Converting Java nested classes to Xamarin.Android

Question

A typical pattern in Android/Java development is to have a nested class that access methods from the parent class:

public class MainActivity extends FragmentActivity {

  // implementation

  public class SectionsPagerAdapter extends FragmentPagerAdapter {
    String someString = getString(R.string.thestring);
  }
}

So in this case, the Context.getString() would be accessing the MainActivity context.
How would this convert to Xamarin.Android (Mono for Android)?
When trying the exact same pattern I get:

Error CS0038: Cannot access a nonstatic member of outer type Test.MainActivity' via nested typeTest.MainActivity.SectionsPagerAdapter' (CS0038)

I could of course pass around a Context object, but that seems tedious to do.

I always extract nested class out and pass Activity in a constructor. — Aaron He
– Aaron He, Commented Mar 8, 2013 at 23:20
Also, could take a look at section 4.5 of docs.xamarin.com/guides/android/advanced_topics/api_design. — Aaron He
– Aaron He, Commented Mar 8, 2013 at 23:36
Hmm... that explains it. Write that down as an answer, and I'll accept it — Magnus Johansson
– Magnus Johansson, Commented Mar 9, 2013 at 0:10
Thanks. Could you do me a favor? Could you suggest tag xamarin.android is a synonym of monodroid? I can't do it because I am under 2.5k reputation. :( — Aaron He
– Aaron He, Commented Mar 9, 2013 at 0:21

Aaron He · Accepted Answer · 2013-03-09 00:19:17Z

3

According to API design document of Xamarin.Android:

Non-static nested classes, also called inner classes, are significantly different. They contain an implicit reference to an instance of their enclosing type and cannot contain static members (among other differences outside the scope of this overview).

So, you should pass a reference of MainActivity to SectionsPagerAdapter. Then, you could access members of MainActivity.

answered Mar 9, 2013 at 0:19

Aaron He

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1 Comment

Christopher Francisco Over a year ago

could you write an example please?

Daniele D. · Accepted Answer · 2015-01-21 11:25:32Z

Here an example. I hope it helps.

public class YourParentClassActivity : Activity
{
//your stuff 
//...


//The Nested Class (that can implement any interface or base class)
    class YourNextedExampleClass : WebViewClient
    {
        //Parent Class Reference
        private YourParentClassActivity _pc;
        public YourNextedExampleClass(YourParentClassActivity pc)
        {
            _pc = pc;
        }

        public override void OnReceivedSslError(WebView view, SslErrorHandler handler, SslError SSLError)
        {
            Intent i = new Intent(Intent.ActionView, Android.Net.Uri.Parse("xxx");
            _pc.StartActivity(i);
            _pc.Finish();
            handler.Proceed(); // Ignore SSL certificate errors
        }
    }

}

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