PropertyAttribute.applyToCollection

Description

Makes attribute affect collections instead of their items.

When you apply a PropertyAttribute to a collection, by default Unity applies it to each element of the collection. When applyToCollection is true, the attribute is applied to the collection itself instead.

You can use this in scenarios where the attribute functionality needs to apply to the collection as a whole rather than per element. Some typical scenarios include:

• A reorderable list header or collection-level label. For example, when creating a drawer that adds a summary line stating the total number of items in the list, or a custom add or remove toolbar.
• An attribute that makes a list non-reorderable, or locks its size.
• Validation across the collection. For example, an attribute that checks that a list contains unique entries or that it has at least three items.

using UnityEditor;
using UnityEditor.UIElements;
using UnityEngine;
using UnityEngine.UIElements;

public class Collection : MonoBehaviour
{
    public int before;
    [GreenCollectionDrawer] public int[] collection;
    public int after;
}

public class GreenCollectionDrawerAttribute : PropertyAttribute
{
    public GreenCollectionDrawerAttribute() : base(true) { }
}

[CustomPropertyDrawer(typeof(GreenCollectionDrawerAttribute))]
public class GreenCollectionDrawer : PropertyDrawer
{
    public override VisualElement CreatePropertyGUI(SerializedProperty property)
    {
        return new PropertyField(property)
        {
            style =
            {
                backgroundColor = Color.green
            }
        };
    }
}