Question

New to Objective-C, and i am basically from c++ background. I am learning now objective-c and would like to get confirmation of what i understood is write or wrong?. Kindly advise.

I have the following class:

@interface Test: NSObject
{
 int instance1; 
}
@property int instance1;
 - (void)  sayHello;
@end

Class ‘Test’ has a instance variable instance1. If the member function ie: sayHello wants to access the variable, it has to happen through getter/setter functions. So, There are two ways to get it :

1. User can define.
2. We can get the help from the compiler?. How?.
   declare the same variable as a property, and synthesize it, the the compiler
   gets the code of getter/setter for us for that particular variable.

So, Untimately, getter/setter is the only way to access the variable in the method implementation, ie. both self.instance1 = 100; and instance1 = 100 need getter/setter.

Having missed both 1. and 2., there is no way to access the instance1 variable.

Also, instance1 is a pubic variable can can be accessed outside of the class with object instance.

Test *t = [[ Test alloc] init];
t.instance1 = 200;

Questions:

1. Is there any way to make instance1 is “private”, so that I can not access the instance
   variable outside the class?
2. Is there anything wrong in my understanding?

Answer 1

If the member function ie: sayHello wants to access the variable, it has to happen through getter/setter functions.

It doesn’t have to. You can access ivars directly, without using accessor methods:

- (void)sayHello {
   instance1 = 123;
}

You can define private ivars by declaring them in the implementation file, not the header:

@implementation Test {
   int privateVar;
}
// ... additional implementation, methods etc.
@end

Note, that since Xcode 4.4 you don’t have to declare your ivars anymore. You simply declare a property. The ivar and the accessor methods will be synthessized automatically.

For more details, I recommend reading my answer to this question: Declaration of variables