Question

I am working with ESRI’s ArcObjects COM Library, i am trying really hard to figure out what type “selected” should be:

IMxDocument doc = m_application.Document as IMxDocument;
object selected = doc.SelectedItem;

SelectedItem returns a comobject (Not Null), generally representing the data type that is currently selected. However i do not have the faintest idea what type i am supposed to cast it to. When i debug it, i don’t really see anything useful:

https://i.stack.imgur.com/gHlnA.jpg

(watch debug after the value is set)

ESRI’s ArcObjects library is huge, and is pretty poorly documented, i simply cannot figure it out. I even went so far as to manually check about 50 or so interfaces that i thought it should be.

Does anyone have any ideas how i can figure this out?

EDIT To clarify their documentation is absolutely no help, neither is their forums.

Answer 1

After reading your question, the answers, and the comments, you may have to write a utility to find the answer by brute force.

Use reflection to scrape a list of interfaces out of your interop assembly, then simply loop over this list and see if your object supports each interface in turn.

Update

Some sample code:

    object unknown = //your com object...

    Type someComObjectType = typeof(ExampleTypeInInteropAssembly);

    Assembly interopAssembly = someComObjectType.Assembly;

    Func<Type, bool> implementsInterface = iface =>
    {
        try
        {
            Marshal.GetComInterfaceForObject(unknown, iface);
            return true;
        }
        catch (InvalidCastException)
        {
            return false;
        }
    };

    List<Type> supportedInterfaces = interopAssembly.
        GetTypes().
        Where(t => t.IsInterface).
        Where(implementsInterface).
        ToList();

    if (supportedInterfaces.Count > 0)
    {
        supportedInterfaces.ForEach(Console.WriteLine);
    }
    else
    {
        Console.WriteLine("No supported interfaces found :(");
    }