Is it possible to hooking COM interface function?

[GF-Huang]

If yes, can someone give an minimum example?

[m417z]

You can hook a COM interface function like any other function.
Example: https://github.com/ramensoftware/windhawk-mods/blob/a5f2753114108d8032a62ddb858864a7aa39e27a/mods/taskbar-start-button-position.wh.cpp#L534-L539

[GF-Huang]

OK, thank you!

[GF-Huang]

Is it get the hooking target function from vtable which take by winrt::get_abi necessary?

Is it possible do it like this (not sure is the statement correct):

WindhawkUtils::SetFunctionHook(&element->Arrange, hook, original);

Because I don't know the order of function in the vtable.

[m417z]

No, I don't think there's a way to achieve it without specifying the index. You should be able to see it in the COM object definition, usually by going to the method's definition in the editor.

[GF-Huang]

How about if I don't know the actual COM object, but only the interface? Such like ITfThreadMgr. Is it the index of function in vtable still determined by the method's definition in the editor?

You don't know the actual object definition, but only the interface:

HRESULT hr;
ITfThreadMgr* pThreadMgr;

hr = CoCreateInstance(CLSID_TF_ThreadMgr, 
                      NULL, 
                      CLSCTX_INPROC_SERVER, 
                      IID_ITfThreadMgr, 
                      (void**)&pThreadMgr);

[m417z]

You need both the index number, and an instance of the object to access the vtable.

If you don't have an instance of the object, you can either wait until you get one, or you can perhaps find the function using a different approach, such as debug symbols or byte patterns.