Question

Maybe someone could explain the difference between property:

in .h file

@property(nonatomic,retain) NSString *someString;
@property(nonatomic,retain) NSString *someString2;

in .m file

@synthesize someString = _someString;

or

@synthesize someString2;

what is the difference for _someString and self.someString2 using in controller?
and in dealloc how i should release these property’s

[_someString release];

AND

[self.someString2 release];

OR

_someString = nil;
_someString2 = nil;

Answer 1

After:

property(nonatomic,retain) NSString *someString;
property(nonatomic,retain) NSString *someString2;

and:

@synthesize someString = _someString;
@synthesize someString2;

someString is a property backed by the instance variable _someString. Memory retention and release is managed by Obj-C.

• Assignments to someString should use the form self.someString within the class, and must use <reference>.someString outside of it. Except within an initializer there should never be any assignments to a plain _someString.
• Reading the value can use simply _someString within the class, but self.someString is also valid, and must use <reference>.someString outside of it.
• Releasing the value must use the form self.someString = nil within the class, and <reference>.someString = nil outside of it.

someString2 is similar except it is backed by an automatically named instance variable, which happens to be called someString2.