问题
Example iVar foo,
@property (nonatomic) NSString* foo; // inside .h
Option 1
@Synthesize foo; //Inside .m
foo = [[NSString alloc] init]; // viewDidLoad method
Option 2
@Synthesize foo; //Inside .m
self.foo = [[NSString alloc] init]; // viewDidLoad method
Option 3
@Synthesize foo = _foo; //Inside .m
_foo = [[NSString alloc] init]; // viewDidLoad method
Why?
At so many places I have seen code which has different ways of doing init an Object in Obj - C but which one is the best practise?
回答1:
In this regard, ARC is the same as MRC.
you have specified all these take place in viewDidLoad. in that case, use the setter (Option 2).
if you were to initialize/set in the initializer, then you would use direct access. the basic reason is that in the initializer (e.g. -init), you have a partially initialized object. during initialization, you want to focus on initializing variables your class needs or expects in order to function correctly. as well, you want to avoid side-effects you can encounter when using the accessors in partially constructed states.
in a fully constructed state (e.g. viewDidLoad), you should relegate the implementation to the accessors for correct behavior, as specified by your object's interface.
Additional Reading:
Initializing a property, dot notation
Should I refer to self.property in the init method with ARC?
Why would you use an ivar?
回答2:
I think you should understand the difference between these three and then decide which one is good for you.
option 1: Here while initializing you are not using the synthesizer method. so there is no use of declaring property-synthesizer in .h and .m
option 2: here you are using property-synthesizer. But the name of the method for accessing the instance and actual instance variable is same.
option 3: Here again you are not using the property-synthesizer method. Here foo is the name of the method and _foo is the actual instance.
In my opinion third one is the good. Since you the difference you can decide which one is good for you.
来源：https://stackoverflow.com/questions/12035149/what-is-the-correct-way-of-init-ivar-variables-in-presence-of-arc