-viewDidLoad未在子类UIViewController中调用

Question

Have patience with me, I'm still learning Cocoa Touch. Other -viewDidLoad not being called question was unrelated to my issue, I did search.

I have FooViewController , a UIViewController subclass. FooViewController.xib has its File's Owner set to FooViewController. Additionally, I have Main , whose App Delegate is MyApplication and whose File's Owner is UIApplication . My primary nib is set to Main.

I am able to make the view appear on the screen, using this flow (code snipped for brevity):

UIWindow *main;

-(void)applicationDidFinishLaunching:(UIApplication*)application {
    [self showFooViewController];
    [main makeKeyAndVisible];
}

-(void)showFooViewController {
    fooViewController = [[FooViewController alloc] init];
    if(![[NSBundle mainBundle] loadNibNamed:@"FooViewController" owner:fooViewController options:nil]) {
        DebugF(@"Failed to load FooViewController");
        return;
    }

    // Add the view and put it in place
    UIView *view = [fooViewController view];
    CGRect cur = [view frame];
    cur.origin = CGPointMake(0.0f, 20.0f);
    [view setFrame:cur];

    [main addSubview:[fooViewController view]];
}

However, this message is not being sent to FooViewController :

- (void) viewDidLoad {
    DebugF(@"Hello!");
}

Total silence in gdb's output.

I've seen other Cocoa tutorials that show Instances and such in IB's document view, but I do not see these options in mine. Am I supposed to be instantiating fooViewController in the Nib? Did I miss a connection? In FooViewController.xib, File's Owner view is connected to the view in the Nib.

I'm sure this is a simple solution, and I have wandered down the wrong path. Halp!

Answer 1

I have not found documentation to back up the following, but this is what I've deduced by experiment / experience:

The viewDidLoad method is expected be called immediately after loadView is called, and it's up to whomever calls loadView to supply the extra call to viewDidLoad .

In some cases, the SDK will handle this behavior for you. Suppose you have a subclass of UIViewController called MyViewController ; then:

• If you access myViewController.view before you call loadView , then the superclass accessor is smart enough to call loadView for you, and viewDidLoad immediately thereafter.

As a result, if your code looks like this:

MyViewController *myViewController = [[MyViewController alloc] init];
[superView addSubview:myViewController.view];  // Calls viewDidLoad.

then both loadView and viewDidLoad will be called on your behalf.

However, if your code looks like this:

MyViewController *myViewController = [[MyViewController alloc] init];
[myViewController loadView];
[superView addSubview:myViewController.view];  // Doesn't call viewDidLoad.

then the view getter can see you've already loaded the view, and it assumes you also called viewDidLoad as well - so it doesn't call either. Ironically, the extra function call here prevents viewDidLoad from getting called.

Answer 2

I have had this same problem twice. The first time, I forgot to connect the view of UITableViewController to the actual UITableView in interface builder. The second time, I forgot to make awakeFromNib call itself in the superclass.

Answer 3

And I've answered my own question, so this may help future folks. Since I see viewDidLoad has, as its three top Googles in my suggest, "viewDidLoad not called", "viewDidLoad not getting called", and "viewDidLoad not firing", I imagine this is a usual mistake...

Changing:

fooViewController = [[FooViewController alloc] init];
if(![[NSBundle mainBundle] loadNibNamed:@"FooViewController" owner:fooViewController options:nil]) {
    DebugF(@"Failed to load FooViewController");
    return;
}

To:

fooViewController = [[FooViewController alloc] initWithNibName:@"FooViewController" bundle:[NSBundle mainBundle]];

Fixed the problem. Obviously a mistake in how I'm using Cocoa.