ViewDidLoad method in UIViewController - when does it get called?

Question

I have a UIViewController called LaunchController that is launched in my iPhone app when the app first opens:

@interface LaunchController : UIViewController<UINavigationControllerDelegate, UIImagePickerControllerDelegate>

Then, when a button is clicked, I push another view controller:

 MainController *c = [[MainController alloc] initWithImage:image];
 [self presentModalViewController:c animated:NO];

MainController has the following constructor, which I use:

- (id)initWithImage:(UIImage *)img
{
    self = [super init];
    if (self) {
        image = img;
        NSLog(@"inited the image");
    }

    return self;
}

and then it has a viewDidLoad method as follows:

- (void)viewDidLoad
{
    NSLog(@"calling view did load");
    [super viewDidLoad];

    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
    [self.view addSubview:imageView];
    NSLog(@"displaying main controller");
}

When the program runs, I see that the constructor for MainController is called (due to the output of NSLog), however viewDidLoad never gets called, even though I am calling presentModalViewController. Why is this? Why isn't viewDidLoad being called?

Answer 1

I think it is something as followings. When you need the property of view inside UIViewController, it will be loaded with lazy manner.

- (UIView *)view 
{
   if (_view == nil) {
      [self loadView]; //< or, the view is loaded from xib, or something else.
      [self viewDidLoad];
   }

   return _view;
} 

After the view initialized, it will call viewDidLoad to inform the UIViewController.

Answer 2

You aren't loading your view controller from a xib file, and from comments you don't have anything in loadView (which is where you would create your view controller's view if you were not using a xib file).

Therefore, your view isn't being loaded, so viewDidLoad is never called.

Typically you would use initWithNibName: to initialise a new view controller, and then set the image after it (so expose the image as a property).

viewDidLoad will be called as soon as your controller's view property is accessed, that is when you display it for the first time or request it (e.g. have some code that calls c.view.