Alchemy/docs/articles/en/creating-custom-attribute.md

Creating Custom Attributes

By using AlchemyAttributeDrawer, it is possible to create custom attributes that work within Alchemy. Here is an example demonstrating the implementation of HelpBoxAttribute and its corresponding drawer.

First, define the attribute to be added to fields or properties.

using System;
using UnityEngine.UIElements;

public sealed class HelpBoxAttribute : Attribute
{
    public HelpBoxAttribute(string message, HelpBoxMessageType messageType = HelpBoxMessageType.Info)
    {
        Message = message;
        MessageType = messageType;
    }

    public string Message { get; }
    public HelpBoxMessageType MessageType { get; }
}

Next, create the drawer corresponding to the defined attribute. Drawer scripts should be placed within the Editor folder.

using UnityEngine.UIElements;
using Alchemy.Editor;

[CustomAttributeDrawer(typeof(HelpBoxAttribute))]
public sealed class HelpBoxDrawer : AlchemyAttributeDrawer
{
    HelpBox helpBox;

    public override void OnCreateElement()
    {
        var att = (HelpBoxAttribute)Attribute;
        helpBox = new HelpBox(att.Message, att.MessageType);

        var parent = TargetElement.parent;
        parent.Insert(parent.IndexOf(TargetElement), helpBox);
    }
}

Implement the OnCreateElement() method to add processing when creating the corresponding VisualElement for the member. Unlike regular PropertyDrawers that override the drawing process, here we're adding post-processing after the creation of the Visual Element. This mechanism allows Alchemy to combine multiple drawers.

Additionally, make sure to add the CustomAttributeDrawer attribute to the defined drawer, with the type of the defined attribute as an argument. Alchemy uses this attribute to search for the necessary drawers for element rendering.