LoginActivity.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Newtonsoft.Json.Linq;

namespace PariwisataJateng
{
    [Activity(Label = "Login",Theme = "@style/Temaku")]
    public class LoginActivity : Activity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.Login);

            EditText txtEmail = FindViewById<EditText>(Resource.Id.txtEmail);
            EditText txtPassword = FindViewById<EditText>(Resource.Id.txtPassword);
            Button btnLogin = FindViewById<Button>(Resource.Id.btnLogin);
            Button btnDaftar = FindViewById<Button>(Resource.Id.btnDaftar);

            btnDaftar.Click += delegate {
                StartActivity(typeof(DaftarActivity));
            };

            btnLogin.Click += delegate {
                string email = txtEmail.Text;
                string password = txtPassword.Text;

                WebClient webclient = new WebClient();
                var jsonstring = webclient.DownloadString("https://banyu.center/pariwisatajateng/api/login_member?email=" + email + "&password=" + password + "&id_level=3");
                JObject o = JObject.Parse(jsonstring);
                var ab = o.GetValue("login_event").ToString();
                //JArray arr = JArray.Parse(ab);

                if (string.IsNullOrWhiteSpace(ab))
                {
                    Toast.MakeText(this, "Email dan Password Salah", ToastLength.Short).Show();
                }
                else
                {
                    Toast.MakeText(this, "Login Berhasil", ToastLength.Short).Show();
                    StartActivity(typeof(MainActivity));
                }


            };

            // Create your application here
        }
    }
}