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DirectShow Interface releasing

Posted on 2004-04-25
2
Medium Priority
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Last Modified: 2012-08-13
Hi.

I have a probblem releasing the DirectShow Interfaces previously allocated. Example:

var
  gb: IGraphBuilder;
  mc: IMediaControl;

...
CoCreateInstance(CLSID_FilterGraph, nil, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, gb);
gb.QueryInterface(IID_IMediaControl, mc);
...
if(mc<>nil) then
begin
  mc._Release;
  mc:=nil;
end;
if(gb<>nil) then
begin
  gb._Release;
  gb:=nil;
end;

I always receive a Access violation. Do you know what may be causing this?

PS:
I'm using the DirectShow header from www.progdigy.com.
Thanks.
0
Comment
Question by:BlueAlien
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2 Comments
 
LVL 26

Accepted Solution

by:
Russell Libby earned 500 total points
ID: 10913471

Delphi's interface pointers are considered smart pointers, meaning this: versions since Delphi3 provide automatic management of interface variables, so calling

mc:=nil;

will handle calling the interface Release for you, thus you should *never* (almost never) call Release yourself. As well, if the variable is local in scope, the interface will be released for you at the end of the function/procedure if the variable is non nil. So, as a general rule of thumb, you will almost never need to call AddRef/Release on interface pointers. (The only exceptions would be in rare cases where the interface is cast and held as a generic pointer type.)

Regards,
Russell
0
 

Author Comment

by:BlueAlien
ID: 10917518
Thanks.
0

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