PropertyDataDataSource.cs

using System.Collections.Generic;
using System.Linq;
using Umbraco.Community.Contentment.DataEditors;
using Umbraco.Core.PropertyEditors;
using Umbraco.Web;

namespace MyWebsite.DataSources
{
    public class PropertyDataDataSource : IDataListSource
    {
        private readonly IUmbracoContextAccessor _umbracoContextAccessor;

        public PropertyDataDataSource(IUmbracoContextAccessor umbracoContextAccessor)
        {
            _umbracoContextAccessor = umbracoContextAccessor;
        }

        public string Name => "Umbraco Property Data";

        public string Description => "Data source for umbraco property data coming from the website root node.";

        public string Icon => "icon-globe";

        public OverlaySize OverlaySize => OverlaySize.Small;

        public Dictionary<string, object> DefaultValues => new Dictionary<string, object>();

        public IEnumerable<ConfigurationField> Fields => new ConfigurationField[]
        {
            new ConfigurationField
            {
                Key = "propAlias",
                Name = "Property",
                Description = "Select the property to populate the data source with.",
                View = "~/umbraco/views/propertyeditors/entitypicker/entitypicker.html",
                Config = new Dictionary<string, object>
                {
                    { "multiple", "0" },
                    { "entityType", "PropertyType" },
                    { "publishBy", "alias" },
                }
            }
        };

        public IEnumerable<DataListItem> GetItems(Dictionary<string, object> config)
        {
            if (config.TryGetValue("propAlias", out var tmp) && tmp is string alias && string.IsNullOrWhiteSpace(alias) == false)
            {
                var content = _umbracoContextAccessor.UmbracoContext.Content.GetAtRoot().First();
                if (content != null)
                {
                    var propertyValue = content.Value<string[]>(alias);
                    if (propertyValue != null)
                    {
                        return propertyValue.Select(x => new DataListItem { Name = x, Value = x });
                    }
                }
            }

            return Enumerable.Empty<DataListItem>();
        }
    }
}

Thanks @leekelleher as of course I just needed the umbraco/ in the view path. Good job @greystate isn't paying me for this, otherwise that might have been embarrassing 😆

I still get an error but I now see that's from the Config dictionary field property (as lifted from v8), so I can make progress with investigating that now. I think I was thinking this might be a problem caused by RCLs or something... But clearly not! 🙏