问按代码选择TextCell不会突出显示行

EN

using MyApp.Model;
using System.Collections.Generic;
using Xamarin.Forms;

namespace MyApp
{
    public class IntSelector : ContentPage
    {
        private ListView m_ListView;

        public IntSelector(int uSelectedInt)
        {
            DataTemplate nTemplate = new DataTemplate(typeof(TextCell));

            // We can set data bindings to our supplied objects.
            nTemplate.SetBinding(TextCell.TextProperty, "String");
            nTemplate.SetBinding(TextCell.DetailProperty, "Int");

            List<clsStringInt> nList = new List<clsStringInt>();

            clsStringInt nItem1 = new clsStringInt { String = "German", Int = 1031 };
            clsStringInt nItem2 = new clsStringInt { String = "English", Int = 1033 };
            clsStringInt nItem3 = new clsStringInt { String = "Spanish", Int = 1034 };

            nList.Add(nItem1);
            nList.Add(nItem2);
            nList.Add(nItem3);

            m_ListView = new ListView();
            m_ListView.ItemTemplate = nTemplate;
            m_ListView.ItemsSource = nList;

            m_ListView.ItemSelected += this.OnSelection;

            m_ListView.SelectedItem = nItem2;//this triggers the "OnSelection" event, so it works
            nItem2.String = "->> " + nItem2.String; //the item's new string is display in the ListView, so that works as well
            //what DOESN'T work is the highliting

            this.Content = m_ListView;
        }

        void OnSelection(object sender, SelectedItemChangedEventArgs e)
        {
            if (e.SelectedItem == null)
            {
                return; //ItemSelected is called on deselection, which results in SelectedItem being set to null
            }

            clsStringInt n = (clsStringInt)e.SelectedItem;
            string sSelectedIntAsString = n.Int.ToString();

            DisplayAlert("Item Selected", sSelectedIntAsString, "Ok");
        }

    }
}

namespace MyApp.Model
{
    public class clsStringInt
    {
        public string String { get; set; }
        public int Int { get; set; }
    }
}