导航属性绑定Xamarin表单

Question

请帮帮我我是Xamarin表单的新手，我想绑定到ICollection（Navigation Property）的属性。我试过很多方法它没有用，例如我试过我需要这样做工作任何帮助将不胜感激。我正在使用MVVM帮助器和James Montemagno分组并使用棱镜 如何绑定到导航属性？ 感谢

  Public Class Category{
  public int ID {get;set;}
  public string CatName {get;set;}
  public virtual ICollection<Item> items {get;set;}
  }



  Public Class Item{
  public Id {get;set;}
  public Catname{get;set;}
  public ItemName {get;set;}
  Public virtual <SubItems> SubItems {get;set;}
   }
  Public Class SubItem{
  public Id {get;set;}
  public ItemName{get;set;}
  public SubItemName {get;set;}

  }
  Public Class Expandable : BaseViewMdoel{
  public Catagory CataGory{ get;set;}
  public bool IsSelected {get;set;}

  }

  Public Class ExpandableListView : BaseViewModel{
  public ObservableRangeCollection<Catagory> CollectionOfCatagory { get; } = 
  new ObservableRangeCollection<Catagory>();
  public ObservableCollection<Grouping<Expandable ,Catagory>>SelectedCatagroy
  { get; set; } = new ObservableCollection<Grouping<Expandable, Catagory>>();

  public DelegateCommand<Grouping<Expandable,Catagory>> HeaderCommand
  {get
    {
        return new DelegateCommand<Grouping<Expandable , Catagory>>(g =>
        {
            if (g == null) return;
            g.Key.IsSelected = !g.Key.IsSelected;

            if (g.Key.IsSelected )
            {
                foreach (var item in CollectionOfCatagory )
                {
                     var m = item.Catagory.Where(i => i.ID == 
                     g.Key.Catagory.ID);
                    foreach (var x in m)
                    {
                        g.Add(item);                                                  
                    } 
                }

                }
            else
            {
                g.Clear();
            }
        });
    }
}


  Void GroupListOfItem(){
 var items = CollectionOfCatagory.Select(
 x => new Expandable{ Catagory = x, IsSelected = false }
        ).GroupBy(c => new { c.Catagory.CatName}).Select(g => 
 g.First()).ToList();
 items.ForEach(c => SelectedCatagroy.Add(new 
 Grouping<Expandable, Catagory>(c, new 
 ObservableRangeCollection<Catagory>())));
 }
 }

我的观点：

   <ListView ItemsSource="{Binding CollectionOfCatagory }" 
   IsGroupingEnabled="True">

   <ListView.GroupHeaderTemplate>
    <DataTemplate>
        <ViewCell>
            <ContentView Padding="10,0,0,0">
                <Label Text="{Binding Key.Catagory.CatName}" 
            VerticalOptions="Center"/>
            <ContentView.GestureRecognizers>
                    <TapGestureRecognizer Command="{Binding Source=
             {x:Reference CatagoryListPage}, 
             Path=BindingContext.HeaderCommand}"  CommandParameter="
             {Binding .}" />
            </ContentView.GestureRecognizers>    
            </ContentView>
        </ViewCell>
    </DataTemplate>
</ListView.GroupHeaderTemplate>
<ListView.ItemTemplate>
    <DataTemplate>
        <ViewCell>
            <StackLayout  Padding="10,0,0,0">
                <StackLayout Orientation="Horizontal">
                    <StackLayout  WidthRequest="40">
                        <Label Text="{Binding Catname}" />
                    </StackLayout>
             <Label  Text = {Binding How To bind to properties of 
                             navigation Please help} 
                    </StackLayout>
                    <Image Source="Cat1"/>
                </StackLayout>
            </StackLayout>
        </ViewCell>