Bug 21253 - Cannot retrieve .Net object from BaseAdapter unless it implements IJavaObject
Summary: Cannot retrieve .Net object from BaseAdapter unless it implements IJavaObject
Alias: None
Product: Android
Classification: Xamarin
Component: BCL Class Libraries ()
Version: 4.12.4
Hardware: PC Windows
: Normal normal
Target Milestone: ---
Assignee: Jonathan Pryor
Depends on:
Reported: 2014-07-10 19:11 UTC by David Schwegler
Modified: 2017-06-28 16:43 UTC (History)
5 users (show)

Is this bug a regression?: ---
Last known good build:

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Description David Schwegler 2014-07-10 19:11:44 UTC

BaseAdapter<T>'s GetItem is implemented as taking the .net object and wrapping it in a Java object (which is fine):
    public override Java.Lang.Object GetItem(int position)
      return JavaObjectExtensions.JavaCast<Java.Lang.Object>(JavaConvert.ToJavaObject<T>(this[position]));

However, the only exposed way to un-wrap this object is via JavaCast. However, that requires that the return type be an IJavaObject: 
    public static TResult JavaCast<TResult>(this IJavaObject instance) where TResult : class, IJavaObject


I have an object that actually is a .net object, and does not implement IJavaObject. However, it was originally obtained via GetItem and thus wrapped into an Java Object. I have no access to the original adapter at this point of the code.

Therefore, I have no way to convert this Java Object back to my .net object, short of doing manual reflection. (JavaConvert.FromJavaObject<> would work, but it is marked as internal.)
Comment 1 Sadik Ali 2014-11-03 04:29:58 UTC
I have checked the definition of BaseAdapter<T> and Javacast.

Screencast regarding same:

I’ll need confirmation from the developer if this is a bug. 

Leaving as NEW for now.
Comment 2 Jonathan Pryor 2014-11-03 12:24:03 UTC
To some extent, the problem is that Java.Lang.Object exists as parameter or return types at all; see Bug #6085.  That won't be fixed anytime soon.

In the meantime, how are you getting the internal wrapper? Ideally, you shouldn't know that it's there...which clearly isn't happening. Adding some public "unwrap" method also isn't ideal, as then you'd need to know it exists so that you can manually unwrap instances, which just seems like a different kind of pain.

I'd like to better understand your usage scenario, so I can see if there's a better way to support it.
Comment 3 Jon Douglas [MSFT] 2017-06-28 16:43:06 UTC
I am closing this bug due to a lack of response requested by https://bugzilla.xamarin.com/show_bug.cgi?id=21253#c2 

Please feel free to reopen this bug once you can add sufficient information.