Hi all. I'm just getting into my first garbage collected Cocoa
project, and I'm a bit mystified by the behavior I'm seeing. I'm just
trying to make a custom about panel. I put this method in my
application delegate:
- (IBAction)orderFrontAboutPanel:(id)sender
{
if (!aboutController)
aboutController = [[AKAboutPanelController alloc]
initWithWindowNibName:@"AKSplash"];
[aboutController showWindow:nil];
}
I put this declaration of aboutController in my app delegate header:
__weak AKAboutPanelController *aboutController;
And then I implemented AKAboutPanelController like so:
@interface AKAboutPanelController : NSWindowController
{
}
@end
@implementation AKAboutPanelController
- (void)finalize
{
NSLog(@"AKAboutPanelController finalize");
[super finalize];
}
@end
My idea — perhaps being too clever for my own good — was that as
long as the about window was open, the window would be referenced by
the window list, and so the window and its controller would stick
around. Choosing the "About" menu item a second time would therefore
just call showWindow: on the controller again, ordering the window to
the front if it had gotten buried. As soon as the window was closed,
I figured it and its controller would be garbage collected, and the
weak reference to it in the app delegate would zero out, so then
choosing "About" would create a new controller and reload the nib.
But this is not what happened.
Instead, the about window sticks around for as long as it is the
key window (presumably the window is strong-referenced by AppKit or
somebody at a lower level than the Kit). As soon as it is not the key
window (click on a different window in the app) it gets garbage
collected immediately, even though it is still open! Now maybe this
is intended behavior, but it sure isn't what I expected; it seemed
intuitive to me that an open window, visible to the user, would not be
garbage collected. Is there a reason that the window list uses weak
references for visible windows?
So. I can think of any number of ways to fix this, of course, but
they all seem a little bit gross since they involve either tweaking
the garbage collector (CFRetain, for example) or making the reference
to the window controller in the app delegate strong, in which it
doesn't automatically zero and I have to set up a way for the
windowcontroller to tell the app delegate that it's no longer needed.
There must be a better pattern; I imagine I'm just not used to
thinking in garbage-collection terms yet. So what's the right way to
do this?
Thanks...
Ben Haller
Stick Software
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