I believe you mean

contentItem.Key

?

Because IPublishedContent has no method GetKey()

Yeah sorry I’m on my mobile. That should be the one.

Since you specifically mention IPublishedContent, and not IPublishedElement, Paul's example is unfortunately not entirely correct (sorry Poul 😉), as it doesn't account for the underlying type of the IPublishedContent (eg. whether it's content, media etc.).

The GetKey() method existed prior to Umbraco 9 (I can't remember if it even existed in Umbraco 8). As you found out, it should be the Key property instead.

Anyways, an IPublishedContent exposes an itemType property indicating the underlying type - so to get the UDI, I would create a method like:

public Udi GetUdi(IPublishedContent content) {
    if (content == null) throw new ArgumentNullException(nameof(content));
    return content.ItemType switch {
        PublishedItemType.Content => Udi.Create("document", content.Key),
        PublishedItemType.Media => Udi.Create("media", content.Key),
        PublishedItemType.Member => Udi.Create("member", content.Key),
        PublishedItemType.Element => Udi.Create("element", content.Key),
        _ => throw new InvalidOperationException($"Unsupported item type: {content.ItemType}")
    };
}

This checks against all current item types - except Unknown.

If you put it in a static class, you can even implement it as an extension method:

public static Udi GetUdi(this IPublishedContent content) {
    if (content == null) throw new ArgumentNullException(nameof(content));
    return content.ItemType switch {
        PublishedItemType.Content => Udi.Create("document", content.Key),
        PublishedItemType.Media => Udi.Create("media", content.Key),
        PublishedItemType.Member => Udi.Create("member", content.Key),
        PublishedItemType.Element => Udi.Create("element", content.Key),
        _ => throw new InvalidOperationException($"Unsupported item type: {content.ItemType}")
    };
}

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