Updating ViewController UILabel from another class - ios

Question

I'm new to development and been trying to figure this out,but after trying various different solutions, I'm still unable to get the result I'm looking for.
I would like to update the UILabel in a ViewController from another class.
here is a little demo program that I cannot get to work.
I have a view controller which has 3 UILabels, one is updated from the viewDidLoad and the other two I would like to update from the other class called Hello which is called from ViewController, I can the see the class is being called correctly as the console is logging the NSLog entry but I cannot get the syntax for updating the UILabel.
Thanks in advance.
ViewController.h
#import <UIKit/UIKit.h>
#interface ViewController : UIViewController
#property (nonatomic, retain) IBOutlet UILabel *firstLabelBox;
#property (nonatomic, retain) IBOutlet UILabel *secondLabelBox;
#property (nonatomic, retain) IBOutlet UILabel *thirdLabelBox;
#end
ViewController.m
#import "ViewController.h"
#import "Hello.h"
#interface ViewController ()
#end
#implementation ViewController
#synthesize firstLabelBox;
#synthesize secondLabelBox;
#synthesize thirdLabelBox;
- (void)viewDidLoad {
[super viewDidLoad];
firstLabelBox.text=#"Hello";
[Hello updatedisplay];
[Hello getStringToDisplay];
}
#end
Hello.h
#import <Foundation/Foundation.h>
#class ViewController;
#interface Hello : NSObject
+(void)updatedisplay;
+(void) getStringToDisplay;
#end
Hello.m
#import "Hello.h"
#import "ViewController.h"
#implementation Hello
+ (void)updatedisplay
{
NSLog(#"NewClass - updatedisplay");
ViewController *labelupdate02 = [[ViewController alloc]init];
labelupdate02.secondLabelBox.text = #"Apple";
}
+ (void) getStringToDisplay
{
NSLog(#"Inside getString function - updatedisplay");
ViewController *labelupdate03 = [[ViewController alloc]init];
labelupdate03.thirdLabelBox.text = #"World";
}
#end

Answer 1

First update method of Hello class
+ (void)updatedisplay
{
NSLog(#"NewClass - updatedisplay");
[[NSNotificationCenter defaultCenter] postNotificationName:#"CHANGE_SECOND_LABEL" object:nil];
}
+ (void) getStringToDisplay
{
NSLog(#"Inside getString function - updatedisplay");
[[NSNotificationCenter defaultCenter] postNotificationName:#"CHANGE_THIRD_LABEL" object:nil];
}
And then update viewDidLoad()
- (void)viewDidLoad
{
[super viewDidLoad];
firstLabelBox.text=#"Hello";
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(secondLabel) name:#"CHANGE_SECOND_LABEL" object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(thirdLabel) name:#"CHANGE_THIRD_LABEL" object:nil];
[Hello updatedisplay];
[Hello getStringToDisplay];
}
Implement below methods in ViewController.m.
- (void)secondLabel
{
secondLabelBox.text = #"Apple";
}
- (void)thirdLabel
{
thirdLabelBox.text = #"World";
}