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    <p>Congratulations! You've hit a leaky abstraction. :-/</p> <p>The problem is this: <a href="https://www.securecoding.cert.org/confluence/display/java/MET05-J.+Ensure+that+constructors+do+not+call+overridable+methods" rel="noreferrer">for better or worse</a>, virtual method calls from constructors invoke the most derived method implementation. C# is the same as Java in this respect; consider the following program:</p> <pre><code>using System; class Base { public Base () { Console.WriteLine ("Base..ctor"); M (); } public virtual void M () { Console.WriteLine ("Base.M"); } } class Derived : Base { public Derived () { Console.WriteLine ("Derived..ctor"); } public override void M () { Console.WriteLine ("Derived.M"); } } static class Demo { public static void Main () { new Derived (); } } </code></pre> <p>When run, the output is:</p> <pre><code>Base..ctor Derived.M Derived..ctor </code></pre> <p>That is, the <code>Derived.M()</code> method is invoked before the <code>Derived</code> constructor has executed.</p> <p>In Mono for Android, things get more...complicated. The <a href="http://docs.xamarin.com/android/advanced_topics/architecture/android_callable_wrappers" rel="noreferrer">Android Callable Wrapper (ACW)</a>'s constructor is invoked by Java and is responsible for creating the <a href="http://docs.xamarin.com/android/advanced_topics/garbage_collection#Cross-VM_Object_Collections" rel="noreferrer">peer C# instance and mapping the Java instance to the C# instance</a>. <em>However</em>, if a virtual method is invoked from the Java constructor, then the method will be dispatched <em>before there is a C# instance to invoke the method upon!</em></p> <p>Let that sink in a bit.</p> <p>I don't know which method is triggering the scenario for your specific code (the code fragment you provided works fine), but we do have a sample which hits this scenario: <a href="https://github.com/xamarin/monodroid-samples/blob/master/ApiDemo/Text/LogTextBox.cs#L26" rel="noreferrer">LogTextBox</a> <a href="https://github.com/xamarin/monodroid-samples/blob/master/ApiDemo/Text/LogTextBox.cs#L45" rel="noreferrer">overrides</a> the <a href="http://androidapi.xamarin.com/?link=P:Android.Widget.TextView.DefaultMovementMethod" rel="noreferrer">TextView.DefaultMovementMethod</a> property, and the <a href="https://github.com/android/platform_frameworks_base/blob/gingerbread-release/core/java/android/widget/TextView.java#L366" rel="noreferrer"><code>TextView</code> constructor invokes the <code>getDefaultMovementMethod()</code> method</a>. The result is that Android tries to invoke <code>LogTextBox.DefaultMovementMethod</code> before a <code>LogTextBox</code> instance even exists.</p> <p>So what does Mono for Android do? Mono for Android created the ACW, and thus knows which C# <em>type</em> the <code>getDefaultMovementMethod()</code> method should be delegated to. What it doesn't have is an instance, because one hasn't been created. So Mono for Android creates an instance of the appropriate type...via the <code>(IntPtr, JniHandleOwnership)</code> constructor, and generates an error if this constructor cannot be found.</p> <p>Once the (in this case) <code>TextView</code> constructor finishes executing, the <code>LogTextBox</code>'s ACW constructor will execute, at which point Mono for Android will go "aha! we've already created a C# instance for this Java instance", and will <em>then</em> invoke the appropriate constructor on the already created instance. Meaning that for a single instance, two constructors will be executed: the <a href="https://github.com/xamarin/monodroid-samples/blob/master/ApiDemo/Text/LogTextBox.cs#L28" rel="noreferrer"><code>(IntPtr, JniHandleOwnership)</code> constructor</a>, and (later) the <a href="https://github.com/xamarin/monodroid-samples/blob/master/ApiDemo/Text/LogTextBox.cs#L41" rel="noreferrer"><code>(Context, IAttributeSet, int)</code> constructor</a>.</p>
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    1. COthanks a lot! That was very helpful. I need to re-read your post and let it sink in a bit, and then take a look at my code with this new knowledge and see where my problem could be. I'll post another comment when I find something out.
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    2. COI have simple code that reproduces the issue (sorry for the long amount of time it has been since the original question). Using the code sample above, simply add one method: public override void RequestLayout(). Overriding RequestLayout reproduces the issue. Also, overriding OnLayout() will reproduce it as well...but not quite as reliably (still can't figure out the exact cases under which it does).
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