Example of a UI Toolkit custom binding for Addressables (2023.3)

AddressablesBinding.cs

using UnityEngine;
using UnityEngine.AddressableAssets;
using UnityEngine.ResourceManagement.AsyncOperations;
using UnityEngine.UIElements;

#if UNITY_EDITOR
public class AssetReferenceConverter<T> : UnityEditor.UIElements.UxmlAttributeConverter<AssetReferenceT<T>> where T : Object
{
    public override AssetReferenceT<T> FromString(string value)
    {
        var split = value.Split('#');
        return new AssetReferenceT<T>(split[0]){ SubObjectName = split[1] };
    }
    
    public override string ToString(AssetReferenceT<T> value)
    {
        return $"{value.AssetGUID}#{value.SubObjectName}";
    }
}
#endif

// Our concrete class for Texture2D
[UxmlObject]
public partial class Texure2DAddressablesBinding : AddressablesBinding<Texture2D>
{ }

[UxmlObject]
public partial class SpriteAddressablesBinding : AddressablesBinding<Sprite>
{ }

// Our generic class for any Object. A concrete class is needed for each to be used in UXML.
[UxmlObject]
public partial class AddressablesBinding<T> : CustomBinding where T: Object
{
    [UxmlAttribute]
    public AssetReferenceT<T> AssetReference { get; set; }

    [UxmlAttribute]
    public bool Synchronous { get; set; }

    public AddressablesBinding()
    {
        updateTrigger = BindingUpdateTrigger.WhenDirty;
    }

    protected override void OnDeactivated(in BindingActivationContext context)
    {
        if (AssetReference.OperationHandle.IsValid())
            AssetReference.ReleaseAsset();
        base.OnDeactivated(context);
    }

    protected override BindingResult Update(in BindingContext context)
    {
        if (!AssetReference.OperationHandle.IsValid())
        {
            AssetReference.LoadAssetAsync<T>();
            if (!AssetReference.OperationHandle.IsDone && Synchronous)
                AssetReference.OperationHandle.WaitForCompletion();
        }

        if (!AssetReference.OperationHandle.IsDone)
            return new BindingResult(BindingStatus.Pending);
        if (AssetReference.OperationHandle.Status == AsyncOperationStatus.Failed)
            return new BindingResult(BindingStatus.Failure, AssetReference.OperationHandle.OperationException?.ToString());

        var element = context.targetElement;
        if (ConverterGroups.TrySetValueGlobal(ref element, context.bindingId, AssetReference.OperationHandle.Result as T, out var errorCode))
            return new BindingResult(BindingStatus.Success);
        else
            return new BindingResult(BindingStatus.Failure, errorCode.ToString());
    }
}