Question

These both work in my app without any noticeable difference:

1)

theArray = [[NSMutableArray alloc] initWithArray:[NSKeyedUnarchiver unarchiveObjectWithData:theData]];

2)

theArray = [NSMutableArray arrayWithArray:[NSKeyedUnarchiver unarchiveObjectWithData:theData]];
[theArray retain];

However, are they really equivalent? (1) has an alloc statement, whereas (2) does not. Is one preferable over the other?

Answer 1

The effect is the same. But (2) is less efficient (a convenient method = alloc + init + autorelease).

1. alloc → init
2. alloc → init → autorelease → retain

The preferred way is not to copy the array.

theArray = [[NSKeyedUnarchiver unarchiveObjectWithData:theData] retain];

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BTW, I notice that you have been asking a lot of basic questions about iPhone OS development. Please go through the tutorials on these first.