wpf listView 始终显示最新五条

  public partial class MainWindow : Window    {        ObservableCollection<Class1> items = new ObservableCollection<Class1>();        public MainWindow()        {            InitializeComponent();                        #region 定时器事件            Timer aTimer = new Timer();            aTimer.Elapsed += new ElapsedEventHandler(TimedEvent);            aTimer.Interval = 1000;    //配置文件中配置的秒数            aTimer.Enabled = true;            #endregion        }        private void TimedEvent(object source, ElapsedEventArgs e)        {            this.Dispatcher.BeginInvoke((Action)delegate()                {                    Class1 cl = new Class1();                    cl.date = DateTime.Now.ToLocalTime().ToString();                    items.Add(cl);                    listView.ItemsSource = items.OrderByDescending(t => t.date).Take(5);                });        }        public class Class1 : DependencyObject        {            public string date            {                get { return (string)GetValue(dateProperty); }                set { SetValue(dateProperty, value); }            }            // Using a DependencyProperty as the backing store for date.  This enables animation, styling, binding, etc...            public static readonly DependencyProperty dateProperty =                DependencyProperty.Register("date", typeof(string), typeof(Class1), null);        }    }

  <ListView  ScrollViewer.VerticalScrollBarVisibility="Hidden"  x:Name="listView" DataContext="{Binding}"  SelectionMode="Extended">            <ListView.View>                <GridView>                    <GridViewColumn Header="时间" Width="150"                                              DisplayMemberBinding="{Binding date,Mode=OneWay}" />                                   </GridView>            </ListView.View>        </ListView>