Unity Inventory System

A SOLID-principle-based inventory system for Unity games featuring drag-and-drop functionality, item stacking, splitting, and merging capabilities.

Features

• Mouse-based drag-and-drop item management
• Automatic stacking of identical items up to maximum stack size
• Right-click stack splitting
• Automatic item merging and slot swapping
• Hover tooltips for item details
• Modular architecture built using ScriptableObjects
• Unity Netcode integration ready

Dependencies

Unity Version

• Unity 2022.3 LTS or higher

Required Packages

• TextMeshPro (com.unity.textmeshpro: 3.0.6)
• Netcode for GameObjects (com.unity.netcode.gameobjects: 1.7.1)

Installation via Package Manager

1. Open Unity Package Manager (Window > Package Manager).
2. Install TextMeshPro from the Unity Registry.
3. Install Netcode for GameObjects from the Unity Registry.

Project Structure

Assets/
├── Scripts/
│   ├── Core/
│   │   ├── ItemDefinition.cs
│   │   ├── ItemContainerConfig.cs
│   │   └── ItemContainerSlotUIConfig.cs
│   ├── Inventory/
│   │   ├── ItemContainer.cs
│   │   ├── ItemContainerItemUI.cs
│   │   └── ItemContainerSlotUI.cs
│   ├── DragSystem/
│   │   ├── ItemDragManager.cs
│   │   ├── InventoryInputHandler.cs
│   │   ├── ItemDragService.cs
│   │   ├── ItemOperationService.cs
│   │   └── DragVisualizer.cs
│   └── UI/
│       └── TooltipUI.cs
├── Prefabs/
│   ├── InventoryContainer.prefab
│   ├── InventorySlot.prefab
│   └── ItemDragManager.prefab
└── ScriptableObjects/
    ├── Items/
    │   ├── Sword.asset
    │   ├── Shield.asset
    │   └── Potion.asset
    └── Configs/
        ├── DefaultContainerConfig.asset
        └── DefaultSlotConfig.asset

Quick Start

1. Setup Item Definitions

Create item assets using Assets > Create > Inventory System > Item. Configure the ID, Name, Description, Icon, Max Stack Size, and Prefab.

2. Create Inventory Container

1. Create an empty GameObject in your scene.
2. Add the ItemContainer component.
3. Assign an ItemContainerConfig.
4. Add ItemContainerSlotUI components as child objects.
5. Reference the slots inside the Slots list on the ItemContainer.

3. Setup Drag Manager

1. Add the ItemDragManager prefab to the scene.
2. Attach the DragVisualizer component.
3. Assign the visual UI elements (Image, Text).

4. Configure UI Elements

Each slot requires:

• ItemContainerSlotUI component
• Background Image
• Item Display Image
• TextMeshProUGUI element for stack counts

Usage Examples

Adding Items to Inventory

public class InventoryManager : MonoBehaviour
{
    [SerializeField] private ItemContainer playerInventory;
    [SerializeField] private ItemDefinition swordItem;
    
    private void Start()
    {
        playerInventory.TryAddItem(swordItem, 5);
    }
}

Custom Item Operations

public class CustomItemOperations : MonoBehaviour, IItemOperationService
{
    public bool TryMoveItem(ItemContainerItemUI item, ItemContainerSlotUI targetSlot)
    {
        if (item.ItemDefinition.ItemType == ItemType.Weapon && targetSlot.SlotType != SlotType.WeaponSlot)
        {
            return false;
        }
            
        return defaultOperationService.TryMoveItem(item, targetSlot);
    }
}

Customization

• Item Definitions: Right-click in Project view -> Create > Inventory System > Item.
• Slot Visuals: Configure active/passive slot sprites in ItemContainerSlotUIConfig.
• Drag UI: Customize the drag layer appearance in DragVisualizer.
• Tooltips: Extend TooltipUI to adjust tooltip layouts or content.

Architecture Overview

The system strictly follows SOLID principles:

• Single Responsibility: Individual services handle input, drag state, visuals, and container logic separately.
• Open/Closed & Dependency Inversion: Behaviors rely on interfaces (IItemOperationService, IItemDragService), allowing core logic changes without modifying existing components.

Component	Responsibility
ItemDragService	Manages drag state
ItemOperationService	Handles item logic and stack operations
DragVisualizer	Handles visual representation during dragging
InventoryInputHandler	Processes input events
ItemDragManager	Acts as the primary facade coordinator

Testing

[Test]
public void TestItemMerging()
{
    var mockDragService = new Mock<IItemDragService>();
    var operationService = new ItemOperationService();
    
    Assert.IsTrue(operationService.TryMergeItems(item1, slot));
}

Requirements

• Unity 2022.3 LTS or higher
• TextMeshPro
• Unity Netcode for GameObjects (optional)
• C# 9.0+ support

License

This project is licensed under the MIT License.