Base class for a Unity property drawer for structures like "quantity" of "thing"

ItemQuantityPropertyDrawer.cs

using UnityEditor;
using UnityEngine;

// Author: Brian MacIntosh (The Periodic Group)
// MIT License

/// <summary>
/// Base class that can be extended to quickly create a property drawer for a structure containing
/// data like "quantity" of "thing".
/// </summary>
public abstract class ItemQuantityPropertyDrawer : PropertyDrawer
{
	/// <summary>
	/// Name of the quantity/stack size property.
	/// </summary>
	public abstract string QuantityPropName { get; }

	/// <summary>
	/// Name of the item/object property.
	/// </summary>
	public abstract string ItemPropName { get; }

	public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
	{
		EditorGUI.BeginProperty(position, label, property);

		position = EditorGUI.PrefixLabel(position, GUIUtility.GetControlID(FocusType.Passive), label);

		int indent = EditorGUI.indentLevel;
		EditorGUI.indentLevel = 0;

		Rect quantityPosition = position;
		quantityPosition.width = 40f;
		Rect resourcePosition = position;
		resourcePosition.xMin += quantityPosition.width + 4f;
		EditorGUI.PropertyField(quantityPosition, property.FindPropertyRelative(QuantityPropName), GUIContent.none);
		EditorGUI.PropertyField(resourcePosition, property.FindPropertyRelative(ItemPropName), GUIContent.none);

		EditorGUI.indentLevel = indent;

		EditorGUI.EndProperty();
	}
}