iPhone SDK: what is the difference between loadView and viewDidLoad?

Question

When working with views and view controllers in an iPhone app, can anyone explain the difference between loadView and viewDidLoad?

My personal context, is that I build all my views from code, I do not and will not use Interface Builder, should that make any difference.

I've found that often when I add init code to loadView, I end up with an infinite stack trace, so I typically do all my child-view building in viewDidLoad...but it's really unclear to me when each gets executed, and what is the more appropriate place to put init code. What would be perfect, is a simple diagram of the initialization calls.

Thanks!

Solution 1

I can guess what might be the problem here, because I've done it:

I've found that often when I add init code to loadView, I end up with an infinite stack trace

Don't read self.view in -loadView. Only set it, don't get it.

The self.view property accessor calls -loadView if the view isn't currently loaded. There's your infinite recursion.

The usual way to build the view programmatically in -loadView, as demonstrated in Apple's pre-Interface-Builder examples, is more like this:

UIView *view = [[UIView alloc] init...];
...
[view addSubview:whatever];
[view addSubview:whatever2];
...
self.view = view;
[view release];

And I don't blame you for not using IB. I've stuck with this method for all of Instapaper and find myself much more comfortable with it than dealing with IB's complexities, interface quirks, and unexpected behind-the-scenes behavior.

Solution 2

loadView is the method in UIViewController that will actually load up the view and assign it to the view property. This is also the location that a subclass of UIViewController would override if you wanted to programatically set up the view property.

viewDidLoad is the method that is called once the view has been loaded. This is called after loadView is called. It is a place where you can override and insert code that does further initial setup of the view once it has been loaded.

Solution 3

viewDidLoad()

is to be used when you load your view from a NIB and want to perform any customization after launch

LoadView()

is to be used when you want to create your view programmatically (without the use of Interface Builder)

Solution 4

Just adding some code examples to demonstrate what NilObject said:

- (void)loadView
{
    // create and configure the table view
    myTableView = [[UITableView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame] style:UITableViewStyleGrouped];   
    myTableView.delegate = self;
    myTableView.dataSource = self;
    myTableView.scrollEnabled = NO;
    self.view = myTableView;

    self.view.autoresizesSubviews = YES;
}

- (void)viewDidLoad 
{
  self.title = @"Create group";

  // Right menu bar button is to Save
  UIBarButtonItem *saveButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Save" style:UIBarButtonItemStyleDone target:self action:@selector(save)];
  self.navigationItem.rightBarButtonItem = saveButtonItem;
  [saveButtonItem release];
}

Solution 5

To prevent an infinite loop from happening when you read self.view, call the class' super implementation when you load a view. The super implementation will allocate a new UIView for you.

- (void) loadView {
[super loadview];

// init code here...

[self.view addSubView:mySubview1]; //etc..

}

View more solutions

Comments

[ryan.scott]

so, between the two of you, is it accurate to say that loadView is where I should do the alloc/init of my controller's self.view, and child views should be handled in viewDidLoad (or later)?

[ryan.scott]

ahhhh, thank you for an explanation, finally! I've shied away from the idiom of allocating a temporary variable, then setting to self.view, then releasing...it seemed somehow awkward, unnecessary. I can now understand why that decision would have led me down the path where I now find myself.

[Ivan Vučica]

I could swear Apple's documentation said you should not call [super loadView];. That was contradicted in the examples, but I think the docs said it correctly (I have found numerous bugs in examples over time). [super loadView] is needed for UITableViewController etc, though. However! Any post-load setup (e.g. adding extra subviews) should be done in viewDidLoad.

[futureelite7]

I have called [super loadView] without any side effects so far. It may be true if you intend to set self.view to something you made yourself though.

[Ian1971]

If you call [super loadView] inside loadView then it will attempt to load the view from a nib if available with default name. So you need to be careful.

[user2054339]

I have such code and there is no recursion. why? -(void) loadView { // Frame for Hypnosis view CGRect frame = [[UIScreen mainScreen] bounds]; // Create a Hipnosis view v = [[HypnosisView alloc] initWithFrame:frame]; self.view = v;

[Alex Nazarov]

And if you call [super loadView], you initialize self.view in super loadView method

[ruandao]

This may have some problem, I have test when my view controller was not associate with NIB file, viewDidLoad still called