smaller but useful version:

• Items are defined with ScriptableObjects.
• The player can pick up items.
• Inventory slots can stack items.
• Number keys select a hotbar slot.
• The selected slot can be consumed.

This gives you a foundation you can extend without rewriting everything.

Step 1: Create the Item Definition

Create a folder:

1Assets/Items

Create ItemDefinition.cs.

1using UnityEngine;2 3[CreateAssetMenu(menuName = "Game/Item Definition")]4public class ItemDefinition : ScriptableObject5{6    public string itemId;7    public string displayName;8    public Sprite icon;9    public int maxStack = 1;10    public bool consumable;11}

In Unity:

1. Right-click in Assets/Items.
2. Choose Create > Game > Item Definition.
3. Name it Apple.
4. Set:
   • Item Id: apple
   • Display Name: Apple
   • Max Stack: 10
   • Consumable: enabled

Why ScriptableObjects? They let designers create item data in the editor without hardcoding every item in a script.

Step 2: Create an Inventory Slot Model

Create InventorySlot.cs.

1[System.Serializable]2public class InventorySlot3{4    public ItemDefinition item;5    public int quantity;6 7    public bool IsEmpty => item == null || quantity <= 0;8 9    public void Clear()10    {11        item = null;12        quantity = 0;13    }14}

This is not a MonoBehaviour. It is plain data.

Step 3: Create the Inventory Component

Create PlayerInventorySlots.cs.

1using System;2using UnityEngine;3 4public class PlayerInventorySlots : MonoBehaviour5{6    [SerializeField] private int slotCount = 8;7 8    public InventorySlot[] Slots { get; private set; }9    public int SelectedIndex { get; private set; }10 11    public event Action InventoryChanged;12    public event Action<int> SelectionChanged;13 14    private void Awake()15    {16        Slots = new InventorySlot[slotCount];17        for (int i = 0; i < Slots.Length; i++)18        {19            Slots[i] = new InventorySlot();20        }21    }22 23    public bool TryAdd(ItemDefinition item, int amount)24    {25        if (item == null || amount <= 0) return false;26 27        amount = AddToExistingStacks(item, amount);28        amount = AddToEmptySlots(item, amount);29 30        InventoryChanged?.Invoke();31        return amount == 0;32    }33 34    private int AddToExistingStacks(ItemDefinition item, int amount)35    {36        for (int i = 0; i < Slots.Length; i++)37        {38            InventorySlot slot = Slots[i];39            if (slot.IsEmpty) continue;40            if (slot.item != item) continue;41            if (slot.quantity >= item.maxStack) continue;42 43            int room = item.maxStack - slot.quantity;44            int toAdd = Mathf.Min(room, amount);45            slot.quantity += toAdd;46            amount -= toAdd;47 48            if (amount == 0) return 0;49        }50 51        return amount;52    }53 54    private int AddToEmptySlots(ItemDefinition item, int amount)55    {56        for (int i = 0; i < Slots.Length; i++)57        {58            InventorySlot slot = Slots[i];59            if (!slot.IsEmpty) continue;60 61            int toAdd = Mathf.Min(item.maxStack, amount);62            slot.item = item;63            slot.quantity = toAdd;64            amount -= toAdd;65 66            if (amount == 0) return 0;67        }68 69        return amount;70    }71 72    public void SelectSlot(int index)73    {74        if (index < 0 || index >= Slots.Length) return;75        SelectedIndex = index;76        SelectionChanged?.Invoke(SelectedIndex);77    }78 79    public void UseSelected()80    {81        InventorySlot slot = Slots[SelectedIndex];82        if (slot.IsEmpty) return;83        if (!slot.item.consumable) return;84 85        Debug.Log($"Used {slot.item.displayName}");86 87        slot.quantity -= 1;88        if (slot.quantity <= 0)89        {90            slot.Clear();91        }92 93        InventoryChanged?.Invoke();94    }95}

Attach this script to the Player.

Step 4: Create Pickup Objects

Create a sprite in the scene called ApplePickup.

Add:

• CircleCollider2D
• Enable Is Trigger

Create ItemPickup.cs.

