Alloc init保留吗？

Question

Can anybody explain why the retain count of this line of code:

[[[SomeClass alloc] init] retain] 

Is two? I'm only calling retain once.

Answer 1

Because alloc adds 1 to the retain count. You should read Apple's Memory Management Programming Guide .

Answer 2

The retain count is two because [alloc] also increases the retain count. Strictly speaking the retain count of an object isn't just how many times you've called retain, but how many things are holding on to it.

Answer 3

If you create an object, using a method who's name begins with alloc, new, copy or mutableCopy , or you retain an object, its retain count is increased by 1

If you release or autorelease an object, it's retain count decreases by 1

In your example code, both alloc and retain increase the retain count by 1.

See Apple's docs for further details:

http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html