NotifyDataSetChanged not working

for example list has rows with ages

On searching 45 you get the result filtered as 45. but clicking on it results on showing age from 1. it is like the position does not change for the ages but uses the original ArrayList adapter position.

my code is as below,

  public class MainActivity : Activity
    {
        private List<Friend> mFriends;
        private ListView mListView;
        private EditText mSearch;
        private LinearLayout mContainer;
        private bool mAnimatedDown;
        private bool mIsAnimating;
        private FriendsAdapter mAdapter;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);
            mListView = FindViewById<ListView>(Resource.Id.listView);
            mSearch = FindViewById<EditText>(Resource.Id.etSearch);
            mContainer = FindViewById<LinearLayout>(Resource.Id.llContainer);

            mSearch.Alpha = 0;
            mSearch.TextChanged += mSearch_TextChanged;

            mFriends = new List<Friend>();
            mFriends.Add(new Friend { FirstName = "Bob", LastName = "Smith", Age = "33", Gender = "Male" });
            mFriends.Add(new Friend { FirstName = "Tom", LastName = "Smith", Age = "45", Gender = "Male" });
            mFriends.Add(new Friend { FirstName = "Julie", LastName = "Smith", Age = "2020", Gender = "Unknown" });
            mFriends.Add(new Friend { FirstName = "Molly", LastName = "Smith", Age = "21", Gender = "Female" });
            mFriends.Add(new Friend { FirstName = "Joe", LastName = "Lopez", Age = "22", Gender = "Male" });
            mFriends.Add(new Friend { FirstName = "Ruth", LastName = "White", Age = "81", Gender = "Female" });
            mFriends.Add(new Friend { FirstName = "Sally", LastName = "Johnson", Age = "54", Gender = "Female" });

            mAdapter = new FriendsAdapter(this, Resource.Layout.row_friend, mFriends);
            mListView.Adapter = mAdapter;


            mListView.ItemClick += MListView_ItemClick;
        }

        private void MListView_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
        {
            var friend = mFriends[e.Position];


            Toast.MakeText(this, friend.Age, ToastLength.Short).Show();
        }

        void mSearch_TextChanged(object sender, Android.Text.TextChangedEventArgs e)
        {

            List<Friend> searchedFriends = (from friend in mFriends
                                            where friend.FirstName.Contains(mSearch.Text, StringComparison.OrdinalIgnoreCase) || friend.LastName.Contains(mSearch.Text, StringComparison.OrdinalIgnoreCase)
                                            || friend.Age.Contains(mSearch.Text, StringComparison.OrdinalIgnoreCase) || friend.Gender.Contains(mSearch.Text, StringComparison.OrdinalIgnoreCase)
                                            select friend).ToList<Friend>();

            mAdapter = new FriendsAdapter(this, Resource.Layout.row_friend, searchedFriends);
            mListView.Adapter = mAdapter;
            mAdapter.NotifyDataSetChanged();


        }

im working this examples
http://cforbeginners.com/XamarinProjects.html >>Xamarin 15 - Searching a Listview using LINQ