I was using my codeplex project ManagedMenuExtensions recently when I realized that it threw an Exception, when clicking on a menu attached to a C# project under a solution folder. The reason was that the object which normally contained an EnvDTE.Project when a project was clicked contained null, when this project was contained in a solution folder.

I normally use this code to get at the selected project (m_VSStudio is the DTE object of the current solution):

private UIHierarchyItem SelectedItem
{
  get
  {
    UIHierarchy uiHierarchy = m_VSStudio.ToolWindows.SolutionExplorer;
    if(uiHierarchy == null)
      return null;

    object[] items = uiHierarchy.SelectedItems as object[];
    if(items == null || items.Length == 0)
      return null;

    return items[0] as UIHierarchyItem;
  }
}

The SelectedItem.Object of type object now contains a EnvDTE.Solution object if the solution is selected in the solution explorer, and guess what :O) it contains an EnvDTE.Project if a project is selected. It is this SelectedItem.Object that contains null, if the project is contained in a solution folder.

I googled this problem and found others who had the same problem, but none with a solution, so I had to come up with my own. I don't know if this behaviour is by design from Microsoft, or if it is a bug.

My Solution

Normally I would test if a project is selected with this code:

var project = SelectedItem.Object as Project;
if (project != null)
{
    //Do something with the project
}

Now I use this code instead:

Project project = GetProject(SelectedItem.Object);
if (project != null)
{
    //Do something with the project
}

Where I implemented GetProject(...) as:

private Project GetProject(object selectedItemObject)
{
    var project = selectedItemObject as Project;
    if (project != null)
        return project; 

    var item = selectedItemObject as ProjectItem;
    if (item == null)
        return null; 

    return item.SubProject;
}

Not exactly beautiful, but that is to be expected when playing with Visual Studios AddIn model, and the kind of thing I try to hide in ManagedMenuExtensions. I haven't had a chance to look at Visual Studio 2010 yet, one could hope that they have done a better job of hiding the ugly underlying COM stuff.

Anyway, I hope this helps the next person who tries to search for a workaround for this rather weird behaviour.