Orchard alternates based on Tag - orchardcms

Question

I want to create alternates for content item based on its tag value.
For example, I want to create an alternate called List-ProjectionPage-tags-special
Searching the nets directs me to implement a new ShapeDisplayEvents
Thus, I have
public class TagAlternatesFactory : ShapeDisplayEvents
{
public TagAlternatesFactory()
{
}
public override void Displaying(ShapeDisplayingContext context)
{
}
}
In the Displaying method, I believe I need to check the contentItem off the context.Shape and create an alternate name based off of that (assuming it has the TagsPart added to the content item).
However, what do I do with it then? How do I add the name of the alternate? And is that all that's needed to create a new alternate type? Will orchard know to look for List-ProjectionPage-tags-special?

Answer 1

I took a cue from Bertrand's comment and looked at some Orchard source for direction.
Here's my implementation:
public class TagAlternatesFactory : ShapeDisplayEvents
{
public override void Displaying(ShapeDisplayingContext context)
{
context.ShapeMetadata.OnDisplaying(displayedContext =>
{
var contentItem = displayedContext.Shape.ContentItem;
var contentType = contentItem.ContentType;
var parts = contentItem.Parts as IEnumerable<ContentPart>;
if (parts == null) return;
var tagsPart = parts.FirstOrDefault(part => part is TagsPart) as TagsPart;
if (tagsPart == null) return;
foreach (var tag in tagsPart.CurrentTags)
{
displayedContext.ShapeMetadata.Alternates.Add(
String.Format("{0}__{1}__{2}__{3}",
displayedContext.ShapeMetadata.Type, (string)contentType, "tag", tag.TagName)); //See update
}
});
}
}
This allows an alternate view based on a tag value. So, if you have a project page that you want to apply a specific style to, you can simply create your alternate view with the name ProjectionPage_tag_special and anytime you want a projection page to use it, just add the special tag to it.
Update
I added the displayedContext.ShapeMetadata.Type to the alternate name so specific shapes could be overridden (like the List-ProjectionPage)