Creating a custom datatype in Umbraco

I am trying to create a custom datatype. The intention being a dropdown list. As of right now, I can access the control I created but no properties or values are showing up within it. Just the blank drop down.

public partial class usercontrols_admin_customDataType_CountryDropDown : 
    System.Web.UI.UserControl,
    umbraco.editorControls.userControlGrapper.IUsercontrolDataEditor
{
    public string umbracoValue;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
        {
            DataSet ds = new DataSet();

            FormFieldBuilder countries = new FormFieldBuilder();
            ds = countries.GetAllCountries();

            ddCountries.DataSource = ds;
            ddCountries.DataTextField = ds.Tables[0].Columns["DisplayName"].ToString();
          开发者_开发技巧  ddCountries.DataValueField = ds.Tables[0].Columns["guiCountryID"].ToString();
            ddCountries.DataBind();
        }
    }

    #region IUsercontrolDataEditor Members

    public object value
    {
        get
        {
            return ddCountries.SelectedValue;
        }
        set
        {
            if (value != null) 
            {
                ddCountries.SelectedValue = value.ToString();
            }
        }
    }

    #endregion
}

This line:

if (Page.IsPostBack)

Should be:

if (!Page.IsPostBack)

Otherwise the drop down will not be populated until after the form has been submitted (posted back)

download UComponent add-on & upload it to package. there you may create you own customized Data types with the help of this addon ,there no need to code.