When declaring class properties/variables, can you just declare it via @property?

Question

I've noticed that some generated classes only declare class properties/variables via @property, and don't include them within the @interface, as such:

@interface AddItemViewController : UITableViewController {

}

@property (nonatomic, retain) UITextField *itemName;

I was just curious if that's an acceptable way to do it, or if that is done for different reasons?

I normally do this:

@interface AddItemViewController : UITableViewController {
  UITextField *itemName;
}

@property (nonatomic, retain) UITextField *itemName;

I declare it first in the @interface and then add the @property for it...

* Update *

I just wanted to update this a bit, because it's still not 100% clear to me.

I always thought that to declare a @property, you first needed to declare it within the @interface first, and then I saw this:

@interface mInventoryAppDelegate : NSObject <UIApplicationDelegate> {

}

@property (nonatomic, retain) IBOutlet UIWindow *window;

@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;

- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;

@property (nonatomic, retain) IBOutlet UINavigationController *navigationController;

@end

All of those @property declarations are declared only as @properties, and not within the @interface.

For example, if I had say NSString *myString - I can declare that in the @interface and not as a @property and still have access to it no problem, but the getters and setters won't be created. I could also declare it in both. But what if I just declare it as @property, as such:

@interface AddItemViewController : UITableViewController {

}

@property (nonatomic, retain) NSString *myString;

Notice how I didn't add it between the @interface { } - how does it differ.

Sorry for repeating, but I'm just trying to reword this so that I can get an answer that makes more sense to me.

Answer 1

With the "modern" runtime, which the iPhone uses, the compilers can create the instance variable for you. Just use:

@synthesize itemName;

or if you prefer...

@synthesize itemName=_itemName;

...in your implementation. The compilers will then create ivar 'itemName' or '_itemName'.

This is of course for the case that the property is a simple getter/setter for one particular instance variable.

EDIT: NVM, per @bbum, what I thought of in my mind as the "32-bit" sim is actually the older simulator that didn't behave like the new runtime. The newer simulator is still 32-bit, and supports this behavior. See his comment below.

update

In response to your updated question:

The "interface" for a class is everything up to the @end. I think what you are calling "interface" is actually just the instance variables within the {}. What is between the {} are the instance variables for your class. The whole @interface includes those instance variables PLUS the method and @property declarations between the {} and the @end.

So I think what you are really asking is if you have a @property in your @interface, and that @property is just a simple getter/setter pair, then do you need to declare a "backing" instance variable also in your @interface, within the {}.

The answer for iPhone is NO. The compilers (both) can create that instance variable for you.

I hope that answers the question?