Questions about releasing your DirectX interfaces

[chronozphere]

Hi everyone.

I was wondering...

Is there a dirrerence between doing this:

[pascal]
MyDirect3DInterface := nil;

//OR

MyDirect3dInterface.Release;
[/pascal]

and this:

[pascal]
if MyDirect3dInterface <> nil then MyDirect3dInterface.Release;

//OR

if MyDirect3dInterface <> nil then MyDirect3dInterface := nil;
[/pascal]

Until now, i usually set my interfaces to NIL to free them without the IF THEN check. However i often see this in other D3D sources (both pascal and C++).
So, Is there any difference between these methods.

I recall that i read somewere that releasing a method twice is bad:

[pascal]
MyDirect3dInterface.Release;
MyDirect3dInterface.Release;
[/pascal]

Is this also true when i do this??

[pascal]
MyDirect3dInterface := nil;
MyDirect3dInterface := nil;
[/pascal]

Can someone tell me what the right way is, because it's confusing me a bit.

Thanx alot

[Robert Kosek]

Yes, there is a difference!!

If you do this:
[pascal]MyInterface.Release;
assert(MyInterface = nil);[/pascal]
The assert will always be called. The same goes for Free. This doesn't mean you shouldn't destroy the object, but just that the variable remains active though the item is gone.

You should always call:[pascal]if MyInterface <> nil then begin
MyInterface.Release;
MyInterface := nil;
end;[/pascal]If you intend to check something based on the nil status.

[technomage]

If I remember my COM correctly

[pascal]
MyDirect3DInterface := nil;
[/pascal]

calls .Release in the background providing the interface supports IInterface (which all DirectX stuff does). I have never called .Release manually.

[Robert Kosek]

Ah; I have never worked with Interfaces directly so I wouldn't know. I just know I hit the paradigm with a component I'm working on, that freed things aren't nil. Most things in pascal are cross-applicable but I guess this isn't one.

[chronozphere]

So you mean calling "MyDirect3dInterface := nil" is enough?? :razz:

[savage]

So you mean calling "MyDirect3dInterface := nil" is enough?? :razz:

Because COM is reference counted, calling := nil should be enough.
There are instances where you may need to call _release and other stuff, but that would tend to indicate that you are doing more advanced stuff. If you are just doing normal vanilla DirectX stuff, setting the interface to nil should be fine. Otherwise do a search for "Delphi COM reference counting."