Sample GTM selection factory to pre-populate category selection options (Episerver Forms demo).

GtmCategorySelectionFactory.cs

using EPiServer.Shell.ObjectEditing;
using System.Collections.Generic;

namespace AlloyWithFind.Business.SelectionFactories
{
    /// <summary>
    /// Selection factory to return GTM category values for form submission event.
    /// </summary>
    public class GtmCategorySelectionFactory : ISelectionFactory
    {
        /// <summary>
        /// Gets the GTM category values.
        /// </summary>
        /// <param name="metadata"></param>
        /// <returns>GTM category values</returns>
        public IEnumerable<ISelectItem> GetSelections(ExtendedMetadata metadata)
        {
            // not localized for now
            return new List<ISelectItem>
            {
                new SelectItem{ Text = "CustomerProfile", Value = "customerprofile"},
                new SelectItem{ Text = "Commercial", Value = "commercial"},
                new SelectItem{ Text = "Other", Value = "other"}
            };
        }
    }
}