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POawakeFromNib, outlets and storyboards: is the documentation wrong?
 

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  1. POawakeFromNib, outlets and storyboards: is the documentation wrong?
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    <p>According to the <a href="http://developer.apple.com/library/ios/#documentation/UIKit/Reference/NSObject_UIKitAdditions/Introduction/Introduction.html" rel="nofollow noreferrer">NSObject UIKit Additions Reference</a>, outlet variables should be set by the time <code>awakeFromNib</code> is called (emphasis all mine):</p> <blockquote> <p>The nib-loading infrastructure sends an awakeFromNib message to each object recreated from a nib archive, but only after all the objects in the archive have been loaded and initialized. <strong>When an object receives an awakeFromNib message, it is guaranteed to have all its outlet and action connections already established.</strong></p> <p>...</p> <p>Important: Because the order in which objects are instantiated from an archive is not guaranteed, your initialization methods should not send messages to other objects in the hierarchy. <strong>Messages to other objects can be sent safely from within an awakeFromNib method.</strong></p> <p>Typically, you implement awakeFromNib for objects that require additional set up that cannot be done at design time. For example, you might use this method to customize the default configuration of any controls to match user preferences or the values in other controls. You might also use it to restore individual controls to some previous state of your application.</p> </blockquote> <p>However, this does not match my tests, at least using Storyboards. The results of the following test seem to contradict the documentation:</p> <ul> <li>Create a new Single View Application in Xcode.</li> <li>Drag a second ViewController onto the storyboard.</li> <li>Give the first ViewController a button, and create a modal segue from that button that displays the second ViewController.</li> <li>Create a ViewController class file for the second ViewController.</li> <li>Create a label on the second ViewController on the storyboard and create an outlet called <code>someLabel</code> from it to the corresponding ViewController class.</li> <li>Add the following <code>awakeFromNib</code> implementation to the second ViewController:</li> </ul> <p>.</p> <pre><code>- (void) awakeFromNib { [super awakeFromNib]; if (self.someLabel == nil) { NSLog(@"someLabel property is nil"); } else { NSLog(@"someLabel property is not nil"); } if (_someLabel == nil) { NSLog(@"_someLabel is nil"); } else { NSLog(@"_someLabel is not nil"); } } </code></pre> <ul> <li>Run the app in the simulator and click the button.</li> </ul> <p>When I do this, I observe the following logged:</p> <pre><code>2013-07-01 09:24:35.755 test[498:c07] someLabel property is nil 2013-07-01 09:24:35.758 test[498:c07] _someLabel is nil </code></pre> <p>As a consequence of this behaviour, when I need my ViewControllers to have some initialisation logic that involves their outlets, I need to use a hack like the one proposed in the answer <a href="https://stackoverflow.com/questions/1935526/make-a-view-initialized-from-initwithnibname-load-all-its-subview">here</a> in order to be able to use the outlets. If I'm understanding the documentation correctly, the fact that I'm forced to use this hack is a bug in the UIKit behaviour, and I <em>ought</em> to be able to put that initialisation in <code>awakeFromNib</code> and simply use the outlets without any hacks.</p> <p>I can't find any other mention of this issue on the internet, though, which seems odd given what a fundamentally important bit of functionality this appears (to me) to be. I've also never used actual nib files, only storyboards, so I'm missing some perspective on this, and the documentation on this stuff is verbose and difficult enough that as a newbie to iOS I'm not confident that I've understood correctly. Is this a genuine UIKit bug, or have I misunderstood the documentation in some way - perhaps this method isn't even meant to be used in conjunction with storyboards?</p>
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    1. USMark Amery
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    1. COGot it. This applies to `nib` files indeed, but _not_ storyboards.
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      1. POawakeFromNib, outlets and storyboards: is the documentation wrong?
      1. USAlladinian
    2. CO@Alladinian Does the documentation say this, or is this what you observe from testing? If it's in the docs, what do they say about when `awakeFromNib` gets called for ViewControllers loaded from Storyboards and what guarantees exist at the time that it's called, and where is this documentation located? If it's from testing, perhaps provide a little extra detail - as an answer if necessary? In any case, thanks for the info.
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      1. USMark Amery
    3. COHi Mark. The documentation doesn't say anything about Storyboards (in `awakeFromNib`), all this information applies to nibs. I have also tested it. Now the only thing kept me from posting this as an answer is that I cannot find any relevant documentation that _explicitly_ makes a note on this behavior.
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