FsAdventJp_Activity1.cs

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace FsAndroid1
{
    [Activity(Label = "FsAndroid1", MainLauncher = true, Icon = "@drawable/icon")]
    public class Activity1 : Activity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            // Get our button from the layout resource,
            // and attach an event to it
            Button button = FindViewById<Button>(Resource.Id.MyButton);

            button.Click += (_, __) => button.Text = new FsAndroid.Library.Class1().X;
        }
    }
}