Get the Item selected in a Grouped Droplist Sitecore Field

FollowGroupedDroplist.cs

public class FollowGroupedDroplist : Command
{
    public override void Execute(CommandContext context)
    {
        ID id = ID.Null;

        Item item = context.Items[0];

        var targetName = WebUtil.GetFormValue(context.Parameters["fieldId"]);

        if (item != null && !string.IsNullOrEmpty(targetName))
        {
            foreach (Field field in item.Fields.Where(Utility.IsGroupedDroplistField))
            {
                if (field.HasValue && field.Value.Equals(targetName) && !string.IsNullOrEmpty(field.Source))
                {
                    var grandChildren = new List<Item>();

                    Item sourceItem = item.Database.GetItem(field.Source);

                    if (sourceItem != null)
                    {
                        grandChildren = (from c in sourceItem.Children
                            select c.GetChildren()).SelectMany(g => g).ToList();
                    }
                    else
                    {
                        List<Item> children = Utility.GetItemsFromQuery(field.Source, item).ToList();

                        grandChildren = (from c in children
                                            select c.GetChildren()).SelectMany(g => g).ToList();
                    }

                    Item targetItem = grandChildren.FirstOrDefault(c => c.Name == targetName);

                    if (targetItem != null)
                    {
                        id = targetItem.ID;
                        break;
                    }
                }
            }
        }

        Sitecore.Context.ClientPage.SendMessage(this, "item:load(id=" + (id != ID.Null ? id.ToString() : string.Empty) + ")");
    }
}