问题描述
两者有什么区别？
@property(unsafe_unretained) MyClass *delegate;
@property(assign) MyClass *delegate;
两者都是非归零弱引用，对吧？那么有什么理由我应该写更长更难阅读 unsafe_unretained 而不是 assign ？
Both are non-zeroing weak references, right? So is there any reason why I should write the longer and harder to read unsafe_unretained instead of assign?
注意：我知道弱这是一个归零参考。但它只有iOS> = 5.
Note: I know there is weak which is a zeroing reference. But it's only iOS >= 5.
推荐答案
在属性访问器中，是的，它们是相同的。对于这种情况， assign 属性将映射到 unsafe_unretained 。但是考虑手动编写ivar而不是使用ivar合成。
In a property accessor, yes those are the same. assign properties will map to unsafe_unretained for this case. But consider writing the ivar manually rather than using ivar synthesis.
@interface Foo
{
Bar *test;
}
@property(assign) Bar *test;
@end
这个代码现在在ARC下是不正确的，而在ARC之前它是'吨。所有Obj-C对象的默认属性是 __ strong 向前移动。推进这项工作的正确方法如下：
This code is now incorrect under ARC, whereas prior to ARC it wasn't. The default attribute for all Obj-C objects is __strong moving forward. The proper way to do this moving forward is as follows.
@interface Foo
{
__unsafe_unretained Bar *test;
}
@property(unsafe_unretained) Bar *test;
@end
或使用ivar合成只需 @property（unsafe_unretained ）Bar * test
or with ivar synthesis just @property(unsafe_unretained) Bar *test
所以它真的只是一种不同的写作方式，但它表现出不同的意图。
So really its just a different way of writing the same thing, but it shows a different intent.
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