I have a form that I use to show some information for some seconds. Is it ok for the form to free itself? Can I start a timer in the constructor, and then call self.free in the timer-event? Or will this potentially lead to trouble?
A:
I have a whole suite of objects that free themselves, and I've run various tests on them with no problems/leaks shown. A TForm might be more complex, but as long as Self.Free() is the last call made, you ought to be safe.
(For those wondering why on earth I have object that free themselves; I pass them around the system a lot, so I implemented by own reference counting scheme. When the last reference is released, so the object frees itself).
Drarok
2009-04-02 08:54:08
But Self.Free would almost *never* be the last call made by a form because a form is almost always running code in reaction to some user action. Use Release instead.
Rob Kennedy
2009-04-02 13:25:49
Why not just use Interfaces for reference-counting?
Mason Wheeler
2009-04-02 15:58:07
I'm not after reference-counting. I'm after a form that you create one place, and then frees its self when it wants to.
Vegar
2009-04-02 20:26:47
@Vegar: I think Mason's comment was meant for Drarok who implemented his own reference counting and not for you :)
Smasher
2009-04-03 10:21:42
Hehe. Yes, that makes sense. For some reason, I think everythings about me...
Vegar
2009-04-03 20:03:51
+9
A:
You can make the form to free itself when it gets closed by the user or from code:
procedure TForm27.FormClose(Sender: TObject; var Action: TCloseAction);
begin
Action := caFree;
end;
procedure TForm27.FormCreate(Sender: TObject);
begin
Timer1.Enabled := True;
end;
procedure TForm27.Timer1Timer(Sender: TObject);
begin
Timer1.Enabled := False;
Close;
end;
Make sure you supply an owner in the constructor incase the application shutdowns and the form is not destroyed at the time. The owner will free the form before freeing itself.
pani
2009-04-02 09:03:28
The more I think about it, the more I like the TCloseAction-idea. Maybe I should use that instead of release...
Vegar
2009-04-02 20:32:34
+20
A:
In addition, with a form you can call release.
It sends a CM_RELEASE message to the form. As a reaction it calls Free. The advantage of release is that there are no messages left for the form which could result in a crash.
Gamecat
2009-04-02 09:16:24
Yes, but you should remember that Delphi's TComponent overrides the interface's reference counting, which often causes confusion.
Fabio Gomes
2009-04-02 12:26:44
Using interfaces, the form would be freed when it goes out of scoop. I don't want that. I want it to live as long as it wants without any references to it, and then free it self when its done showing it self.
Vegar
2009-04-02 20:29:04
Fabio: I'm sure you could override that.Vegar: Interfaces are reference counted, not scope-managed.
Arafangion
2009-04-02 22:39:10
Yes, but as long as you don't keep a reference, wouldn't the referencecount go to zero when the code where you created the form goes out of scope?
Vegar
2009-04-03 08:38:06
Only if you never pass it to something else... When you create the object, the ref gets incremented, so it is 1. When you assign it to something else, it becomes incremented again, so it is 2. When it leaves scope, it gets decremented, to ONE, and thus isn't destroyed.
Arafangion
2009-04-04 04:30:35