objective c - How to choose the attributes of a @property in a nutshell? -

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• objective-c declared @property attributes (nonatomic, copy, strong, weak) 4 answers

how know attribute add @property ?

i got @property (strong) , @property (weak), think : strong if class "owns" referred-to instance ; weak if reference object existence not managed our current class.

if property created dragging-and-dropping interface builder, there cryptic unretain_unsafe or so. sounds complicated me, believe xcode knows does...

• i kind of understand retain, assign kind of deprecated...

• and better (compulsory) use copy nsstring attributes...

• but if want have @property int or enum ?

• shall choose weak attribute if @property points singleton ?

you see : so many questions theses attributes !

i thought nice have short , clear explanation of these attributes members here :)

a few notes in no particular order

• weak has additional features of being nil-ed out when referred-to object deallocated, never left dangling pointer garbage
• it not compulsory use copy semantics nsstring property, highly recommended. while nsstring immutable, property might set mutable string subclass, if don't want changing out under you, should use copy
• the rule of thumb scalar property types pretty simple: not reference counted, neither strong nor weak applies. can readonly or readwrite, depending on need.