原子属性和非原子属性有什么区别？ - What's the difference between the atomic and nonatomic attributes?

问题：

What do atomic and nonatomic mean in property declarations? 属性声明中atomic和nonatomic是什么意思？

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

What is the operational difference between these three? 这三个之间的操做区别是什么？

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解决方案：

参考一： https://stackoom.com/question/2TBq/原子属性和非原子属性有什么区别
参考二： https://oldbug.net/q/2TBq/What-s-the-difference-between-the-atomic-and-nonatomic-attributes