On May 29, 2011, at 12:20, Jerry Krinock wrote:
> - (id)initWithDocUuid:(NSString*)docUuid {
> NSManagedObjectContext* moc ;
> moc = [[BkmxBasis sharedBasis] exidsMocForIdentifier:docUuid] ;
>
> self = [super initWithManagedObjectContext:moc
> entityName:constEntityNameStarxid] ;
> if (!self) {
> [super dealloc] ;
> }
>
> return self ;
> }
To review, there are three points of possible failure in an init method:
- (id) init... {
// do some preparatory things
if (...preparatory things failed...) {
... error point #1 ...
}
self = [super init...];
if (!self)
... error point #2 ...
// do rest of initialization
if (...something goes wrong...) {
... error point #3 ...
}
Error point #2 is easy. Just return nil.
#3 is pretty easy. Clean up things you've already done in this method (such as
allocating memory), and invoke '[super dealloc]' before returning nil. This is
still slightly risky, because the super dealloc *could* end up invoking some
(override) method in this subclass, which -- not having been successfully
initialized -- could crash. But it's still the best choice, and you should try
to remember to code your subclass defensively, if you think this situation
might occur.
#1 is the hard one. You can't return nil, because that would leak the object's
memory. You can't call super's dealloc, because you don't know if super's
dealloc is safe to call if super's init hasn't executed. You can't call
release, because that might call dealloc. You can't free the object's memory
yourself, because you don't know how (unless you happen to know how it was
allocated, which in general you don't).
The best choice in a case like this is to avoid doing anything that might fail
before calling the super init. Or, throw an exception if it fails. Or, call one
of super's designated initializers anyway, then call super dealloc after it
returns. Or, I suppose, you could do the least wrong of all the wrong things,
which would probably be to return nil and leak the object deliberately.
But I don't really know a good answer for case #1.
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