Understanding ios and objective-c #property [duplicate] - ios

Question

This question already has answers here:
What is the difference between ivars and properties in Objective-C
(2 answers)
Closed 8 years ago.
What is the difference between:
#interface PhotoAppViewController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate>
{
UIImageView * imageView;
UIButton * choosePhotoBtn;
UIButton * takePhotoBtn;
}
#property (nonatomic, retain) IBOutlet UIImageView * imageView;
#property (nonatomic, retain) IBOutlet UIButton * choosePhotoBtn;
#property (nonatomic, retain) IBOutlet UIButton * takePhotoBtn;
And this:
#interface PhotoAppViewController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate>
#property (nonatomic, retain) IBOutlet UIImageView * imageView;
#property (nonatomic, retain) IBOutlet UIButton * choosePhotoBtn;
#property (nonatomic, retain) IBOutlet UIButton * takePhotoBtn;
What do the curly braces mean after the delegation?

Answer 1

From http://rypress.com/tutorials/objective-c/properties.html:
An object’s properties let other objects inspect or change its state.
But, in a well-designed object-oriented program, it’s not possible to
directly access the internal state of an object. Instead, accessor
methods (getters and setters) are used as an abstraction for
interacting with the object’s underlying data.
Stackoverflow Answer

Answer 2

The "curly braces" are the scope in which instance variables, (also known as ivars) are defined. Properties are variables that can be publicly accessed (i.e. by other classes), whereas instance variables are private and can be only accessed in the scope of the class's implementation itself.
Read this and this to get an intuitive understanding about the differences between properties and ivars.
I'd strongly recommend reading Apple's documentation on Objective-C, or a good book on the same topic if the former turns out to a tad bit too technical for your taste.