Question

I am trying to execute this function:

public static int QueryInterface(
    IntPtr pUnk,
    ref Guid iid,
    out IntPtr ppv
)

where

pUnk
Type: System.IntPtr
The interface to be queried.

Basically, Marshal.QueryInterface requests a pointer to a specified interface from a COM object. There is a number of interfaces I would like to query (all from IPersist), so how do I go about obtaining a reference pointer to these interfaces?

Note: IPersistStorage is one of them.

edit (this works):

// Use the CLSID to instantiate the COM object using interop.
Type type = Type.GetTypeFromCLSID(myGuid);
Object comObj = Activator.CreateInstance(type);

// Return a pointer to the objects IUnknown interface.
IntPtr pIUnk = Marshal.GetIUnknownForObject(comObj);
IntPtr pInterface;
Int32 result = Marshal.QueryInterface(pIUnk, ref myGuid, out pInterface);

Answer 1

Read the last line of the remarks section on the Marshal.QueryInterface() page.

The QueryInterface method exposes the IUnknown::QueryInterface method of a COM object, which attempts to obtain a specific interface pointer. […] To obtain an IntPtr value that represents a IUnknown interface pointer, you can call Marshal.GetComInterfaceForObject, Marshal.GetIUnknownForObject, or Marshal.GetIDispatchForObject.

I believe you’re looking for the Marshal.GetComInterfaceForObject() method.