Objective C: Should I assign the variable AND create a property or is just one of them enough?

Question

I have got a header file (.h) and I want to declare name but all these ways work the same I think because I haven't seen any difference with functionality. Could you tell me what the difference is between:

This with both declarations:

@interface someClass : UIViewController
{
    NSString *name;
}

@property (nonatomic, copy) NSString *name;

@end

Without variable:

@interface someClass : UIViewController
{

}

@property (nonatomic, copy) NSString *name;

@end

Or Without property:

@interface someClass : UIViewController
{
    NSString *name;
}

@end

Answer 1

   @interface someClass : UIViewController
   {
     NSString *name;
   }

   @property (nonatomic, copy) NSString *name;

   @end

Doing this you will explicitly declare both a property and an ivar.

A property is just a set of methods:

 - (void)setName:(NSString*)name;
 - (NSString*)name;

An ivar is the memory store holding the value that the property methods manage. This allows you to do:

self.name = ... // access through setter method
name = ... // direct access

The advantage of using properties is that they deal with memory management for you. E.g., in your case, the property is of type copy: this means that with the first syntax (self.name = ...) a copy of the object will be done. If not using properties, you would explicitly need to do: name = [originalString copy]; to obtain the same effect.

Other options you can specify for properties (but not ivars) are: strong and weak ownerships.

Furthermore, a property also represents a public interface to access the variable from outside your class.

Using direct access you are on your own as to memory management (if you are not using ARC). If you are using ARC and don't define properties, you will not be able to control how the memory is managed by specifying the ownership: strong, weak, retain).

 @interface someClass : UIViewController
 {

 }

 @property (nonatomic, copy) NSString *name;

 @end

Here you only declare the properties; the ivar is "inferred" by the @synthesize directive in your implementation file. This is only possible in Objective C 2.0 and later (previously, the ivar declaration as above was mandatory).

The same considerations as above applies, with a minor nuance: with older versions of LLVM (ObjC compiler) you will not be able to reference directly the auto-synthesized ivar; with current version of LLVM, if you omit the @synthesize directive, then an automatic ivar named after your property would also be declared (in your case it would be _name).

This last paragraph may seem a bit "advanced", or contrived, but you can safely ignore it.

 @interface someClass : UIViewController
 {
    NSString *name;
 }

 @end

In this case you are only declaring the ivar. No accessor methods. You will need to handle memory management on your own (if not using ARC), futhermore you will not be able to access the variable from outside the class. For that you need accessors.

Hope this helps.

Answer 2

Case 1:

The is the old method, here the @property and variable are not related until you @synthesize name = name;

Access methods : variable : name = @"hello"; //direct access to viariable

setter/getter : self.name = @"hello" // set value to name using setName: selector

With the latest xcode just the property is enough.

Case 2: the new xcode style. Here the synthesize and variable creation is taken care by the compiler. (so less 2 lines of code and this also helps with memory management)

Access methods : variable : _name = @"hello"; //direct access to viariable

setter/getter : self.name = @"hello" // set value to name using setName: selector

Case 3: Here the name is just a variable and it dose not have a setter or a getter. with out property (or) setter & getter this is as good as a local variable and it cannot be accessed from other objects.