How to write a custom initializer that prevents viewDidLoad being called?

Question

I would like to build a custom init method for a UIViewController, but after digging around on the Internet and specifically in SO I am confused about designated initializers.

I have a subclass of an UIViewController with these two initializers:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
  self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
  if ( self ) {

  }
  return self;
}

- (id) initWithFilename:(NSString *)aFilename {
  self = [self initWithNibName:@"WallpaperDetailsViewController" bundle:nil];
  if ( self ) { 
    self.filename = aFilename;
  }
  return self;
}

Then I have a viewDidLoad method that customizes the view according to the filename property:

- (void)viewDidLoad {
  [super viewDidLoad];

  // Create a UIImageView to display the wallpaper
  self.wallpaper = [[UIImageView alloc] initWithImage:[UIImage imageNamed:self.filename]];
  // ...
}

In another UIViewController I make the following call:

WallpaperDetailsViewController *detailsViewController = [[WallpaperDetailsViewController alloc] initWithFilename:@"foobar.png"];
[[self navigationController] pushViewController:detailsViewController animated:YES];

The result is that viewDidLoad is being called as a consequence of [self initWithNibName:], which does not initialize the UIImageView because self.filename is null.

According to other SO questions and answers, that should be the expected behavior. I am not sure about this because of my own experience in other projects prior to iOS 5. My question is:

How can I ensure that viewDidLoad: is call after initWithFilename: and not between initWithFilename: and initWithNibNameOrNil:bundle:?

If that's not possible, how can I implement an initializer method that receives custom data to create and customize the view?

Thanks!

Answer 1

I have found the problem.

WallpaperDetailsViewController does not inherit directly from UIViewController, but from another custom UIViewController I have implemented.

And what was the problem? That I have initialized a subview in the parent's initWithNibName method, instead of following the lazy-load technique and doing it in viewDidLoad. When WallpaperDetailsViewController was calling its parent initializer it got messy and cause viewDidLoad not to behave properly.

The solution? I moved every subview initialization in the parent class to its viewDidLoad method, and keep my original implementation of WallpaperDetailsViewController intact. Now everything is working as expected

Thanks to @Josh Caswell and @logancautrell

Answer 2

You don't need that empty implementation of initWithNibName:bundle:. Furthermore, it looks like your class here is establishing its designated initializer to be initWithFilename: If that's true, initWithFilename: should be calling the superclass's D.I.:

- (id) initWithFilename:(NSString *)aFilename {
  // Call super's designated initializer
  self = [super initWithNibName:@"WallpaperDetailsViewController" 
                         bundle:nil];
  if ( self ) { 
    self.filename = aFilename;
  }
  return self;
}

The rule is that all initializers within a class should call the class's D.I., and the D.I. should itself call the superclass's D.I.

It's not completely clear from what you've posted why loadView: is being called before your initializer has completed. Logancautrell's comment suggesting setting breakpoints in the view loading methods is good.

Answer 3

Why don't you just use a custom setter for the filename property that initializes the UIImage every time the filename is set?

Or, alternately, set the UIImage from the filename property in viewWillAppear: instead of viewDidLoad.

Answer 4

First, it is not recommended that you use dot syntax within your initializer. See the following for some good discussion:

Objective-C Dot Syntax and Init

Second, what you could do is assign the image in your initializer as well. So you could do something along the lines of

- (id) initWithFilename:(NSString *)aFilename {
   self = [self initWithNibName:@"WallpaperDetailsViewController" bundle:nil];
   if ( self ) { 
      filename = [aFilename retain];
      wallpaper = [[UIImageView alloc] initWithImage:[UIImage imageNamed:aFileName]];
   }
   return self;
}

This will allow you to get everything setup and in good shape before viewDidLoad is called.

Good Luck!