Andreas:
Thanks for the information. Now, I should kick myself for picking the name
initialize but then maybe I should complain about Apple picking all the best
names for methods.
I think I have used the -viewDidLoad method before.
phil
On Jan 10, 2011, at 9:58 AM, Andreas Grosam wrote:
>
> On Jan 10, 2011, at 4:17 PM, Phil Hystad wrote:
>
>> Is there a proper way to initialize a view controller. So far, I have been
>> doing this in the application delegate by calling calling an initialize
>> method ( i.e. [viewController initialize]) in
>> application:didFinishLaunchingWithOptions: method (prior to the view being
>> added to the window and the window made visible).
>
>
> *** Important ***
> +(void)initialize is a class method which the runtime sends to the class
> exactly once just before any of this class' method is invoked, and any of its
> super class if +initialized has not yet been invoked.
> You rarely need to override +initialize -- and you never call it yourself!
>
>
>
> But yes, there is a proper way to do initialization of a view controller
> object :) There are lots of examples of how you should do this within the
> iOS or Mac OS X documentation.
>
> Basically, when you load your view from a nib you will override these methods
> in order to initialize a view controller:
>
> -viewDidLoad
> This method is called regardless of whether the views were stored in a
> nib file or created
> programmatically. You usually override it to do additional setup after
> the view has been
> loaded from a nib.
> If you override -viewDidLoad you may want to override -viewDidUnload
> accordingly, which is the "counterpart" of -viewDidLoad.
>
>
> -awakeFormNib
> To do additional setup after the view has been loaded from a nib. You
> often can do all your setup
> in viewDidLoad, but sometimes this seems a better place. At the time
> the method is invoked,
> outlet and action connections are already established.
>
>
> In the cases where you want to create the controller's view yourself
> programmatically, you have to use
> -loadView. If you do so, you need to create the view hierarchy and assign the
> root view to the view property of the controller.
>
>
> You must not call any of these methods yourself! The framework will do this
> for you when it is appropriate.
>
>
> An example might be useful:
>
> The following code assumes you have a nib where you load the view:
>
> @interface MyViewController : UIViewController {
> IBOutlet UIView* mySpecialSubView;
> NSArray* myArray;
> }
>
> @property (retain) UIView* mySpecialSubView;
> @property (retain) NSArray* myArray;
>
> @end
>
> @implementation
> @synthesize mySpecialSubView;
> @synthesize myArray;
>
> - (void) viewDidLoad
> {
> [super viewDidLoad]; // always invoke super!
>
> // In debug mode, you might check here whether you have established the
> links for your outlets in IB:
> NSAssert(mySpecialSubView, @"IBOutlet 'mySpecialSubView' is nil"); //
> forgot to setup the link in IB?
>
> // configure my view unless this is already done in IB:
> self.view.backgroundColor = [UIColor blackColor];
>
> // do other setup, for instance setting up a navigation bar, navigation
> item
> ...
>
> // if your view controller needs to initialize other ivars, you might
> initialize them here,
> // or do "lazy initialization" (see below)
> ...
>
> // Note, that viewDidLoad will be called *everytime* the view gets
> reloaded from
> // the resource!
> // Sometimes, you explicitly DON'T want to perform certain initialization
> steps again
> // after the view will be reloaded. In this case, use a flag as an ivar
> which determines
> // whether you have done these initialization steps:
> if (!isInitialized) {
> [self setupOnce];
> isInitialized = YES; // this is an ivar
> }
> }
>
>
> You have to override -viewDidUnload in certain cases, e.g.:
>
> - (void) viewDidUnload {
> self.mySpecialSubView = nil; // Outlets shall be set to nil!
>
> // optionally, you might want to release myArray - just in order to safe
> memory. But
> // this depends on your needs, and often you explicitly don't want the
> array to be
> // recreated after a reload of the view.
> self.myArray = nil; // optionally
> }
>
>
>
> // lazy initialization - this overrides the getter method which was otherwise
> defined
> // by the @synthesize directive:
> - (NSArray*) myArray {
> if (myArray == nil) {
> myArray = [NSArray alloc] init... ];
> }
> return myArray;
> }
>
>
> // don't forget to release ivars if required:
> -(void) dealloc {
> [mySpecialSubView release], mySpecialSubView = nil;
> [myArray release], myArray = nil;
> [super dealloc]; // always invoke super (at the last statement)
> }
>
>
>
> One thing you should care of:
> -viewDidLoad and -awakeFormNib, as well as -loadView may be called more than
> once for the lifetime of the view controller. So, be carefully not to
> initialize ivars in such a way that you get a memory leak. The following code
> snippet would be the wrong way:
>
> - (void) viewDidLoad {
> [super viewDidLoad];
> myArray = [[NSArray alloc] init...]; // possibly memory leak!
> }
>
> The way to do proper initialization would leverage properties:
> - (void) viewDidLoad {
> [super viewDidLoad];
> NSArray* tmp = [[NSArray alloc] init...];
> self.myArray = tmp; // property retains
> [tmp release], tmp = nil;
> }
>
> However, when the view is reloaded (once it has been unloaded for some
> reason), the array will be initialized again! This may or may not have
> undesired side effects since the array will be released and initialized
> again. So, lazy initialization may be the preferred way for certain ivars.
>
>
>
> Regards,
>
> Andreas
>
>
>>
>> However, I am not sure if this is the Cocoa canonical way of doing things.
>> By the way, this example comes from UIKit but the same question would apply
>> to any OS X Cocoa application too.
>>
>> phil
>> [email protected]
>>
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