On Nov 16, 2012, at 8:28 PM, cocoa-dev-requ...@lists.apple.com wrote:
Date: Fri, 16 Nov 2012 14:14:08 -0800
From: Rick Mann rm...@latencyzero.com
Subject: Bugs with parentViewController?
I'm finding that parentViewController is nil for all the
UINavigationControllers embedded in my hierarchy (via storyboard). In my
case, they're embedded in UISplitViewControllers.
I wrote bugs about this, but I wanted to check to see if others are seeing
that, or if I've failed to do something properly.
When you have questions of this sort, one useful approach, rather than asking
others, is to test. When I say test, I mean, isolate the issue entirely from
the current project and work in a new project of utmost simplicity, so that
whatever complications or mistakes the real project introduces are not
introduced there. I am always surprised at the apparent failure of questioners
to do this, as it is such a helpful and easy technique.
So, for example, in this case, one could do as follows:
Make a new project, for iPad only, using the Master-Detail template. That gives
a UISplitViewController containing two UINavigationControllers, each containing
a view controller as its root. Now put a button in the deepest detail
controller in the storyboard, and connect its action to a method in
DetailViewController.m that goes like this:
- (IBAction)doButton:(id)sender {
UIViewController* vc = self;
while (vc) {
NSLog(@%@, vc);
vc = vc.parentViewController;
}
}
Now run the project and tap the button. Here's the sort of thing that results:
2012-11-17 06:25:46.627 X[416:c07] DetailViewController: 0x716c6a0
2012-11-17 06:25:46.639 X[416:c07] UINavigationController: 0x716c310
2012-11-17 06:25:46.640 X[416:c07] UISplitViewController: 0x7169090
Now, it is a law of logic that one counterexample is sufficient to disprove an
hypothesis. So if the hypothesis is that the parent is nil for navigation
controllers in split view controllers in general, that idea is false. It is far
more likely, therefore, that you've just hooked things together wrong, in your
storyboard or in code, in your one particular case.
Another way to approach the matter is through logical thinking. The parent view
controller chain is *crucial* to the entire workings of a modern iOS app.
Therefore it seems most improbable that its integrity would be violated, as all
sorts of things would break as a consequence. This reasoning has a somewhat
Kantian a priori ring to it, but it is certainly suggestive that one would do
better to doubt oneself rather than the framework in so vital and elementary a
matter.
m.
--
matt neuburg, phd = m...@tidbits.com, http://www.apeth.net/matt/
pantes anthropoi tou eidenai oregontai phusei
Programming iOS 5! http://shop.oreilly.com/product/0636920023562.do
RubyFrontier! http://www.apeth.com/RubyFrontierDocs/default.html
TidBITS, Mac news and reviews since 1990, http://www.tidbits.com
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