Question

Well ! I got confused about the way of declaring variables & implementing its properties.

The .h File contents

@interface XYZAppDelegate : NSObject <UIApplicationDelegate> {

}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet XYZViewController *viewController;
@end

The .m File Contents

#import "XYZAppDelegate.h"
#import "XYZViewController.h"
@implementation XYZAppDelegate
@synthesize window=_window;
@synthesize viewController=_viewController;

My questions/Queries are as follows.

• Don’t we require to declare variables if we put property ? ( Using property, we can indirectly declare variable – is it like that ? )
• What are the additional features other than this ? ( In coding specific )
• Why does everybody insist to use _ before each property accessor ? ( Other than security threats ? Has it become coding standard ? Whats the reason behind it? )

Answer 1

• You do not have to declare the
  variable. It is done automatically,
  I believe by @synthesize. One
  advantage to declaring it is that the
  debugger will automatically list it.
  Weigh this against the ugliness of
  redundant definition.
• Other features: read only properties,
  assigned (unretained) values.
• The underscore is a convention for
  naming member variables that are
  differently named than properties and
  method variables. Apple’s samples
  sometimes use this convention and
  sometimes do not. I view it as
  usually unnecessarily verbose as a
  programmer can easily tell the
  difference between myVariable and
  self.myVariable.