Correct memory management in -awakeAfterUsingCoder: ?
Correct memory management in -awakeAfterUsingCoder: ?
- Subject: Correct memory management in -awakeAfterUsingCoder: ?
- From: Graham Cox <email@hidden>
- Date: Tue, 5 May 2009 14:45:18 +1000
I am trying to track down an over-release bug.
It looks like I'm doing something wrong in -awakeAfterUsingCoder:
which leads to an object being insufficiently retained.
I have two objects, A and B. A loads B from an archive within -
initWithCoder: while dearchiving and retains it. When B is dearchived,
it can be replaced by another object by its -awakeAfterUsingCoder:
method. If I detect that B should be replaced, I release the current B
as per the documentation and return the replacement without doing
anything regarding retain or release on it, as it's already retained
by the code that supplied it.
Subsequently it is this object that is over-released.
If I retain the object before returning it in -awakeAfterUsingCoder:,
the problem goes away, but this appears to violate normal memory
management rules, so it's not clear that this is the correct solution.
The documentation doesn't explicitly say anything about this either.
Rough outline of the code:
// in object A:
- (id) initWithCoder:(NSCoder*) coder
{
ivarB = [[coder decodeObjectForKey:@"B"] retain];
}
// in object B:
- (id) awakeAfterusingCoder:(NSCoder*) coder
{
id replacement = [someStorageLibrary objectSimilarTo:self]; //
<someStorageLibrary> is retaining <replacement>
if( replacement )
{
[self release]; // immediate release as per documentation
return replacement; //<--- to retain or to not retain, that
is the question...
}
else
{
[someStorageLibrary addObject:self];
return self;
}
}
tia,
--Graham
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