async void onAddBtnClicked(object sender, EventArgs e)
 {
     var nextPage = new CategoriasCreateUpdatePage(rubricaUid, true)
     {
         BindingContext = new Categoria()
     };
     await Navigation.PushAsync(nextPage);
 }
        async public void OnEdit(object sender, EventArgs e)
        {
            var       menuItem  = ((MenuItem)sender);
            Categoria categoria = menuItem.CommandParameter as Categoria;

            var nextPage = new CategoriasCreateUpdatePage(rubricaUid, false)
            {
                BindingContext = categoria
            };
            await Navigation.PushAsync(nextPage);
        }