Again about self and instance variables in Objective-C

Question

In some books, Apple's code samples and internet resources I noted direct accessing to ivar instead of using synthesized accessors. It seems to me that it's very often for UILabel, UITextFiled and UITextView.

@interface MagicViewController : UIViewController {
    UITextField *aField;
}
@property (nonatomic, retain) UITextField *field; 


@implementation MagicViewController

@synthesize aField; 

- (void) superMethod 
{
    aField.text = @"Bla-bla-bla";

    NSString *string = [NSString stringWithString:aField.text];
    NSLog(@"Ho-ho-ho %@", string);

}

The question: Is it safe for some reasons? Why they don't use

- (void) superMethod 
{
    self.aField.text = @"Bla-bla-bla";

    NSString *string = [NSString stringWithString:self.aField.text];

    NSLog(@"Ho-ho-ho %@", string);

}

Williham Totland · Accepted Answer · 2011-07-22 13:52:16Z

1

Not using the accessor guarantees that what you are accessing is, in fact, the ivar field, as a subclass could override .aField, supplying something else.

Wether this is what you want or not varies wildly.

That is one possible reason for the sample code to eschew accessors in favor of direct access, but precisely why it is done in any given case is not necessarily easy to know.

Another possible reason is that accessing the ivar is faster, and on iOS in particular, cycles are hard-won.

answered Jul 22, 2011 at 13:52

Williham Totland

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1 Comment

Michael Over a year ago

If you have a time and wish, could you give me a short sample where it's necessary to access to ivar directly. It would be much appreciated, because I've seen "never ever use direct access to ivar". And it's clear about faster accessing.

Peter DeWeese · Accepted Answer · 2011-07-22 13:52:28Z

0

Either way will work just fine in this particular case. They like to define everything out in references so you can see exactly what is happening.

answered Jul 22, 2011 at 13:52

Peter DeWeese

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