On 3 May 2008, at 4:00 pm, Hrishikesh Muruk wrote:
If I make an NSArray in the following manner:
NSArray *newArray = [NSArray arrayWithArray:oldArray];
[newArray retain];
Now I it is my responsobolity to send a release message to newArray.
But am I responsible to send release messages to the contents of
newArray?
No, they are retained by the array, and are released when the array is
released.
How do I do a deep copy? If oldArray is an NSArray holding pointers
of type MyObj*. If I want a newArray that duplicates the contents of
oldArray. By that I mean I want the pointers in newArray to point to
new objects of type MyObj rather than the same objects as oldArray
how do I do this?
Would this work:
for(i=0;i<[oldArray count]; i++) {
MyObj *temp = [[oldArray objectAtIndex:i] copy];
[newArray addObject:temp];
}
But this requires MyObj to support the copy message. Do all objects
in cocoa automatically support copy message (if they inherit from
NSObject)?
No they don't - you have to implement copy if you claim to support the
NSCopying protocol for your own objects - but most Cocoa objects
themselves do implement it.
Is there an easier way to do deep copy of arrays?
You can use a category - I use the following, which allows you to do
something like arrayCopy = [oldArray deepCopy]; However it's not magic
- it just loops through and copies each object just as you do above -
the advantage is that it deals with nested arrays and dictionaries.
The disadvantage is that it *always* does this, for every object,
which might be a blunt instrument in some cases. In general, you want
to avoid the need to deep copy things.
(note deepCopy is implemented to follow copy semantics - caller is to
release the returned object).
@implementation NSDictionary (DeepCopy)
- (NSDictionary*) deepCopy
{
NSMutableDictionary* copy;
NSEnumerator* iter = [self keyEnumerator];
id key, cobj;
copy = [[NSMutableDictionary alloc] init];
while(( key = [iter nextObject]))
{
cobj = [[self objectForKey:key] deepCopy];
[copy setObject:cobj forKey:key];
[cobj release];
}
return copy;
}
@end
#pragma mark -
@implementation NSArray (DeepCopy)
- (NSArray*) deepCopy
{
NSMutableArray* copy;
NSEnumerator* iter = [self objectEnumerator];
id obj, cobj;
copy = [[NSMutableArray alloc] init];
while(( obj = [iter nextObject]))
{
cobj = [obj deepCopy];
[copy addObject:cobj];
[cobj release];
}
return copy;
}
@end
#pragma mark -
@implementation NSObject (DeepCopy)
- (id) deepCopy
{
return [self copy];
}
@end
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