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IPhone Properties

I'll have a few simple questions to make sure I'm using properties right in my application. I have read a lot on the internet but it is still unclear. Thanks a lot for any help or suggestions.

(1) I'm not entirely sure what this statement is and why it is needed.

@synthesize personName = _personName;

Why do you need the _personName variable? What is the advantage of this rather than just creating a property and synthesizing that personName variable.

@property (nonatomic, retain) NSString *personName;

(2) My application should be able to access the self.personName property variable or use the _personName variable. I believe self.personName is correct by then why does _personName exist even there?

(3) Also I'm a little confused about which variable I should post in dealloc () and which variable I should set to nil in viewDidLoad (). I also don't know if changes should be made to the didReceiveMemoryWarning () method.

@interface ViewController : UIViewController
{
    NSString *_personName;
}

@property (nonatomic, retain) NSString *personName;

@end



@implementation ViewController

@synthesize personName = _personName;

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.personName = [[NSString alloc] initWithString:@"John Doe"];

    NSLog(@"Name = %@", self.personName);
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
}

- (void)dealloc
{
    [super dealloc];
}

@end
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1 answer 


@synthesize personName = _personName;


  • This statement creates accessor methods for the property personName

    . You indicated that accessors should use an instance variable named _personName

    . If you just had @synthesize personName;

    , you would use personName

    accessors as an instance variable instead .

  • Usually you should use accessor methods like in self.personName

    or somePerson.personName

    or somePerson.personName = @"Joe";

    . If you don't care what the name of the ivar that the property supports personName

    , you don't need to specify it.

  • Use the accessor to -viewDidLoad

    , as in: self.personName = nil;

    . The same goes for -didReceiveMemoryWarning:

    . Whether to use an ivar or a property in -dealloc

    is controversial and somewhat a matter of taste. The main problem with using property accessors -dealloc

    is that it can cause problems if your class is a subclass and the accessors are overridden. Often times you don't need to worry about this because you know your class will not be subclassed.

  • Setting Ivar to zero upon release is also controversial. Many people think this is good style, others think it is a waste of time. Use your best judgment. This is certainly not necessary, but rather what some consider a good home.

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