Re: remove elements during the iteration on NSMutableDictionary

[Jonathan deWerd]

On Aug 6, 2008, at 10:49 AM, Andrew Merenbach wrote:

On Aug 6, 2008, at 9:30 AM, Roland King wrote:

for (id theKey in aDictionary) {
id anObject = [[aDictionary objectForKey:theKey] retain];

[aDictionary removeObjectForKey:theKey];

elements?

[anObject someMessage];
[anObject release];
}

// Question: will this removal break or corrupt the loop of enumerating the

Oops, I diid not see that, sorry.

Yup, that works. I prefer:




Amin

[id anObject = [[aDictionary objectForKey:theKey] retain] autorelease]; That allows breaks inside the loop. (And you do not forget the - release, as you did.)

or send it a message before you remove it from the dictionary.

for( id theKey in aDictionary ){

        id anObject = [[ aDictionary objectForKey:theKey ];

        [ anObject someMessage ];

        [ aDictionary removeObjectForKey:theKey ];
}

of course as the original response pointed out, you can't really do this anyway as the modification will cause an exception so you don't really have the problem, you can't really remove the object where you're removing it. One question I had, the mutable guard which raises the exception, that's only there because of the use of fast-enumeration, am I right? Had you used an NSEnumerator I believe it's still not safe to remove objects, but I don't think you get the exception, you just need to know you mustn't do it._______________________________________________

May I suggest the following?

-----

NSMutableArray *keysToRemove = [NSMutableArray array];
for (id theKey in aDictionary) {
        [keysToRemove addObject:theKey];
}
[aDictionary removeObjectsForKeys:keysToRemove];



Cheers,
        Andrew

You can even use -[NSDictionary objectsForKeys:notFoundMarker:] to send a single message to the dictionary's objects using - makeObjectsPerformSelector:

You could also use performSelector:withObject:afterDelay: assuming that you'll reenter the run loop before you need the objects removed.

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