error when using waitActivityIndicator, how to solve?

I am making a connection via web api in my application, so it is not accepting the use of "waitActivityIndicator", indicates that it does not exist in the current context, below my code, could someone tell me how to solve this:

using EbsHelpDesk.Models;
using EbsHelpDesk.Services;
using EbsHelpDesk.Views;
using Newtonsoft.Json;
using System;
using System.Collections.ObjectModel;
using System.Net.Http;
using Xamarin.Forms;

namespace EbsHelpDesk.Views
{
    public partial class LoginPage : TabbedPage
    {

        public LoginPage()
        {
            InitializeComponent();
            NavigationPage.SetHasNavigationBar(this, false);

        }

        protected async void BtnLogin_Clicked(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(emailEntry.Text))
            {
                await DisplayAlert("Erro", "Digite um nome de usuário válido", "Aceitar");
                emailEntry.Focus();
                return;
            }
            if (string.IsNullOrEmpty(senhaEntry.Text))
            {
                await DisplayAlert("Erro", "Digite uma senha", "Aceitar");
                emailEntry.Focus();
                return;
            }
            this.logar();


            App.Current.MainPage = new MainPageRoot();
        }

        private async void logar()
        {
            waitActivityIndicator.IsRunning = true;
            var loginRequest = new LoginRequest
            {
                Usuario = emailEntry.Text,
                Senha = senhaEntry.Text,
            };
            var JsonRequest = JsonConvert.SerializeObject(loginRequest);
            var httpContent = new StringContent(JsonRequest);
            var resp = string.Empty;

            try
            {
                var client = new HttpClient();
                client.BaseAddress = new Uri("http://ativoproject.ebasesistemas.com.br");
                var url = "/login";
                var result = await client.PostAsync(url, httpContent);

                if (!result.IsSuccessStatusCode)
                {
                    await DisplayAlert("Erro", "Usuario ou senha incorretos", "Aceitar");
                    waitActivityIndicator.IsRunning = false;
                    return;
                }

                resp = await result.Content.ReadAsStringAsync();
            }
            catch (Exception ex)
            {
                await DisplayAlert("Erro", ex.Message, "Aceitar");
                waitActivityIndicator.IsRunning = false;
                return;

            }

            var user = JsonConvert.DeserializeObject<UserName>(resp);
            waitActivityIndicator.IsRunning = false;
            await DisplayAlert("Bem vindo","vc esta logado", "Aceitar");
        }
    }
}