Re: Outlets / IBOutlet declarations (was Re: Interface Builder & Wiring Objects)
Re: Outlets / IBOutlet declarations (was Re: Interface Builder & Wiring Objects)
- Subject: Re: Outlets / IBOutlet declarations (was Re: Interface Builder & Wiring Objects)
- From: Brian Stern <email@hidden>
- Date: Tue, 18 Nov 2008 01:14:03 -0500
On Nov 18, 2008, at 12:59 AM, Roland King wrote:
Hey Brian -
Outlets for iPhone OS are established by calling
setValue:forKeyPath:. The behavior of setValue:forKeyPath: is
that if a setter exists, it is called. If a setter does not
exist, the instance variable is looked up and set directly, and
if it is an object, it is retained. This means that for
IBOutlets, with no setters, they're retained in iPhone OS. This
is different from Mac OS X. If you're writing code on both
platforms, or are planning to, you should always use properties
on both platforms since it makes the decision to retain outlets
explicit and obvious.
How come the documentation that mmalc quoted doesn't have this
clear statement?
which one did he quote, the one I suggested to you has it .. it's
under Nib Object Retention. It's a page I have bookmarked because as
I switch between iPhone and regular OSX I like to remind myself what
it says. It's pasted below.
Yes, that's it. I've read it plenty of times.
iPhone OS - managed memory model
Objects in the nib file are created with a retain count of 1 and
then autoreleased. As it rebuilds the object hierarchy, however,
UIKit reestablishes connections between the objects using the |
setValue:forKey:| method, which uses the available setter method or
retains the object by default if no setter method is available.
I admit that I didn't internalize this statement because the behavior
is different from the Mac. I also didn't internalize this because it
seems to contradict the standard Cocoa memory management rules. My
code doesn't retain the outlets so it shouldn't have to release them.
If you define outlets for nib-file objects, you should also define a
setter method for accessing that outlet.
Why SHOULD?
Setter methods for outlets should
Why SHOULD?
retain their values, and setter methods for outlets containing top-
level objects must retain their values to prevent them from being
deallocated. If you do not store the top-level objects in outlets,
you must retain either the array returned by the |
loadNibNamed:owner:options:| method or the objects inside the array
to prevent those objects from being released prematurely.
In a nib loaded by UIViewController I have no access to the top level
objects array so this isn't usually relevant.
The shoulds in there confused me. The fact that the behavior is
different from the Mac confused me. The fact that the behavior seems
contrary to standard Cocoa memory management rules confused me. I
assure you that I'm not the only person confused by this and who
doesn't understand this.
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