Bill,
On Mar 2, 2008, at 5:35 PM, Ben Trumbull wrote:
My question is, why would changing a property value cause another
property to have its retain count increase?
No idea. Why don't you run it in gdb and break on the -retain
method and get some stack traces ?
This works best if the class you're debugging (in this case the
value window controller) has a custom retain/release method that you
can break on instead of NSObject's etc. If it doesn't, you can
trivially make one by adding a category on it and putting -retain/-
release/-autorelease methods on it that simply call super.
Good idea. Here's the stack trace:
#0 0x000029aa in -[NSWindowController(MainWindow) retain] at
MainWindowController.m:35
#1 0x92dfa378 in -[NSManagedObject(_NSInternalMethods)
_newPropertiesForRetainedTypes:andCopiedTypes:preserveFaults:]
#2 0x92dfa250 in -[NSManagedObject(_NSInternalMethods) _allProperties]
#3 0x92dfa185 in -[NSManagedObjectContext(_NSInternalChangeProcessing)
_establishEventSnapshotsForObject:]
#4 0x92dfd516 in _PFFastMOCObjectWillChange
#5 0x92dfb4e3 in -[NSManagedObject willChangeValueForKey:]
#6 0x00021a6c in -[Window setOpenAtLaunch:] at Window.m:117
Not sure what to make of it, nor why setting the property openAtLaunch
increments the retain count for the window controller property.
At a low level, what's going on is that you're dirtying a managed
object and Core Data is taking a snapshot of the previous state for
this user event. The snapshot supports undo, rollback, and the merge
policies, among other odds and ends. This snapshot may be pushed
onto the undo stack, or simply kept around until you -save:,
-rollback, or -reset the NSManagedObjectContext
At a high level, you've created a retain cycle between the M & V
layers of the MVC pattern.
After some thought, it seems a bit weird to make the
NSWindowController an attribute of a managed object. Technically,
you could solve this problem by making it an unmodeled property
(ivar). However, this is probably a symptom of a larger design issue.
--
-Ben
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