我们在 ARC 中创建对象的这两种方式有什么区别吗？

Question

I am wondering is there actually any difference between:

UIButton *deleteButton = [UIButton buttonWithType:UIButtonTypeCustom];
self.deleteButton = deleteButton;

and:

self.deleteButton = [UIButton buttonWithType:UIButtonTypeCustom];

when using ARC ?

I see many people wrote a lot of code as in the first case, but I believe the second way is shorter and more clear and concise.

Answer 1

is there actually any difference between

Yes, but, under compiler optimization, generated binary would be identical.

UIButton *deleteButton , that is, UIButton __strong *deleteButton has ownership of the object.

The object was registered on the current Autorelease Pool because buttonWithType: class method does not begin with "alloc", "new", "copy", or "mutableCopy".

Thus,

UIButton *deleteButton = [UIButton buttonWithType:UIButtonTypeCustom];

/*
 * The current Autorelease Pool has ownership of the object. retainCount=1
 * __strong deleteButton has ownership of the object as well. retainCount=2
 */

self.deleteButton = deleteButton;

/*
 * If self.deleteButton is strong property, it has ownership of the object too. retainCount=3
 * If self.deleteButton is weak property, it doesn't have ownership of the object. retainCount=2
 */

Answer 2

Not an ARC expert or anything here, but I believe the code is identical. When you assign to a pointer, you're assigning the memory address that the pointer points to. The only thing you're doing in the top one versus the bottom one is saving the memory address in a local pointer before assigning it to self.deleteButton.