Why isn't my UILabel being set?

Question

I have 2 view controllers. viewController1 has a UILabel called nameLabel which I want to set in a different class, viewController2.

I try calling this code from viewController2.

Content1ViewController *viewController1 = [Content1ViewController new];
    viewController1.nameLabel.text = @"HELLO";

    NSLog(@"%@",viewController1.nameLabel);

However, the viewController1 nameLabel doesn't change when I call the code? Also the NSLog returns "null"?? Can someone tell me why this is happening and also how I can change the nameLabel from a different class? Thanks!

Answer 1

Controls are not initialized when you manually create the instance. This is done on a later stage of view controller life cycle.

If I'm not mistaken, first event where you will see controls initialized is viewDidLoad

Something you can do is adding a NSString property named (let's say) nameLabelText and do nameLabel.text = nameLabelText; on viewDidLoad

Answer 2

You need to take the same instance of viewController which was on the window. If you are pushing viewController2 into navigation controller stack then get instance of viewController1 from navigation stack and then try to set the label.

If you are using present modal then use presentingViewController instance of viewController2 in order to access instance of viewController1 like

viewController1 *controller = [viewController2 presentingViewController];
[controller.nameLabel setText:@"WhatEver"];

Answer 3

Where have you set the property for namelabel? Did you use Interface Builder (XIB or Storyboard) or have you done it all in code? If the you did it in InterfaceBuilder than

 [Content1ViewController new]

is the wrong approach. For XIB-Files you should use

initWithNibName:(NSString *)nibName
                     bundle:(NSBundle *)nibBundle

and if your ViewController has been defined in a storyboard you should use

instantiateViewControllerWithIdentifier:(NSString *)identifier

from UIStoryboard.

But as Claudio Redi already said the earliest point where you will be able to access the UILabel will be in viewDidLoad

If everything in code, you should put

[self setNameLabel:[[UILabel alloc] initWithFrame:CGRectMake(50.0f,50.0f,100.0f,100.0f)];

in the init-Method of your ViewController.

Answer 4

//
//  ViewController.m
//  UIPageViewControllerDemo
//
//  Created by YunYi1118 on 15/5/20.
//  Copyright (c) 2015年 Xiaoyi. All rights reserved.
//

#import "ViewController.h"
#import "MoreViewController.h"

@interface ViewController () <UIPageViewControllerDataSource, UIPageViewControllerDelegate>

@property (strong, nonatomic) UIPageViewController *pageController;

@property (strong, nonatomic) NSArray *pageContent;

@end

@implementation ViewController

@synthesize pageContent = _pageContent;
@synthesize pageController = _pageController;

- (void)viewDidLoad {
    [super viewDidLoad];
    [self createContentPages];
    NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithInteger:UIPageViewControllerSpineLocationMin] forKey:UIPageViewControllerOptionSpineLocationKey];

    self.pageController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:options];

    _pageController.dataSource = self;
    _pageController.view.frame = self.view.bounds;

    MoreViewController *initialViewController = [self viewControllerAtIndex:0];
    NSArray *viewControllers = [NSArray arrayWithObject:initialViewController];
    [self.pageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
    [self addChildViewController:_pageController];
    [self.view addSubview:_pageController.view];


}

- (MoreViewController *)viewControllerAtIndex:(NSUInteger)index
{
    if (self.pageContent.count == 0 || index >= self.pageContent.count) {
        return nil;
    }
    MoreViewController *dataViewController = [[MoreViewController alloc] init];
    dataViewController.dataObject = [self.pageContent objectAtIndex:index];
    return dataViewController;
}

- (void)createContentPages
{
    NSMutableArray *pageStrings = [NSMutableArray array];
    for (int i = 1; i < 11; i++) {
        NSString *contentString = [[NSString alloc] initWithFormat:@"Chapter%d, This is the page %d of content displayed using UIPageViewController ",i,i];
        [pageStrings addObject:contentString];
    }
    self.pageContent = [NSArray arrayWithArray:pageStrings];
}

#pragma mark - delegate

- (NSUInteger)indexOfViewController:(MoreViewController *)viewController
{
    return [self.pageContent indexOfObject:viewController.dataObject];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    NSUInteger index = [self indexOfViewController:(MoreViewController *)viewController];
    if (index == 0 || index == NSNotFound) {
        return nil;
    }
    index--;
    return [self viewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
    NSUInteger index = [self indexOfViewController:(MoreViewController *)viewController];
    if (index == NSNotFound) {
        return nil;
    }
    index++;
    if (index == self.pageContent.count) {
        return nil;
    }
    return [self viewControllerAtIndex:index];
}

@end