TagList/UserDefinedTagsPart on SlideLayoutPart

Hi, how would I add a taglist to a layoutslide?

I got the following code, but it doesn't work:

private int i = 0;

private void Button_Click(object sender, RoutedEventArgs e)
{
PresentationDocument presentationDocument = PresentationDocument.Open(@"D:\Merge\PresentationTemplate.pptx", true);
PresentationPart presentationPart = presentationDocument.PresentationPart;

foreach (var slideLayoutPart in presentationPart.SlideMasterParts.First().SlideLayoutParts)
{
UserDefinedTagsPart userDefinedTagsPart1 = slideLayoutPart.AddNewPart();
TagList tagList1 = new TagList();
Tag tag1 = new Tag() { Name = "layoutName", Val = "mslide" + ++i };
tagList1.Append(tag1);
userDefinedTagsPart1.TagList = tagList1;

}

//presentationPart.SlideMasterParts.First().SlideMaster.Save();

OpenXmlValidator validator = new OpenXmlValidator();
var errors = validator.Validate(presentationDocument);

presentationPart.Presentation.Save();
MessageBox.Show("Done");
}

Sorry but I'm unable to test this scenario right now but I would suggest trying to strongly type where you add your new UserDefinedTagsPart.

Instead of:
UserDefinedTagsPart userDefinedTagsPart1 = slideLayoutPart.AddNewPart();

Try this:
UserDefinedTagsPart userDefinedTagsPart1 = slideLayoutPart.AddNewPart<UserDefinedTagsPart>();

As I mentioned, I can test this scenario right now but give my suggestion a try and let me know if you have any issues and I can try it in my development environment.