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__block 的解释以及在 ARC 和 MRC 下有什么不同？ #43

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tbfungeek opened this issue Jan 7, 2020 · 0 comments

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tbfungeek commented Jan 7, 2020 •

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MRC 环境下，block 截获外部用 __block 修饰的变量，不会增加对象的引用计数
ARC 环境下，block 截获外部用 __block 修饰的变量，会增加对象的引用计数

所以，在 MRC 环境下，可以通过 __block 来打破循环引用，在 ARC 环境下，则需要用 __weak 来打破循环引用。

见ARC和MRC下Block的使用注意

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