Programmatically adding options to EPi CMS 6 R2 drop-down list property when using PageTypeBuilder 2.0

Since EPi CMS had property types with custom settings added I have found the drop-down list (EPiServer.SpecializedProperties.PropertyDropDownList) especially useful for allowing an editor to choose from a few different teaser content block appearances when creating teaser page types. The out-of-the-box approach is for an CmsAdmin or developer to manually add key-value pair type options in the CMS admin mode for the property but when using PageTypeBuilder there is a nice way of adding settings programmatically:

I implemented it in a way so that I can add a drop-down list using the attribute class PropertyDropDownListSettings like this:

[PageTypeProperty(
    EditCaption = "Layout",
    DefaultValue = "default",
    Required = true,
    SortOrder = 11,
    Type = typeof(EPiServer.SpecializedProperties.PropertyDropDownList))]
[PropertyDropDownListSettings(
    Settings = new string[]
    {
        "Default|default",
        "Compact|compact",
        "Video|video",
        "RSS Feed|rss",
        "Wide|wide"
    })]
public virtual string TeaserLayout { get; set; }

Attribute classes only accept primitive constants and arrays of primitives as parameters and I wanted to add one to many name-value pairs of <string, string>. I settled for a string array with pipe separated pairs and some old fashioned string handling in the UpdateSettings method. I only tested this lightly so the following may be subject to update:

using System;
using System.Text;
using EPiServer.Web.PropertyControls.PropertySettings;
using PageTypeBuilder;

public class PropertyDropDownListSettingsAttribute : Attribute, IUpdatePropertySettings<MultipleOptionsListSettings>
{
    //// { "Name|value", "Name|value2", "Name|value3" }
    public virtual string[] Settings { get; set; }

    public bool OverWriteExistingSettings
    {
        get
        {
            return true;
        }
    }

    public int GetSettingsHashCode(MultipleOptionsListSettings settings)
    {
        StringBuilder sb = new StringBuilder();

        foreach (string optionValue in settings.ListOptions.Values)
        {
            sb.Append(optionValue);
        }

        return sb.GetHashCode();
    }

    public void UpdateSettings(MultipleOptionsListSettings settings)
    {
        if (this.Settings != null)
        {
            foreach (string pair in this.Settings)
            {
                string[] splitPair = pair.Split('|');

                if (splitPair.Length >= 2 &&
                    !string.IsNullOrEmpty(splitPair[0]) &&
                    !string.IsNullOrEmpty(splitPair[1]))
                {
                    if (settings.ListOptions.ContainsKey(splitPair[0]))
                    {
                        settings.ListOptions[splitPair[0]] = splitPair[1];
                    }
                    else
                    {
                        settings.ListOptions.Add(splitPair[0], splitPair[1]);
                    }
                }
            }
        }
    }
}

As you can tell, this allows for adding new name-value pairs and updating values for existing names. It's still possible to add additional values in admin mode since UpdateSettings will not remove anything. If a name-value pair is removed in the page type definition class file, then that value must be deleted in admin mode since it will remain active until someone does so.