Objective-C instance variable vs @interface variable

Question

i'm new to iOS programming and its difficult to understand the difference about instance variable. I post you two example, could you explain me what is the difference? (only for instance variable that are not IBOutlet).

in .m file

@interface MyClass ()
  @property(nonatomic, strong) NSString *aString;
@end

in .m file

@implementation MyClass
{
   NSString *_aString;
}

In both cases i'm on .m file and i'm declaring "instance" variable. But, what is the difference of declaring them in @interface ( .m file ) and in @implementation with {} ?

I have excluded IBOutlet because there are in @interface only (i guess...)

Answer 1

The @interface variable is called a property - thus the @property.

Check out this source to find out the difference:

Difference between properties and variables