为什么LongListSelector不显示，绑定的数据也不显示，请高手请教？

xaml代码：

 <phone:PhoneApplicationPage.Resources>    

    <DataTemplate x:Name="itemTemplate">      

    <StackPanel>              

 <TextBlock Text="{Binding Height}"/>

<TextBlockText="{Binding Weight}" />           

 <TextBlock Text="{Binding Sex}" />      

   </StackPanel>          

</DataTemplate>      

   <DataTemplate x:Name="headTemplate">   

   <StackPanel>               

            <TextBlock  Text="{Binding Name}" />       

    </StackPanel>    

     </DataTemplate>  

   </phone:PhoneApplicationPage.Resources>

 
<Grid x:Name="ContentPanel">
            <phone:LongListSelector 
                Visibility="Visible"  
                Name="myLongListSelector"
                ItemTemplate="{StaticResource itemTemplate}"
                GroupHeaderTemplate="{StaticResource headTemplate}"
                LayoutMode="List"
                 IsGroupingEnabled="True"
                HideEmptyGroups="True"
                /> 

 cs代码：

public class person
        {
            public string Name { get; set; }
            public string Height { get; set; }
            public string Weight { get; set; }
            public string Sex { get; set; }
        }
        private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
        {
            List<person> list = new List<person>();
            list.Add(new person() {Name="sdf",Height="23",Weight="34",Sex="nan" });
            list.Add(new person() { Name = "aa", Height = "11", Weight = "22", Sex = "nan" });
            list.Add(new person() { Name = "ss", Height = "22", Weight = "43", Sex = "nv" });
            list.Add(new person() { Name = "dd", Height = "44", Weight = "56", Sex = "nan" });
            list.Add(new person() { Name = "ff", Height = "55", Weight = "65", Sex = "nv" });
            list.Add(new person() { Name = "dd", Height = "66", Weight = "87", Sex = "nan" });
            myLongListSelector.ItemsSource = list;
        }