Question

I’ve been teaching myself Objective C recently, and have noticed the following pattern used a lot in tutorials and sample code (including samples from the Apple site).

UIView *myUiView = [[UIView alloc] init];
self.uiView = myUiView;
[myUiView release];

I was just wondering though, it seems a bit of a waste to create a new variable, just to set a property. I’ve also seen the following pattern used too, but from what I understand its considered bad form to use autorelease on an iOS device as the autorelease pool takes up quite a bit of overhead which might not be good on a mobile device

self.uiView = [[[UIView alloc] init] autorelease];

I’ve been toying with using the following pattern recently, which sets the property, and then calls release on the property (to decrease the reference counter on the property itself).

self.uiView = [[UIView alloc] init];
[self.uiView release];

I’ve managed to use it on a few ViewControllers with no ill effects, but is this valid code, or am I missing something which makes it a bad idea?

Answer 1

The property getter is a method, and it does not have to return an ivar, it may actually get its return value anywhere, so you could release that, but it could be an autoreleased value already. If that is the case, you’re in trouble.

IOW, if a property getter would do something like (not usual, but possible and valid):

- (NSString *) helloString
{
    return [[myStringIVar copy] autorelease];
}

and you do:

[self.helloString release];

then you failed in two ways:

• You did not release the ivar you wanted to release
• You release an autoreleased object

IMO, it is better to release the ivar directly:

[myStringIVar release];