How can I obtain the list of files in a project from VSIX(/MPF) code?

I am building a VSIX package to support a custom language in Visual Studio using MPF. I am in a custom designer and I need to find the files referenced in the project to resolve some dependencies. Where can I access this list?

I assume, that you´re using MPF to implement the project system for your custom language service. When doing so, you probably have a project root node which is derived from either ProjectNode or HierarchyNode...

If so, you could share the root node´s instance with the designer and try to find files by traversing the hierarchy, for instance...

internal class HierarchyVisitor
{
    private readonly Func<HierarchyNode, bool> filterCallback;

    public HierarchyVisitor(
        Func<HierarchyNode, bool> filter)
    {
        this.filterCallback = filter;
    }

    public IEnumerable<HierarchyNode> Visit(
        HierarchyNode node)
    {
        var stack = new Stack<HierarchyNode>();
        stack.Push(node);
        while (stack.Any())
        {
            HierarchyNode next = stack.Pop();
            if (this.filterCallback(next))
            {
                yield return next;
            }

            for (
                HierarchyNode child = next.FirstChild; 
                child != null; 
                child = child.NextSibling)
            {
                stack.Push(child);
            }
        }
    }
}

To get a list of all nodes in the hierarchy, you could just do...

ProjectNode root = ...
var visitor = new HierarchyVisitor(x => true);
IEnumerable<HierarchyNode> flatList = visitor.Visit(root);

Or to filter for a certain file type, you could try something like this...

ProjectNode root = ...
var visitor = new HierarchyVisitor((HierarchyNode x) => 
    {
        const string XmlFileExtension = ".xml";
        string path = new Uri(x.Url, UriKind.Absolut).LocalPath;
        return string.Compare(
            XmlFileExtension, 
            Path.GetFileExtension(path), 
            StringComparison.InvariantCultureIgnoreCase) == 0;
    });

IEnumerable<HierarchyNode> xmlFiles = visitor.Visit(root);