IBOutlets in subview are nil - ios

Question

I have a UIViewController,which is associated with custom class MAViewControllerMenu and loads right after the splash screen. In that UIViewController, I have an UIScrollView, which belongs to another class, MASlideShowView, in which the IBOutlet of the UIScrollView is defined and is connected to.
The class for the UIViewController has, among others, the field:
#property MASlideShowView* slideShow;
as a private property for the class that holds the UIScrollView inside it.
Also in the UIViewController,
- (void)viewDidLoad
{
[super viewDidLoad];
//TODO [_slideShow initializeImages];
_slideShow = [[MASlideShowView alloc] initWithModel];
_slideShow.delegate = imageViewController;
}
- (void)viewDidAppear{
[super viewDidAppear:(YES)];
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// Set up the content size of the scroll view
//HERE, self.slideShow is allocated, but all the fields it has, including the IBOutlet to the UIScrollView is still nil
CGSize pagesScrollViewSize = self.slideShow.frame.size;
_slideShow.contentSize = CGSizeMake(pagesScrollViewSize.width * self.pageViews.count, pagesScrollViewSize.height);
//Delegate
_slideShow.scrollView.delegate = self;
// Load the initial set of pages that are on screen
[_slideShow loadVisiblePages:YES page_index:0 image:_last_image_taken];
}
Note the error I saw in the comments in the above class
The MASlideShowView file looks like:
h:
#class MASlideShowView;
#protocol slideShowDelegate <NSObject>
-(void)imageViewSelected:(MASlideShowView*)slideShow image:(UIImage*)image;
#end
#interface MASlideShowView : UIScrollView
#property (nonatomic,weak) id<slideShowDelegate> delegate;//delegate to next controller to notify upon picture centered
#property (nonatomic, strong) IBOutlet UIScrollView *scrollView;
#property (nonatomic, strong) IBOutlet UIPageControl *pageControl;
#property (weak, nonatomic) IBOutlet UIButton *rotateImageButton;
#property UIImageView* centered_image_view;
- (IBAction)PageThroughPageControl;
- (IBAction)rotateImageButtonClicked;
- (id)initWithModel;
- (void)pageThroughPageControl;
- (void)addImageToSlideshow:(UIImage*)toAdd;
- (void)loadVisiblePages:(BOOL)use_page_number page_index:(NSInteger)page image:(UIImage*)image;
#end
m:
- (id)initWithModel{
[self initializeImages];
return self;
}
-(void)initializeImages{
// Set up the image you want to scroll & zoom and add it to the scroll view
self.pageViews = [NSMutableArray arrayWithObjects:nil];
NSInteger pageCount = 0;
_imageViewCount = 0;
// Set up the page control
self.pageControl.currentPage = 0;
self.pageControl.numberOfPages = pageCount;
// Set up the array to hold the views for each page
self.pageViews = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < pageCount; ++i) {
[self.pageViews addObject:[NSNull null]];
}
}
My question is simple:
How can I make the UIScrollView initialize?
I know that there's no viewDidAppear as it inherits from UIScrollView.
Thanks

Answer 1

As you are using Interface Builder, I would recommend calling initializeImages inside awakeFromNib:
An awakeFromNib message is sent to each object loaded from the
archive, but only if it can respond to the message, and only after all
the objects in the archive have been loaded and initialized. When an
object receives an awakeFromNib message, it is guaranteed to have all
its outlet instance variables set.
More details here.
Other observations:
As for your code, you have slideShow correctly set by Interface Builder when entering viewDidLoad but you're replacing that instance by assigning _slideShow = [[MASlideShowView alloc] initWithModel], which results in a completely different object.
Moreover your initWithModel doesn't look at all like a correct init method as it doesn't call any of its super's init methods. You should start with Apple's snippet by writing init in an empty line and press escape:
Again the first paragraph of the answer should be enough for your problem.

Answer 2

There's a few ways you could go about fixing this.
One way is like #HoanNguyen mentioned to use awakeFromNib. Personally I don't use this but it's a valid lifecycle event for setup.
Another option is to override initWithCoder: which is the standard initializer storyboards use
- (id)initWithCoder:(NSCoder *)aDecoder{
self = [super initWithCoder:aDecoder];
if (self) {
[self initializeImages];
}
return self;
}
You could then remove your initWithModel call and the storyboard should handle everything.