在initWithNibName之后调用ViewDidLoad

Question

It appears that ViewDidLoad() is sent to a ViewController only after its View is physically displayed (ie via NavigationController pushViewController), and not immediately after initWithNibName() . Is this a behavior I can rely on? I would like to get the chance to set the member variables of my view so that all the members are valid by the time ViewDidLoad() is invoked.

Answer 1

You can set up member variables and other such things in initWithNibName:bundle: .

- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)nibBundle {
    if (self = [super initWithNibName:nibName bundle:nibBundle]) {
        // set up ivars and other stuff here.
        someIvar = someValue;
    }
    return self;
}

You are correct that viewDidLoad: is only sent when the view is physically displayed, ie when it is added to some visible view (which may sometimes be never if the user does not reach that view). So it's useful to split the functionality and think about what you can do at init time and what happens at view load time.

As Marcelo Cantos notes in the comment, viewDidLoad: is generally a fine place to do all sorts of setup work, using the concept of "lazy loading," so that you defer the setup until as late time as possible.

Answer 2

viewDidLoad is called before a view controller is displayed for the first time, not immediately after initWithNibName . For example, if you have a tab bar controller, all of the child view controllers will be init d at launch, but viewDidLoad will only be called when you click on the appropriate tab the first time. It's generally a good idea to initialize memory-intensive items in viewDidLoad , so as to avoid using unnecessary memory.

Answer 3

Sorry to unearth an old thread, but this solved it for me...

-(void)viewDidLoad is only called after -(void)loadView has done its thing. In the docs for loadView:

The view controller calls this method when its view property is requested but is currently nil.

My view controller only has viewDidLoad called after its view is request by a UITabBarItem, meaning viewDidLoad is only called in the viewController once the tab bar button is pressed. I, like the OP, want viewDidLoad to be called directly after the nib is loaded, so it's contents (titles, etc) can be populated before the user clicks the tab button.

So, after calling "self = [super initWithNibName:@"nibName" bundle:nil];" in the view controller's custom initialiser, I immediately called '[self view]' afterwards. As the view is requested earlier than when it is requested by the UITabBarItem (which calls 'addSubview'), the view is initialised fully during initialisation, rather than when requested.

Hope this helps.

Answer 4

I found that if I override initiWithNibName in the view controller, the viewDidLoad method is not called. I have to call it manually [self viewDidLoad]. But if I do not override initWithNibName: viewDidLoad is called. I am working with 4 view controllers in tab bar controller. the tab bar controller is loaded from another view.