private async void btnLog_Clicked(object sender, EventArgs e)
 {
     if (BoolChecks.AdminLogged)
     {
         await Navigation.PushAsync(new AdminPage());
     }
     else
     {
         AdminLogin adminList = new AdminLogin();
         BookAdmin  bookAdmin = new BookAdmin();
         adminList.BindingContext = bookAdmin;
         await Navigation.PushAsync(adminList);
     }
 }
        private async void Button_Clicked(object sender, EventArgs e)
        {
            BookAdmin admin = new BookAdmin();

            if (entryLog.Text == admin.Login && entryPass.Text == admin.Password)
            {
                BoolChecks.AdminLogged = true;
                await Navigation.PushAsync(new AdminPage());
            }
            else
            {
                await DisplayAlert("Error", "Incorrect login or password", "OK");
            }
        }