MainActivity.cs

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

namespace AutoComplete
{
    [Activity(Label = "AutoComplete", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        AutoCompleteTextView autocomplete1;
        Button btn_Submit;


        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);
            autocomplete1 = FindViewById<AutoCompleteTextView>(Resource.Id.autoComplete1);
            btn_Submit = FindViewById<Button>(Resource.Id.btn_Submit);
            var kota = new string[] { "Makassar", "Balikpapan", "Jakarta", "Jogja", "Surabaya", "Ambon", "Medan" };
            ArrayAdapter adapter = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleSpinnerItem, kota);
            autocomplete1.Adapter = adapter;

            btn_Submit.Click += Btn_Submit_Click;

        }

        private void Btn_Submit_Click(object sender, EventArgs e)
        {
            if (autocomplete1.Text!="")
            {
                Toast.MakeText(this, "Kota dimasukkan =" + autocomplete1.Text, ToastLength.Short).Show();
            }
            else
            {
                Toast.MakeText(this, "silahkan masukan nama kota dulu", ToastLength.Short).Show();
            }
        }
    }
}