error: expected identifier or '(' before 'public' - objective C

I a开发者_如何学编程m getting this error when i declare my instance variable as

@interface FOO : NSObject
{
 @public
  int a;
}
@public
-(id)init;
-(void)dealloc;
@end

error: expected identifier or '(' before 'public'

You do not use @public or other access keywords outside the interface definition, as you don't declare public or private methods in Objective-C.

As long as you expose a method in a header/interface it's automatically publicly accessible from outside the class. If you only add an implementation, but don't expose it in the header/interface (or only expose it in a class extension), it's private.

@interface FOO : NSObject
{
@public
    int a;
}

- (id)init;
- (void)dealloc;

@end

Now why you would want to declare a public int a instance variable (instead of using a property) or explicitly declare two methods that NSObject already has is beyond me.

In objective-c methods block cannot contain @public (or @private) block - it is aplicable only to instance variable and all methods in objective-c classes are public, so to fix your error remove 2nd @public in your code:

@interface FOO : NSObject
{
 @public
  int a;
}
-(id)init;
-(void)dealloc;
@end