OC property 屬性設(shè)置解釋

This link has the break down

http://clang.llvm.org/docs/AutomaticReferenceCounting.html#ownership.spelling.property

assign implies __unsafe_unretained ownership.

copy implies __strong ownership, as well as the usual behavior of copy
semantics on the setter.

retain implies __strong ownership.

strong implies __strong ownership.

unsafe_unretained implies __unsafe_unretained ownership.

weak implies __weak ownership.

具體可參考獅子書 XD

一般實(shí)踐：

delegate -> weak

IBOutLet -> weak

int, BOOL -> assign

copy 有點(diǎn)特殊，主要針對NSString

1.定義NSString的指針，當(dāng)源字符串是NSString時(shí)，不管是copy還是string都是淺拷貝。

2.定義NSString的指針，當(dāng)源字符串是NSMutableString時(shí)，strong是淺拷貝，而copy是深拷貝。這樣，當(dāng)有人從NSMutableString那邊修改時(shí)，用了copy的NSString因?yàn)槭巧羁截?，就不會被影響，而strong的話就會發(fā)現(xiàn)明明是NSString卻被改變了，所以建議使用copy。