objective-c 引用计数

The rules are simple:

• Any object returned by 

  alloc

  , 

  copy

  , 

  copyWithZone

  , or 

  new

   has a retain count of 1.

• retain

   increases the receiving object's retain count.

• release

   decreases the receiving object's retain count.

• autorelease

   tells the current autorelease pool to send the receiving object the 

  release

   message “later”.
• Any factory method that doesn't have “new” or “copy” in the name (e.g., 

  stringWithString:

  ) returns an object that it has autoreleased on your behalf.

Or, digested a bit:

• Any method whose name contains 

  copy

  , 

  alloc

  , 

  retain

  , or 

  new

   returns an object that you own.
• Any method that doesn't, returns an object that you don't own.
• To own an object, retain it.

The incorrect implementation of 

setName:

 that you show is incorrect because it stores an autoreleased object in an instance variable, when you mean to own the object. You should retain it or, in this case, copy it. One way is to simply use 

alloc

 and 

initWithString:

, as in the correct example you show; the other way would be 

copy

.