Question

I have my ViewController.h/m and another class Keyboard.h/m.
In my ViewController.h I have an UILabel:

@interface ViewController : UIViewController{

UILabel *label;

}

@property (nonatomic, retain) IBOutlet UILabel *label;

and my ViewController.m looks so

#import "ViewController.h"
@synthesize label;
...

Now I want to change the label from Keyboard.m.
I have tried something like this:

#import "ViewController.h"
...
ViewController *vc;
vc.label.text = @"text";

it compiles without any errors but the label doesn’t change

Answer 1

It’s very error prone that you’re doing here.

ViewController *vc;

declares a pointer, but this won’t be initialized; so when you’re accessing its property vc.label.text, objc_messageSend() will be passed a bogus pointer, so it can potentially crash! (you’re lucky if id didn’t do so.)

Anyways: if you have done it well, like ViewController *vc = [[ViewController alloc] init]; creating a new instance wouldn’t have affected the other instance. You have to store the pointer to your instance somewhere, e. g. set a @property (retain) ViewContrller *vc; to your application’s app delegate object, and access it through that property like this:

[(MyAppDelegate *)[[UIApplication sharedApplication] delegate] vc].label.text = @"new text";

that way it should work.

Hope it helps.