Question

I’m currently working with the XMPP Library for Objective-C, and I’m using the “Desktop” example code.

It logs in fine; however, when I open a new chat, or someone sends me a message, it crashes.

This seems like where something goes wrong:

XMPPStream[11678:1b03] RECV: 
2012-06-05 15:03:59:379 XMPPStream[11678:1b03] RECV: 
2012-06-05 15:03:59:382 XMPPStream[11678:403] RosterController: xmppRosterDidChange:
2012-06-05 15:03:59:387 XMPPStream[11678:403] RosterController: xmppRosterDidChange:
2012-06-05 15:04:01:900 XMPPStream[11678:403] tableView:shouldEditTableColumn:"jid" row:0
2012-06-05 15:04:01:900 XMPPStream[11678:403] user: 
objc[11678]: cannot form weak reference to instance (0x7fcd4a498930) of class ChatController

and

objc[11998]: cannot form weak reference to instance (0x7f853bd17c70) of class ChatController
(lldb) 
(lldb)

What does “Cannot form weak reference to instance….of class ChatController” mean? Do you guys know how I can fix it? I used an older version of this code with Snow Leopard and it worked, Lion is screwing me up!

Thank you!

Answer 1

Looking at Mike Ash’s blog, I found an interesting paragraph:

ARC’s implementation of zeroing weak references requires close
coordination between the Objective-C reference counting system and the
zeroing weak reference system. This means that any class which
overrides retain and release can’t be the target of a zeroing weak
reference. While this is uncommon, some Cocoa classes, like NSWindow,
suffer from this limitation. Fortunately, if you hit one of these
cases, you will know it immediately, as your program will crash with a
message like this:

objc[2478]: cannot form weak reference to instance (0x10360f000) of class NSWindow

If you really must make a weak reference to classes such as these, you
can use the __unsafe_unretained qualifier in place of __weak.

Did you turn ARC on in your app? If you turn it off, do you get better results?