Difference between properties and variables in iOS header file? [duplicate]

Answer 1

Defining the variables in the brackets simply declares them instance variables.

Declaring (and synthesizing) a property generates getters and setters for the instance variable, according to the criteria within the parenthesis. This is particularly important in Objective-C because it is often by way of getters and setters that memory is managed (e.g., when a value is assigned to an ivar, it is by way of the setter that the object assigned is retained and ultimately released). Beyond a memory management strategy, the practice also promotes encapsulation and reduces the amount of trivial code that would otherwise be required.

It is very common to declare an ivar in brackets and then an associated property (as in your example), but that isn't strictly necessary. Defining the property and synthesizing is all that's required, because synthesizing the property implicitly also creates an ivar.

The approach currently suggested by Apple (in templates) is:

Define property in header file, e.g.:

@property (assign, readonly) gameCenter;

Then synthesize & declare ivar in implementation:

@synthesize gameCenter = __gameCenter;

The last line synthesizes the gameCenter property and asserts that whatever value is assigned to the property will be stored in the __gameCenter ivar. Again, this isn't necessary, but by defining the ivar next to the synthesizer, you are reducing the locations where you have to type the name of the ivar while still explicitly naming it.

Answer 2

When you define a property a getter and setter is created for you. When you access them usingobject.member setters and getters are called automatically.

When you declare variable in interface setters and getters are not written for you. you can also specify some visibility modifiers to them like @private,@public etc.

Answer 3

{
BOOL gameCenterAvailable;
BOOL userAuthenticated;
}

the above two are called member Variables They can't be accessed outside the class.(Important point) (unless you provide custom getters and setters)

if you make a @property then the variable can be read inside the class as well as outside the class..so the setters and getters are generated for you..automatically

then declaring the same as a member variable isn't required..

It is just done to increase Readability .. you can read it easily than reading

 @property (non..)