Question

I’m new to objective-c and I always have problem with global variable . I don’t know where to initialize them . My problem is with an NSString . I wrote this code –

in .h

NSString *session ; // i also  @property(retain,nonatomic) and synthesize ...

in viewDidLoad , ‘

session=@"HEllo";

and in

-(IBAction) showInformations:(id)sender;
{
    NSLog(@" informations ok");
    NSLog(@"my sesison : %@  ",session);
}

But I have a crash in show information :/ session is empty I think . Help please

Answer 1

session = @"hello";
self.session = @"hello";

There is a huge difference between the above two statements. The first one just assigns hello to session. Here the string hello is autoreleased, so session is not valid when you tap the button, as you have not retained session. But in 2nd line self is used. When self is used, it is not just a simple assignment, it is actually a call to accessor method. Here you have used retain in property declaration. So when self is used, the setter for session is called which retains it. So session is valid when you tap the button.

The summery is use right property and use self to avoid many memory problems.

EDIT: As pointed by fluchtpunkt, this explanation is not valid for string literals. I was out of my mind that string literals are special when writing this.