可可记忆管理问题

Question

I am in an argument with a friend who says that I have to put autorelase here:

NSURL *url = [[NSURL URLWithString:@"http://origin-www.metrolyrics.com/api/widgets/mac/seeker.php"] autorelease];

But isn't the object automatically autoreleased when it was send to me from NSURL class method? Thanks.

Answer 1

This is the rule:

If you invoke a method that returns an object and:

• begins with new
• begins with alloc
• is retain
• contains copy

then you are responsible for releasing (or autoreleasing) the returned object. The only time this would not be the case is if the documentation says otherwise. You may also see in the header files that the method is annotated with the NS_RETURNS_RETAINED macro. (The header file counts as documentation)

An easy way to remember this is "NARC" (new-alloc-retain-copy).

In your example, since URLWithString: does not begin with new or alloc , does not contain copy , and is not retain , then you must not release the returned object. Doing so is a violation of the memory management guidelines and will cause your app to crash (unless you're doing something stupid elsewhere).

Answer 2

You are right. you did not allocate or copy an object so you do not have to release it. Just use your code without the autorelease. ;-)

The Class method you used looks like this: (Normally it does. We can't know it, because Apple doesn't share the code.)

+(id)URLWithString:(NSString *)aString {
    return [[[self alloc] initWithString:aString] autorelease];
}