CODEWITHSUNDEEP
iphoneobjective-ccocoa-touchproperties
Sreejit
Sreejit

Reputation: 107

Ambiguity with Objective C Properties

I have gone through many questions asked here and on other forums regarding @property in Objective-C. But a question pops up every now and then..

Do we need i-vars to support properties?

Please go through the following code -

the RootViewController.h file :-

#import <UIKit/UIKit.h>

@interface RootViewController : UIViewController {

}

@property (nonatomic, retain) NSMutableArray *arrTest;

@end

The RootViewController.m is as follows - 

#import "RootViewController.h"

@implementation RootViewController
@synthesize arrTest;

#pragma mark -
#pragma mark View lifecycle


- (void)viewDidLoad {
    [super viewDidLoad];

    self.arrTest = [[[NSMutableArray alloc] init] autorelease];

    [arrTest addObject:@"Object1"];
    [arrTest addObject:@"Object2"];
    [arrTest addObject:@"Object3"];
    [arrTest addObject:@"Object4"];
    [arrTest addObject:@"Object5"];

    NSLog(@"arrTest :- \n%@",arrTest);
    NSLog(@"self.arrTest :- \n%@",self.arrTest);


    [self.arrTest addObject:@"Object6"];
    [self.arrTest addObject:@"Object7"];
    [self.arrTest addObject:@"Object8"];
    [self.arrTest addObject:@"Object9"];
    [self.arrTest addObject:@"Object10"];

    NSLog(@"arrTest :- \n%@",arrTest);
    NSLog(@"self.arrTest :- \n%@",self.arrTest);

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;

}

As you can see, I have not created an instance variable to support the property.

From this I am assuming that a variable is internally created as I can access it by just saying

[arrTest addObject:@"Blah Blah"];

If that is the case, then why do we need to create instance variable if we are about to declare properties?

Upvotes: 2

Views: 613

Answers (1)

Nick Moore
Nick Moore

Reputation: 15857

If your @property declaration references an undeclared ivar, the Objective-C runtime will dynamically synthesize the ivar for you.

This requires that you compile for iPhone OS or 64-bit Mac OS X. If you want to target Mac OS X i386 or PPC you have to declare your ivars explicitly.

There is a good article about this here. http://cocoawithlove.com/2010/03/dynamic-ivars-solving-fragile-base.html

Upvotes: 3

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