Question about COM, WinInet and FTP
Enter callback interfaces and connection points. These are best described
in the literature, but the idea is simple - you call through an interface
which the caller passed to you prior to the asynchronous operation to
indicate its progress. The simpler (and more to the point) callback
approach will involve the client passing an interface pointer to the
callback object when initiating the async operation. The server object
AddRef-s the callback interface pointer and calls through it later. The
more generic connection points (less useful here, but much simpler in
a browser with scripts due to the ready support for connection points)
involvesthe object publishing its outgoing interface in the type library
and providing the appropriate interfaces: IConnectionPointContainer
and IConnectionPoint (on a separate object). ATL has ready support
for connection points too.
Check out these sources:
"Inside OLE" by Kraig Brosckschmidt, MSDN Library under \Books
"Beginning ATL3 COM Programming" By Dr Richard Grimes, Wrox Press
"Professional ATL COM Programming" By Dr Richard Grimes, Wrox Press
The first describes what Connectable Objects (AKA conection points)
really are. The other two describe the ATL support. (I think either will
do.) At any rate, any decent ATL book describes that...
--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
MVP VC FAQ: http://www.mvps.org/vcfaq
=====================================
Quote:
> Hi,
> I am after some clarification whether this is possible or not and if I
> am going about this the right way. What I want to do is get a "submit"
> button on a web page to take some some filename information from an
> HTML form and then FTP it to a specified server.
> I want to wrap all this up in COM using wininet. I have got as far as
> creating a the COM interface and implmenting a couple of methods to
> connect to the FTP server and actually managed to call FTPPutFile
> fine.
> I want to make the whole process better though...
> When control moves into the COM method the browser locks up (whilst
> the transfer is in progress) and only unfreezes when the transfer is
> finished. So I moved the FTPPutFile into another thread and everything
> works great. But I really want some sort of progress indicator on the
> client browser. I have been looking at the async communication and
> callbacks. Can this be used to do what I need? I know I could get the
> status of the transfer from the callback function at each stage and
> somehow return that to the browser to let the user know what's going
> on, but I'm a bit lost about how to do it. How can my COM object
> return this status to the browser? Surely I would have to call the
> method from the web page to get some status value from the object?
> I am also having problems getting the InternetSetStatusCallback
> function working!
> I am calling InternetOpen then using the handle returned by that
> method in the InternetSetStatusCallback call. This too succeeds but I
> don't think I am waiting correctly for the handle or something. To be
> honest I am having trouble debugging the COM methods so any help here
> would be much appreciated!! By the way, I am using ATL and VC++.
> thanks,
> Andy
