Populate a EPiServer CMS 7 drop down list in dynamic content from AppSettings

PropertyAppSettingsDropDownList.cs

using EPiServer.Core;
using EPiServer.PlugIn;
using EPiServer.SpecializedProperties;
using EPiServer.Web.PropertyControls;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Web.UI.WebControls;
 
namespace Namespace.Path.In.Project
{
    /*
    Init using: new PropertyAppSettingsDropDownList { AppSetting = "AppSettingsValue" }
    */
  
    [PropertyDefinitionTypePlugIn(DisplayName = "Dropdown list populated from AppSettings")]
    public class PropertyAppSettingsDropDownList : PropertyDropDownList
    {
        public string AppSetting { get; set; }
 
        public override IPropertyControl CreatePropertyControl()
        {
            if (string.IsNullOrEmpty(AppSetting))
            {
                throw new Exception("AppSetting missing.");
            }
 
            return new AppSettingsDropDownControl { AppSetting = AppSetting };
        }
    }
 
    public class AppSettingsDropDownControl : PropertyDropDownListControl
    {
        public string AppSetting { get; set; }
 
        public PropertyDropDownList DropDownListValue
        {
            get { return PropertyData as PropertyDropDownList; }
        }
 
        protected override void SetupEditControls()
        {
            Setup();
        }
 
        protected virtual void Setup()
        {
            var selectedValue = string.Empty;
 
            if (DropDownListValue != null && DropDownListValue.Value != null)
            {
                selectedValue = (string)DropDownListValue.Value;
            }
 
            AddListItems(selectedValue);
            EditControl.DataBind();
        }
 
        protected virtual void AddListItems(string selectedValue = null)
        {
            var appSettings = ParseAppSettings();
 
            foreach (var item in appSettings)
            {
                if (item.Value == selectedValue)
                {
                    item.Selected = true;
                }
 
                EditControl.Items.Add(item);
            }
        }
 
        protected IEnumerable ParseAppSettings()
        {
            var setting = ConfigurationManager.AppSettings[AppSetting];
            var list = new List();
 
            foreach (var item in setting.Split('|'))
            {
                var itemSplit = item.Split(';');
                var itemName = itemSplit[0];
                var itemId = itemSplit[1];
                var returnItem = new ListItem(itemName, itemId);
 
                list.Add(returnItem);
            }
 
            return list;
        }
    }
}