🚀 go-pugleaf

"Enrique" <enridp@yahoo.com.ar> wrote in message
news:4588092d@newsgroups.borland.com...

> And yes, I need more practice with these interfaces, but in C++ it
> seems so complicated... we can see it just viewing the translation to
> C++ of the really simple code in Delphi... why it's so different?

Because the Delphi language has built-in support for interfaces, so it can
handle reference counting, QueryInterface(), and IDispatch::Invoke()
automatically.  The C++ language, however, does not natively have such rich
interface support, so you have to write extra code to manage it all
manually.

> MSDN design its interfaces thinking in Object Pascal?

No.  On the contrary, just about everything Microsoft does is actually
designed for C++ specifically.  What I showed you is similar code to what
VC++ programmers would have to use (just using Microsoft wrappers instead of
Borland wrappers).  It is just that Borland designed Delphi to work more
integrated with Microsoft technologies.  Delphi code may be cleaner, but the
runtime behavior is still the same either way.

> QueryInterface is like a typecasting?

An interface cannot safely be type-casted from one type to another directly.
QueryInterface() is the only safe way to get one interface type from
another, by actively asking the source interface if it supports a specific
type or not, and if so to then return such a pointer (with proper reference
counting, of course).

> In delhpi we can do this:

The "as" operator in Delphi is just a wrapper for QueryInterface().  If
QueryInterface() returns an error, the "as" operator throws an exception.

> IHTMLElement element;

You have to declare those interfaces as pointers:

    IHTMLElement *element;
    IHTMLElementCollection *childrenElements;

> childrenElements = (IHTMLElementCollection)element.children;

You cannot type-cast like that.  You must use QueryInterface() instead (and
"children" is not a VCL property, so you have to call the get_children()
method instead):

    IDispatch *disp;
    element->get_children(&disp);
    disp->QueryInterface(IID_IHTMLElementCollection,
(LPVOID*)&childrenElements);
    disp->Release();
    //...
    childrenElements->Release();

> childrenElements =
dynamic_cast<IHTMLElementCollection*>(element->children);

You cannot use dynamic_cast on an interface.


Gambit