Question

i need help to read variable from one to another class. I have followed some answers about this but with no success.

PP.h:

@interface PP : UIViewController
{
@public int fNum;
}

@property (readwrite, nonatomic) int fNum;

- (IBAction)setSomeNum;

@end

PP.m:

@synthesize fNum;

- (IBAction)setSomeNum
{
fNum = 69;
NSLog(@"Set Num Activated %d",fNum); //OK
}

TryView.m:

#import "TryView.h"
#import "PP.h"

@interface TryView ()

@end

@implementation TryView
- (void)viewDidLoad
{
[super viewDidLoad];

PP *obj ;
int x = obj.fNum;
NSLog(@"Happines %d",x); //Prints 0
}
@end

What is wrong, why it prints 0?

Answer 1

What you’re doing is essentially undefined behavior, so be glad it didn’t crash.

PP *obj ;
int x = obj.fNum;

is fundamentally wrong – you are not creating/initializing the object, so obj is a dangling pointer, it can point anywere (i. e. to garbage) and crash when accessed. Even if you created the object, you should have called the setSomeNum method on it – it doesn’t get automagically called (why should it?). All in all, you have to write this:

PP *obj = [[PP alloc] init];
[obj setSomeNum];
int x = obj.fNum;

etc.