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POIs this a bug in MonoTouch GC?
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copied!<blockquote> <p>Note: <a href="http://dl.dropbox.com/u/76095045/MTMemoryTest.zip" rel="nofollow noreferrer">I've created a simple project</a>—you can see how switching types between <code>UIButton</code> and <code>CustomButton</code> in storyboard changes GC behavior.</p> </blockquote> <p>I'm trying to get my head wrapped around MonoTouch garbage collector.<br> The issue is similar to <a href="https://stackoverflow.com/q/4902967/458193">the one fixed in MT 4.0</a>, however with inherited types.</p> <p>To illustrate it, consider two view controllers, parent and child. </p> <p>Child's view contains a single <code>UIButton</code> that writes to console on tap.<br> Controller's <code>Dispose</code> method throws an exception so it's hard to miss.</p> <p>Here goes child view controller:</p> <pre><code>public override void ViewDidLoad () { base.ViewDidLoad (); sayHiButton.TouchUpInside += (sender, e) => SayHi(); } } void SayHi() { Console.WriteLine("Hi"); } protected override void Dispose (bool disposing) { throw new Exception("Hey! I've just been collected."); base.Dispose (disposing); } </code></pre> <p>Parent view controller just presents child controller and sets a timer to dismiss it and run GC:</p> <pre><code>public override void ViewDidLoad () { base.ViewDidLoad (); var child = (ChildViewController)Storyboard.InstantiateViewController("ChildViewController"); NSTimer.CreateScheduledTimer(2, () => { DismissViewController(false, null); GC.Collect(); }); PresentViewController(child, false, null); } </code></pre> <p>If you run this code, it predictably crashes inside <code>ChildViewController.Dispose()</code> called from its finalizer because child controller has been garbage collected. Cool.</p> <p>Now open the storyboard and change button type to <code>CustomButton</code>. MonoDevelop will generate a simple <code>UIButton</code> subclass:</p> <pre><code>[Register ("CustomButton")] public partial class CustomButton : UIButton { public CoolButton (IntPtr handle) : base (handle) { } void ReleaseDesignerOutlets() { } } </code></pre> <p>Somehow changing the button type to <code>CustomButton</code> is enough to trick garbage collector into thinking child controller is not yet eligible for collection.</p> <p>How is that so?</p>

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