原子屬性和非原子屬性有什麼區別？ - What's the difference between the atomic and nonatomic attributes?

問題：

What do atomic and nonatomic mean in property declarations? 屬性聲明中atomic和nonatomic是什麼意思？

@property(nonatomic, retain) UITextField *userName;
@property(atomic, retain) UITextField *userName;
@property(retain) UITextField *userName;

What is the operational difference between these three? 這三個之間的操做區別是什麼？

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解決方案：

參考一： https://stackoom.com/question/2TBq/原子屬性和非原子屬性有什麼區別
參考二： https://oldbug.net/q/2TBq/What-s-the-difference-between-the-atomic-and-nonatomic-attributes