iOS 5最顯著的變化就是增加了Automatic Reference Counting（自動引用計數）。ARC是新LLVM 3.0編譯器的特性，完全消除了手動內存管理的煩瑣。在你的項目中使用ARC是非常簡單的，所有的編程都和以前一樣，除了你不再調用retain, release, autorelease。啓用ARC之後，編譯器會自動在適當的地方插入適當的retain, release, autorelease語句。你不再需要擔心內存管理，因爲編譯器爲你處理了一切。注意ARC是編譯器特性，而不是iOS運行時特性（除了weak指針系統），它也不是其它語言中的垃圾收集器。因此ARC和手動內存管理性能是一樣的，有些時候還能更加快速，因爲編譯器還可以執行某些優化。
具體內容太多，就不列了，這裏列個目錄：
ARC完全指南 ................................................................................................................ 3
指針保持對象的生命............................................................................................. 3
Xcode的ARC自動遷移 ......................................................................................... 9
Xcode的自動遷移工具 ................................................................................... 9
轉換後的其它問題........................................................................................ 14
禁止某些文件的ARC ....................................................................................
14
ARC自動遷移的常見問題 ............................................................................ 15
屬性property ....................................................................................................... 17
IBOutlet .......................................................................................................... 18
readonly property .......................................................................................... 19
autorelease、release、retain調用 ..................................................................... 19
dealloc方法 .......................................................................................................... 20
AutoreleasePool .................................................................................................... 20
Toll-Free Bridging .................................................................................................. 21
Delegate 和 Weak Property ................................................................................ 26
unsafe_unretained ................................................................................................ 27
iOS 4中使用ARC .................................................................................................. 27
ARC高級指南 .............................................................................................................. 28
Blocks與ARC ........................................................................................................ 28
Singleton與ARC ................................................................................................... 34
Autorelease和AutoreleasePool .......................................................................... 40
Cocos2D 和 Box2D .............................................................................................. 45
靜態庫static library .............................................................................................. 48
最後？................................................................................................................... 49
參考資料............................................................................................................... 49
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