GodotTutorials/Inventory/CSharp/InventorySlot.cs

using Godot;
using Godot.Collections;
using System;
using System.Linq;

public partial class InventorySlot : Panel
{
	[Export] public TextureRect IconRect;
	[Export] public Label CountLabel;

	public InventorySlotData SlotData;
	public int SlotIndex;
	public Inventory Inventory;

	// Refresh the current slot with the data of it's inventory slot
	public void Refresh()
	{
		if (SlotIndex < Inventory.Slots.Count())
		{
			SlotData = Inventory.Slots[SlotIndex];
		}

		if (SlotData == null)
		{
			IconRect.Texture = null;
			CountLabel.Text = "";
		}
		else
		{
			IconRect.Texture = SlotData.Item.Icon;
			CountLabel.Text = (SlotData.Count > 1) ? SlotData.Count.ToString() : "";
		}
	}

	// Handle Item being dragged elsewhere
    public override Variant _GetDragData(Vector2 atPosition)
    {
		if (SlotData == null)
			return default;

		// Create a preview of the item being dragged
		var preview = new TextureRect { Texture = SlotData.Item.Icon, CustomMinimumSize = new Vector2(32f, 32f) };
		SetDragPreview(preview);

		var data = new Dictionary { { "from_slot", SlotIndex } };
		return data;
    }

	// Can we drop the item where we are?
    public override bool _CanDropData(Vector2 atPosition, Variant data)
    {
		return data.VariantType == Variant.Type.Dictionary
			&& ((Dictionary)data).ContainsKey("from_slot");
    }

    public override void _DropData(Vector2 atPosition, Variant data)
    {
		int fromIndex = (int)((Dictionary)data)["from_slot"];

		// Swap the 2 indexes
		(Inventory.Slots[SlotIndex], Inventory.Slots[fromIndex]) = (Inventory.Slots[fromIndex], Inventory.Slots[SlotIndex]);

		// Call the refresh method for all objects that belong in the inventory_slots group
		GetTree().CallGroup("inventory_slots_cs", InventorySlot.MethodName.Refresh);
    }

	public void InitializeSlot(int slotIndex, Inventory inventory)
	{
		SlotIndex = slotIndex;
		Inventory = inventory;

		Refresh();
	}
}