Determines permitted mime types from the Secure File Upload Field

DeterminePermitedMimeTypes.cs

private List<FileType> DeterminePermitedMimeTypes()
{
    var fileTypes = new List<FileType>();

    if (FieldItem != null)
    {
        var itemIds = new List<string>();

        var regexSelectedValue = new Regex(@"<selectedvalue>(.*?)</selectedvalue>".ToLower());
        var selectedValueNodes = regexSelectedValue.Matches(FieldItem["Parameters"].ToLower());

        if (selectedValueNodes.Count > 0)
        {
            foreach (Match selectedValueNode in selectedValueNodes)
            {
                var regexItems = new Regex(@"<item>(.*?)</item>".ToLower());
                var itemNodes = regexItems.Matches(selectedValueNode.ToString());

                itemIds.AddRange(from Match itemNode in itemNodes
                                    where itemNode.Groups[1] != null 
                                    && !string.IsNullOrEmpty(itemNode.Groups[1].Value) 
                                    && TryParseGuid(itemNode.Groups[1].Value)
                                    select itemNode.Groups[1].Value);
            }

            if (itemIds.Any())
            {
                var fileTypeItems = itemIds.Select(i => Sitecore.Context.Database.GetItem(i));
                fileTypes = fileTypeItems.Select(i => new FileType(i)).ToList();
            }
        }
    }

    return fileTypes;
}