viewWillAppear is not fired

Question

I have setup a basic test app that displays a view containing a label, with no use of IB. I want to use a custom UIView subclass AND custom UIViewController subclass.

This will run as anticipated, but the MyViewController's viewWillAppear and other similar delegates do not fire.

What am I missing to make these fire? In previous projects (using IB), these would fire just fine.

Here is the complete code:

AppDelegate - loads a 'MainVC' view controller and sets it as the root controller

#import "AppDelegate.h"
#import "MainVC.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize mainVC = _mainVC;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.mainVC = [[MainVC alloc] init];
    self.window.rootViewController = self.mainVC;
    [self.window makeKeyAndVisible];
    return YES;
}

MainVC - creates a 'MyViewController' which allocates the 'MyView' (it also passes down the frame size that should be used for the view)

#import "MainVC.h"
#import "MyViewController.h"

@implementation MainVC

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        MyViewController *controller = [[MyViewController alloc] init];
        CGRect frame;
        frame.origin.x = 5;
        frame.origin.y = 5;
        frame.size.width = self.view.frame.size.width - (2 * 5);
        frame.size.height = self.view.frame.size.height - (2 * 5);
        controller.startingFrame = frame;
        [self.view addSubview:controller.view];
    }
    return self;
}

MyViewController - creates the MyView

#import "MyViewController.h"
#import "MyView.h"

@implementation MyViewController

@synthesize startingFrame;

- (void)loadView{
    self.view = [[MyView alloc] initWithFrame:startingFrame];
}

- (void)viewWillAppear:(BOOL)animated{
    NSLog(@"appearing"); //doesn't do anything
}

- (void)viewDidAppear:(BOOL)animated{
    NSLog(@"appeared"); //doesn't do anything
}

MyView

#import "MyView.h"

@implementation MyView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor whiteColor];
        label = [[UILabel alloc] initWithFrame:CGRectMake(20, 20, 150, 40)];
        [label setText:@"Label"];
        [self addSubview:label];
    }
    return self;
}

Answer 1

Your mistake: You're setting a root view controller and then adding another's view controller view on top of that. While the second view is added to the view hierarchy, its view controller remains "unwired" this way. In fact if you check on your MainViewController's parentViewController, you will notice it's nil.

Why: The viewWillAppear method will be sent only to the root view controller or to view controllers in the hierarchy of the root view controller (those that were presented using presentModalViewController:animated: or presentViewController:animated:completion:).

Solutions: to solve it you have a few options:

1. Use your view controller as the root view controller
2. Present your view controller through one of the methods mentioned above
3. Keep your code as it is and manually wire those events to child view controllers (beware of this method though, as I believe the events you mention are automatically forwarded under iOS 5 - you can easily check this out).
4. If I recall properly another way to make these event get forwarded to your view controller is to add your view controller's view to the window, rather than to the parent view.

Answer 2

There's a number of very basic things that went wrong:

• you're doing your whole setup in initWithNibNamed: for your MainViewController, yet you're creating it calling just init. So your setup will never happen
• you're implementing a second VC (MyViewController), apparently just to create myView, which you then add to your rootVCs hierarchy. Not good! Only a single VC (in your case MainViewController) should be responsible to create and manage the views in its hierarchy
• don't do VC controller setup in loadView, like you did in MyViewController. In your case it is the only way to make things work, because MyVC never actually gets fully up and running, but the approach is wrong - you're basically forcing the View Controller to set up the view, although the controller itself is never in control of anything

There's a few more things, but those are the most important ones - it appears like it would be a good idea for you to read about the whole basic concept of the Model - View - Controller concept again. Next, you should be digging through the class references for both UIViewController and UIView.

Even if you would get the results you desire at last using your current approach, it wouldn't help you in the long run, because you wouldn't learn to use the involved elements properly.

Answer 3

Methods are not invoked on a view controller inside another view controller. If developing for iOS 5 only then check out UIViewController Containment which can be used to solve this. If you want your application to be compatible with previous iOS versions you can forward method invocations to your child view controller. Personally I prefer subclassing SFContainerViewController which handles this automatically: https://github.com/krzysztofzablocki/SFContainerViewController