iphone debugging help- see when objects are released?

Question

I'm a little ways into developing my first iphone app, and I've been running into exc_bad_access a lot. (I'm sure it's because I'm not designing stuff in a very MVC-proper way yet.)

It's extremely frustrating trying to hunt down why I'm running into these errors all the time... is there a way in the xcode debugger to keep a watch list of pointers, so you can actually see when various objects are being released? Something, anything that can give me more of a visual understanding of why my program design is flawed?

In particular, I keep having trouble with my "webobject" class I've wrapped all of my NSURLConnection methods in. When I try to call performselector to the view controller that initiated a "webobject" request, I keep getting exc_bad_access when I try to access the webobject's synthesized properties. Is there something fundamentally wrong with my notion that I should wrap all of my webservice-related methods into a class that I can import anywhere?

Answer 1

Dave,

I don't know of a way to trace the deallocation of objects (especially native objects like NSStrings). But, I experienced a similar abundance of exc_bad_access messages when starting Objective-C programming. But one day I read something that helped me alot to get rid of these messages:

If you create an object using alloc, copy, or a method that begins with new, then it is your object to manage and dealloc. You can call retain and release and that cycle will work as expected on those objects. If you never call release or dealloc on it, it will hang around foreever and be a leak. If you call a method that is something like 'stringWithFormat', numberWithYadaYada then that object is set for autorelease. Meaning, as soon as you exit the method that is using it, it may get dealloced. Therefore, if you've called one of these autorelease methods, you must retain it if you want to see it later on.

I suspect that either your delegate or NSURLConnection is getting autoreleased, that is the cause of your bad access messages.

Jack

Answer 2

You could try creating a breakpoint on -[NSObject dealloc] (or the same method on the subclass you are targetting).

I would also refer you to one of the many Cocoa memory handling tutorials.

Answer 3

Just as a general thing, you should run as a static analyzer and it will probably tell you when you are over or under retaining objects.

pertinent stackoverflow question

Answer 4

I ended up reading up about NSZombieEnabled, which has helped me track down those exc_bad_access messages. More info here: http://www.cocoadev.com/index.pl?NSZombieEnabled