IOS ARC - weak and strong properties

Question

I am trying to understand how ARC works, and as far as I know, I have to do something wrong here. This is the code I'm using:

Interface:

@interface ViewController : UIViewController{

}

@property (strong, nonatomic) NSString * myString ; 
@property (weak, nonatomic) NSString * myPointer ;

Implementation:

 - (void)viewDidLoad{

     [super viewDidLoad];
     self.myString = @"Hello world!" ; // myString is strong
     self.myPointer = self.myString ; // myPointer var is weak

     [self performSelector:@selector(makeNilMyValue) withObject:nil afterDelay:1];    
     [self performSelector:@selector(printValues) withObject:nil afterDelay:2];    
}

 - (void) makeNilMyValue{
     self.myString = nil ; 
}

 - (void) printValues{
     NSLog(@"myString: %@", self.myString) ;
     NSLog(@"myPointer: %@", self.myPointer) ; 
 }

After doing this, I get:

2012-02-26 11:40:41.652 test1[933:207] myString: (null)

2012-02-26 11:40:41.653 test1[933:207] myPointer: Hello world!

If I'm not mistaken, due to the weak myPointer, it should not save the contents of the object. Thus, it should show nil instead of "Hello World!"

What am I doing wrong?

After Caleb's answer, I created another weak pointer, see the code below:

- (void)viewDidLoad{
    [super viewDidLoad];
    self.myString = @"Hello world!" ; // myString is strong
    self.myPointer = self.myString ; // myPointer var is weak
    self.myPointer2 = self.myString ; // myPointer2 var is weak

    [self performSelector:@selector(makeNilMyValue) withObject:nil afterDelay:1];    
    [self performSelector:@selector(printValues) withObject:nil afterDelay:2];    
}

- (void) makeNilMyValue{
    self.myPointer2 = @"value changed!" ;
    self.myString = nil ;

}

- (void) printValues{
    NSLog(@"myString: %@", self.myString) ;
    NSLog(@"myPointer: %@", self.myPointer) ;
}

The fact is that I still had the same answer that I had:

2012-02-26 12:08:13.426 test1[1333:207] myString: (null)
2012-02-26 12:08:13.427 test1[1333:207] myPointer: Hello world!

Answer 1

As Caleb noted, using the NSString constant for this example is not a good idea.

- Objective-C @ "...":

NSString * temp = @ "/tmp/scratch"; , , -, 7- ASCII. . , , , , . , :

BOOL same = [@ "" isEqualToString: myString];

documentation , .

- . NSObject .

:

@interface ViewController : UIViewController

@property (strong, nonatomic) NSObject * myString; 
@property (weak, nonatomic) NSObject * myPointer;

@end

:

@implementation ViewController

@synthesize myString = _myString;
@synthesize myPointer = _myPointer;

- (void)viewDidLoad{

    [super viewDidLoad];

    self.myString = [[NSObject alloc] init];
    self.myPointer = self.myString;
    self.myString = nil; 
    NSLog(@"myString: %@", self.myString);
    NSLog(@"myPointer: %@", self.myPointer);
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

, , - Apple Developer llvm.

__ weak , . , .

Answer 2

, nil "Hello World!".

, "@" Hello World! " . ​​ .