New instance of a UIViewController within another UIViewController: Why can't I set an instance variable?

Question

So I have a UIViewController subclass called MyTabBarViewController that has a UIScrollView. Inside of MyTabBarViewController I'm creating an instance of another UIViewController subclass called PhotoViewController. (Note: I'm doing this so I can set up the IBOutlets using IB)

I'm trying to set the label of each PhotoViewController instance from my TabBarViewController. And I init with nib for each PhotoViewController so I was under the impression that each PhotoViewController instance would be wired up to their respective IBOutlets - allowing me to simply set the label name using pvc.label.text = @"text I want".

Could you explain why my logic is incorrect? Because it's not working and not really sure what to do. :-/

MyTabBarViewController.m

#import "MyTabBarViewController.h"


@implementation MyTabBarViewController
@synthesize pageControl,scroller;

-(IBAction)clickPageControl:(id)sender
{
    int page=pageControl.currentPage;
    CGRect frame=scroller.frame;
    frame.origin.x = frame.size.width * page;
    frame.origin.y = 0;
    [scroller scrollRectToVisible:frame animated:YES];
}

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    int page = scrollView.contentOffset.x/scrollView.frame.size.width;
    pageControl.currentPage=page;
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)dealloc
{
    [super dealloc];
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    scroller.delegate=self;
    scroller.pagingEnabled=YES;
    scroller.directionalLockEnabled=YES;
    scroller.showsHorizontalScrollIndicator=NO;
    scroller.showsVerticalScrollIndicator=NO;
    scroller.contentSize=CGSizeMake(pageControl.numberOfPages*scroller.frame.size.width, scroller.frame.size.height);
    CGFloat scrollWidth = 0;
    int pageNumber = 0;
    for (int i=0; i<3; i++)
    {
        PhotoViewController *pvc = [[PhotoViewController alloc] initWithNibName:@"PhotoViewController" bundle:nil];
        CGRect rect = scroller.frame;
        rect.size.height = scroller.frame.size.height;
        rect.size.width = scroller.frame.size.width;
        rect.origin.x = scroller.frame.origin.x + scrollWidth;
        rect.origin.y = scroller.frame.origin.y;
        pvc.label.text = [NSString stringWithFormat:@"%d", pageNumber];
        pvc.label.textColor = [UIColor redColor];
        pvc.view.frame  = rect;
        [scroller addSubview:pvc.view];
        [pvc release];
        pageNumber++;
        scrollWidth += scroller.frame.size.width;
    }
    pageControl.numberOfPages=3;
    pageControl.currentPage=0;
    [self.view addSubview:scroller];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

PhotoViewController.h is pretty straight-forward. And PhotoViewController.m is too but I've included the implementation file in the event that my problem is in there.

PhotoViewController.m

#import "PhotoViewController.h"


@implementation PhotoViewController
@synthesize label, imageView, sendButton, cancelButton;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)dealloc
{
    [super dealloc];
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

Answer 1

You cant set any view related values like this(making object and set other enteries from that view).

Because you can't set any level's value before viewDidLoad of any view controller.What you need, you need set properties of string type for labels accordingly and set their values in MyTabBarViewController then from the stack pick up the object of the MyTabBarViewController class in PhotoViewController and then access it's properties and set your labels.

For picking the view object from stack you need to use this line

MyTabBarViewController *obj = (MyTabBarViewController *)[self.navigationController.viewControllers objectAtIndex: [self.navigationController.viewControllers count]-2];

Answer 2

The IBOutlet entities don't exist until viewDidLoad, and that doesn't generally happen until you initiate a show. Therefore, in MyTabBarViewController you're addressing a label, et al, that doesn't exist. (Of course, Objective-C conveniently ignores calls on nil pointers, so it SEEMS like it all works -- just nothing happens.)

According to the spec, you can trigger loading by referring to the view property of the view controller, but I've never tried it.