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PODoes UIViewController's presentModalViewController:animated: retain the modal controller?
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copied!<p>This has implications on the way I interact with my modal controllers. When I first started out in iOS development, I assumed that <code>UIViewController</code> <em>did not</em> retain the modally presented view. Well, really it was more like I had no reason to assume it <em>did</em> retain them. This left me with fairly awkward attempts at releasing them when I knew they would have finished their dismissal animations:</p> <pre><code>_myViewController = [[UIViewController alloc] init]; [self. present modalViewController:_myViewController animated:YES]; /* Some stuff, then in a different method all together, probably as the result of a delegate callback or something... */ [self dismissModalViewControllerAnimiated:YES]; [_myViewController performSelector:@selector(release) withObject:nil afterDelay:0.5f]; </code></pre> <p>Then, I saw the <code>modalViewController</code> property of <code>UIViewController</code> and thought, "Man, I hope it retains that property when a modal view controller is presented." Sure enough, I logged the retain count on several of these attempts and noticed a general increase immediate after the call to <code>presentModalViewController:animated:</code> (I know, retain counts are not a perfect metric). So, somewhere along the line, I have started using a much nicer pattern where I assume that any controller object I present modally is retained by the presenting controller. This lets me write the standard present code:</p> <pre><code>UIViewController* myViewController = [[UIViewController alloc] init]; [self presentModalViewController:myViewController animated:YES]; [myViewController release]; // <- Fire and forget! </code></pre> <p>Now, of course, there is no awkwardness: no need to wait for an animation to finish, or even keep a reference to the presented controller if I don't need it. I can blindly dismiss it later and not worry about leaking. I like it.</p> <p>I have logged many a dealloc in my modally presented controllers and they are always called precisely when I want, which leads me to feel confident in my approach: <code>UIViewController</code>'s <code>presentModalViewController:animated:</code> retains the presented controller as the <code>modalViewController</code> property.</p> <p>But, and this is the meat of this question, I realized that I can't confirm this as <strong><em>documented</em></strong> behavior. And if it's not documented, I should not feel nearly as safe as I do, because Apple makes no promises about the longevity of undocumented behavior. The <code>modalViewController</code> property is publicly <code>readonly</code>, so I can only assume a retain behind the scenes, and the documentation on <code>presentModalViewController:animated:</code> says only:</p> <blockquote> <p>Sets the modalViewController property to the specified view controller.</p> </blockquote> <p>"Sets" could be <code>assign</code> or <code>retain</code>. Nothing I read blatantly confirms or denies my position. Since this is an assumption I make often, I would really love it if someone could point out a fact that I have missed somewhere in the bowels of documentation to put my mind at ease about the legitimacy of this practice.</p> <p><strong>EDIT:</strong> In the ebb and flow of day-to-day life in the iOS SDK, I found myself in the header for UIViewController and started reading some of it. I gleaned some useful info that reminded me of this question and I decided to post it, in the event some future user stumbles upon this question and wants as much info as possible to satisfy their paranoia of a very standard practice. The little morsel is simply this, from the @interface ivar block in UIViewController.h:</p> <pre><code>UIViewController *_childModalViewController; </code></pre> <p>As opposed to these other declarations:</p> <pre><code>UIViewController *_parentViewController; // Nonretained NSHashTable *_childViewControllers; // Nonretained </code></pre> <p>The comments seem to explicitly state what is <em>not</em> retained. By virtue of a lack of comment on the modal view controller ivar declaration, it would seem it <em>is</em> retained.</p>

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