objective-c - 如何理解ios中api支持的sdk版本？

Question

如函数+ (Class)layoutAttributesClass在ios10中可以使用（如果我没理解错的话），但是在真机中（sdk ios 9）测试依旧调用了+ (Class)layoutAttributesClass，这是怎么回事呢？

Answer 1

Answer 2

ABI&API requires staged planning and implementation
If an API does not appear in the document, it does not necessarily mean it has not been implemented. It may be private
You may have met a fake Apple