Question

If I have a instance method and within this method I do something like this:

NSString *peopleString = [peopleList componentsJoinedByString: @", "];
...
UILabel *likeLabel = [[UILabel alloc] initWithFrame:CGRectMake(16.0+6.0f, 4.0f, 252.0f, 12.0f)];
[likeLabel setText:peopleString];
[likeLabel setFont:[UIFont fontWithName:@"Arial" size:12]];
[likeRow addSubview:likeLabel];
[likeLabel release];

The componentsJoinedByString doesn’t contain a new, copy or alloc, thus I don’t have to release it. What I’m wondering though is, when my peopleString gets deallocated. Might it happen to early? Meaning, before I can set the text in my label. Should I better use a [[NSString alloc] initWithString:[peopleList componentsJoinedByString: @", "]]; and release it at the end of this method?

Answer 1

When you create peopleString it gets reference count of 1. Later, when you tell likeLabel to use peopleString for its text, the reference count of peopleString is incremented by 1. Now the reference count for peopleString is 2. When likeLabel is released, presumably at the end of the event loop, the reference count of peopleString is decremented by 1. But your instance of peopleString is also getting its reference count decremented by 1 via the end of the event loop. So peopleString now has a reference count of 0 and is removed from memory.

See #6578 for a much better explanation.