Using delegate between two viewcontrollers in iphone - iphone

Question

I have two view controllers: view controller and viewcontroller2nd. I have UILabel in one of them and would like to change it when the button( named Go) in the viewcontroller2nd is clicked. I am using delegates and protocols to do it.
The code looks like this:
ViewController.h
#import <UIKit/UIKit.h>
#import "ViewController2nd.h"
#interface ViewController : UIViewController <SecondViewControllerDelegate>
{
IBOutlet UILabel *lbl;
ViewController2nd *secondview;
}
-(IBAction)passdata:(id)sender;
#end
ViewController.m
#import "ViewController.h"
#import "ViewController2nd.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(void) changeLabel:(NSString*)str{
lbl.text = str;
}
-(IBAction)passdata:(id)sender{
ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
[self presentViewController:second animated:YES completion:NULL];
}
#end
Viewcontroller2nd.h
#import <UIKit/UIKit.h>
#protocol SecondViewControllerDelegate <NSObject>
#optional
-(void) changeLabel:(NSString*)str;
#end
#interface ViewController2nd : UIViewController{
IBOutlet UIButton *bttn;
id <SecondViewControllerDelegate> delegate;
}
#property (retain) id delegate;
-(IBAction)bttnclicked;
-(IBAction)back:(id)sender;
#end
ViewController2nd.m
#import "ViewController2nd.h"
#import "ViewController.h"
#interface ViewController2nd ()
#end
#implementation ViewController2nd
#synthesize delegate;
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(IBAction)bttnclicked{
[[self delegate] changeLabel:#"Hello"];
}
-(IBAction)back:(id)sender{
[self dismissViewControllerAnimated:YES completion:NULL];
}
#end
The passing of the control between the two views is working correctly. However, when i click the go button in the viewcontroller2nd, it doesn't change the value of the label to Hello. What is wrong with the code? Need some guidance.

Answer 1

It seems you never set the delegate.
You can do it in your passData method :
-(IBAction)passdata:(id)sender{
ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
second.delegate = self;
[self presentViewController:second animated:YES completion:NULL];
}

Answer 2

Hm, try the following in your changeLabel delegate method:
-(void) changeLabel:(NSString*)str{
lbl.text = str;
[lbl setNeedsDisplay];
}
EDIT:
Other than that:
Your label is a IBOutlet, right? Did you connect the label in your xib with the IBOutlet property (i.e. lbl) correctly in interface builder with the files owner

Answer 3

If you want to do this by using delegates then change passdata like:
-(IBAction)passdata:(id)sender
{
ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
[second setDelegate:self];
[self presentViewController:second animated:YES completion:NULL];
}
You can do this without delegates.
Just create a object of ViewController in secondView and synthesize it like:
#import "ViewController.h"
#interface ViewController2nd : UIViewController
{
IBOutlet UIButton *bttn;
ViewController *parent;
}
#property (nonatomic, assign) ViewController *parent;
-(IBAction)bttnclicked;
-(IBAction)back:(id)sender;
#end
and in the passdata change it like
-(IBAction)passdata:(id)sender
{
ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
[second setParent:self];
[self presentViewController:second animated:YES completion:NULL];
}
and change the bttnclicked like:
-(IBAction)bttnclicked
{
[parent changeLabel:#"Hello"];
}

Answer 4

I wrote following for you!
#import <UIKit/UIKit.h>
#interface ViewController : UIViewController
#property (strong, nonatomic) IBOutlet UILabel *label;
#end
#import "ViewController.h"
#import "ViewController2.h"
#interface ViewController () <ViewController2Delegate>
#end
#implementation ViewController
-(void)passdata:(NSString *)data
{
self.label.text = data;
}
- (IBAction)buttonClicked:(id)sender {
ViewController2 *v = [[ViewController2 alloc] initWithNibName:#"ViewController2" bundle:nil];
v.delegate = self;
[self presentViewController:v animated:YES completion:nil];
}
#end
#import <UIKit/UIKit.h>
#protocol ViewController2Delegate <NSObject>
- (void)passdata:(NSString*)data;
#end
#interface ViewController2 : UIViewController
#property(assign, nonatomic) id<ViewController2Delegate> delegate;
#end
#import "ViewController2.h"
#interface ViewController2 ()
#end
#implementation ViewController2
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
- (IBAction)buttonClicked:(id)sender {
[self.delegate passdata:#"hello"];
}
- (IBAction)backButtonClicked:(id)sender {
[self dismissViewControllerAnimated:YES completion:nil];
}
#end

Answer 5

You don't need to import the header "ViewController2nd.h" in the both ViewController.h and ViewController.m
You declare the UILabel without property like, #property (strong, nonatomic).
May be, You didn't properly map the UILabel to your .storyboard or .xib file.
You forget to assign the second view controller delegate while calling the controller
ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
second.delegate = self;
[self presentViewController:second animated:YES completion:NULL];
If anyone is using storyboard for viewcontrollers navigation.
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier hasPrefix:#"view_to_capture"]) {
ViewController2nd *destination = segue.destinationViewController;
destination.delegate = self;
}
}