Change UILabel text from subview using delegate - ios

Question

I have a view with a label in it. The lower side of this view is filled with a subview which has it’s own view controller. This subview has a button. My goal: I want to change the label by pressing the button in the subview.
I have tried the code beneath. It works fine when I let the ViewWillAppear method of the delegate call the ‘doSomeTask’ method of the SubviewController. A timer begins to count and after a few seconds, the SubviewController calls the delegates changeLabel method, and the label is changed. However, when I call the ‘doSomeTask’ method manually by pressing the button, the delegate isn’t listening. The call doesn’t reach the changeLabel method.
Probably I am doing something ridiculously stupid here. Forgive me, I’m just learning iOS programming. Thanks in advance for all the feedback.
MyViewController.h
#import <UIKit/UIKit.h>
#import "MySubViewController.h"
#interface MyViewController : UIViewController
#property (strong, nonatomic) IBOutlet UIView *detailView;
#property (strong, nonatomic) IBOutlet UILabel *theLabel;
- (IBAction)changeLabel:(id)sender;
#end
MyViewController.m
#import "MyViewController.h"
#import "MySubViewcontroller.h"
#interface MyViewController ()
#end
#implementation MyViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
MySubViewController *subVC = [[MySubViewController alloc] init];
[self addChildViewController:subVC];
[self.detailView addSubview:subVC.view];
// [subVC setDelegate:self]; (no success trying this)
[subVC didMoveToParentViewController:self];
}
-(void)viewWillAppear:(BOOL)animated
{
MySubViewController *mySubVC = [[MySubViewController alloc] init];
[mySubVC setDelegate:self];
[mySubVC doSomeTask]; // this works fine
}
// delegate method
- (void)changeLabel{
self.theLabel.text = #"Hello!";
}
MySubviewController.h
#import <UIKit/UIKit.h>
#protocol MySubViewControllerDelegate <NSObject>
#required
- (void)changeLabel;
#end
#interface MySubViewController : UIViewController
#property (nonatomic, assign) id delegate;
- (IBAction)changeButton:(id)sender;
- (void)doSomeTask;
- (void)goChangeLabel;
#end
MySubViewController.m
#import "MySubViewController.h"
#interface MySubViewController ()
#end
#implementation MySubViewController
#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)goChangeLabel
{
[[self delegate] changeLabel];
}
- (void)doSomeTask
{
[NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:#selector(goChangeLabel) userInfo:nil repeats:NO];
}
- (IBAction)changeButton:(id)sender {
// [self doSomeTask]; (no succes trying this)
}
#end

Answer 1

Your problem is this:
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
MySubViewController *subVC = [[MySubViewController alloc] init];
[self addChildViewController:subVC];
[self.detailView addSubview:subVC.view];
// [subVC setDelegate:self]; (no success trying this)
[subVC didMoveToParentViewController:self];
}
-(void)viewWillAppear:(BOOL)animated
{
MySubViewController *mySubVC = [[MySubViewController alloc] init];
[mySubVC setDelegate:self];
[mySubVC doSomeTask]; // this works fine
}
In these 2 methods you have created 2 separate variables of type MySubViewController. You have only set the delegate on the variable created inside viewWillAppear.
These are not static classes, singletons or anything else similar. If you create a variable of one type it is in no way linked to the other. The same way you can create multiple NSString's that have no bearing on each other.
Create it like so:
#implementation MyViewController
{
MySubViewController *_subVC;
}
- (void)viewDidLoad
{
[super viewDidLoad];
_subVC = [[MySubViewController alloc] init];
}
now you can use _subVC everywhere in that file as the one reference