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?

You don't actually check it if the new view was initiated. Move NSLog within the if-brackets to see if the view was initiated. — dimme, Jan 16 '12 at 06:11
Do you have a nib named `MainController.xib` in your project? If you don't, you must override `-loadView` and provide an empty view. — Jason Coco, Jan 16 '12 at 06:17
Related, if you aren't using nibs :http://stackoverflow.com/questions/8876212/proper-use-of-loadview-and-viewdidload-with-uiviewcontroller-without-nibs-xibs — jrturton, Jan 16 '12 at 06:21
that link doesn't provide an answer, just another problem. and @JasonCoco, no I don't have a nib. How can I overwrite loadView such that viewDidLoad will be called — CodeGuy, Jan 16 '12 at 06:29
I'm not actually sure it's your problem, but you can just override `-loadView` and create a view and assign it to `self.view`. Are you using storyboards? — Jason Coco, Jan 16 '12 at 06:32

score 4 · Accepted Answer · answered Jan 16 '12 at 07:27

4

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.

answered Jan 16 '12 at 07:27

AechoLiu

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Please don't do this. Apple documentation specifically states that loadView and viewDidLoad should not be called directly. From `loadView`: "You should never call this method directly." – amattn Jan 17 '12 at 18:48
4

@amattn: You are right. But I just use above codes to describe when the `-viewDidLoad` called. – AechoLiu Jan 18 '12 at 00:10

score 3 · Answer 2 · answered Jan 16 '12 at 06:17

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.

That would have been useful information to include in your question. — jrturton, Jan 16 '12 at 06:33

amattn · Answer 3 · 2012-01-16T06:50:51.313

0

The reason viewDidLoad is not being called is because you aren't loading a view.

In your init method:

 self = [super init];

means that you are just creating a naked view from scratch. not loading one from a nib.

try this instead:

self = [super initWithNibName:nil bundle:nil];

If you have a xib or nib file with the same name as the view controller class it should find if. Otherwise, you can just give a nibName that works.

UPDATE:

If you are not using nib files, then the appropriate method is NOT viewDidLoad. You have to implement loadView instead of viewDidLoad.

In your specific case, just put everything that is currently in viewDidLoad into loadView.

edited Jan 16 '12 at 06:50

answered Jan 16 '12 at 06:19

amattn

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But I'm not using nib, I want to create the view programatically. – CodeGuy Jan 16 '12 at 06:22
updated. Read the documentation for UIViewController for more specifics about loadView. – amattn Jan 16 '12 at 06:44

ViewDidLoad method in UIViewController - when does it get called?

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