1using UnityEngine;2 3public class ItemPickup : MonoBehaviour4{5    [SerializeField] private ItemDefinition item;6    [SerializeField] private int quantity = 1;7 8    private void OnTriggerEnter2D(Collider2D other)9    {10        PlayerInventorySlots inventory = other.GetComponent<PlayerInventorySlots>();11        if (inventory == null) return;12 13        bool fullyAdded = inventory.TryAdd(item, quantity);14        if (fullyAdded)15        {16            Destroy(gameObject);17        }18        else19        {20            Debug.Log("Inventory full.");21        }22    }23}

Attach it to ApplePickup and assign the Apple item definition.

Now the player can pick up apples.

Step 5: Add Hotbar Input

Create HotbarInput.cs.

1using UnityEngine;2 3public class HotbarInput : MonoBehaviour4{5    private PlayerInventorySlots inventory;6 7    private void Awake()8    {9        inventory = GetComponent<PlayerInventorySlots>();10    }11 12    private void Update()13    {14        for (int i = 0; i < inventory.Slots.Length; i++)15        {16            KeyCode key = KeyCode.Alpha1 + i;17            if (Input.GetKeyDown(key))18            {19                inventory.SelectSlot(i);20            }21        }22 23        if (Input.GetKeyDown(KeyCode.E))24        {25            inventory.UseSelected();26        }27    }28}

Attach it to the Player.

Now number keys select slots, and E uses the selected consumable.

Step 6: Build a Simple Hotbar UI

Create a Canvas and add a horizontal layout:

1. Right-click Canvas.
2. Create UI > Panel.
3. Rename it Hotbar.
4. Add Horizontal Layout Group.
5. Create 8 child panels or buttons for slots.

For each slot, add:

• An Image for the icon.
• A TextMeshPro label for quantity.
• A border or background image for selection.

Create HotbarSlotUI.cs.

1using TMPro;2using UnityEngine;3using UnityEngine.UI;4 5public class HotbarSlotUI : MonoBehaviour6{7    [SerializeField] private Image icon;8    [SerializeField] private TMP_Text quantityText;9    [SerializeField] private GameObject selectedFrame;10 11    public void Render(InventorySlot slot, bool selected)12    {13        selectedFrame.SetActive(selected);14 15        if (slot.IsEmpty)16        {17            icon.enabled = false;18            quantityText.text = "";19            return;20        }21 22        icon.enabled = true;23        icon.sprite = slot.item.icon;24        quantityText.text = slot.quantity > 1 ? slot.quantity.ToString() : "";25    }26}

Create HotbarUI.cs.

1using UnityEngine;2 3public class HotbarUI : MonoBehaviour4{5    [SerializeField] private PlayerInventorySlots inventory;6    [SerializeField] private HotbarSlotUI[] slots;7 8    private void OnEnable()9    {10        inventory.InventoryChanged += Render;11        inventory.SelectionChanged += _ => Render();12        Render();13    }14 15    private void OnDisable()16    {17        inventory.InventoryChanged -= Render;18        inventory.SelectionChanged -= _ => Render();19    }20 21    private void Render()22    {23        for (int i = 0; i < slots.Length; i++)24        {25            slots[i].Render(inventory.Slots[i], i == inventory.SelectedIndex);26        }27    }28}

Important: the unsubscribe shown above with _ => Render() creates a new delegate, so in production you should use named methods. For a cleaner version:

1private void OnSelectionChanged(int index) => Render();

Then subscribe and unsubscribe with OnSelectionChanged.

Step 7: Test the System

Use this checklist:

• Picking up one apple creates a stack.
• Picking up several apples increases quantity.
• Quantity stops at max stack and moves to another slot.
• If all slots are full, pickup remains in the world.
• Pressing number keys changes selection.
• Pressing E consumes the selected apple.
• Empty slots render as empty UI.

Step 8: Common Beginner Mistakes

• Do not compare items by display name. Use the ScriptableObject reference or a stable item id.
• Do not put all inventory code inside UI buttons.
• Do not destroy pickups unless the item was actually added.
• Do not save Sprite references directly in save files. Save item ids instead.

Where To Go Next

Next upgrades:

• Add non-consumable items like keys.
• Add equipment slots.
• Save inventory to JSON.
• Add drag-and-drop later, after the data model works.
• Add item tooltips.

The main lesson is separation: item definitions describe what an item is, inventory slots describe what the player owns, and UI only renders the current state.