Question

I m trying to implement my own version of NSViewController (for backwards compatibility), and I ve hit a problem with bindings: Since bindings retain their target, I have a retain circle whenever I bind through File s owner.

So I thought I d just explicitly remove my view from its superview and release the top level objects, and that would take care of the bindings, because my controller isn t holding on to the views anymore, so they release me and I can go away. But for some reason, my view controller still doesn t get released. Here s a sample app exhibiting the problem:

http://dl.dropbox.com/u/34351/BindingsLeak.zip

Build it, launch it, and hit Cmd-K ("Create Nib" in "Edit" menu) to load a NIB into the empty window. Hit Cmd-K again to release the first view controller (TestNibOwner) and load a new one. The old view controller never gets dealloced, though.

Remove the "value" binding on the checkbox, and it gets released just fine.

If you set breakpoints at the release/retain/autorelease overrides, you see that _NSBindingInfo retains the TestNibOwner, but never releases it in the leaking case.

Anyone know how to fix this?

Answer 1

One thing I ve done for the same problem is to create a proxy NSObjectController inside my nib. My NSViewController-like class has a pointer to this proxy and all bindings are bound through it. When I want to cleanup the view controller, I then do [selfProxy setContent:nil] on the object controller and release the view controller. In this instance the NSObjectController proxy acts as the auto-unbinder in this case.

It s more manual and you can t just release the view by itself, but it does solve the retain problem.

I d suggest you do this:

-(void) releaseTopLevelObjects
{
    // Unbind the object controller s content by setting it to nil.
    [selfProxy setContent:nil];

    NSLog( @"topLevelObjects = %@", topLevelObjects );
    [topLevelObjects release];
    topLevelObjects = nil;
}

In your nib, bindings would happen through a path like:

selfProxy.content.representedObject.fooValue

Answer 2

Doing a little investigation with class-dump and friends, it looks like Apple has a private class called NSAutounbinder that takes care of this dirty work for classes such as NSViewController and NSWindowController. Can t really tell how it works or how to replicate it though.

So, I can t really answer your question on how to prevent the retain cycle from happening for arbitrary bindings in a loaded nib, but perhaps it s some consolation to know that Apple is cheating, and you re not missing anything obvious. :-)

Answer 3

When you remove your view from its superview, are you also sending it another -release message? It was created by unarchiving from the nib, right?

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