wpf中，xml绑定到datacontext和绑定到普通object 有何区别？

1.XML如下:

代码

   
     

    
      
    
      <
    
      Root
    
      >
    
       
 
    
      <
    
      Unions
    
      >
    
      
 
    
      <
    
      Item 
    
      FURN_GRP_ID
    
      ="64"
    
       FURN_GRP_NAME
    
      ="ddd"
    
       
    
      />
    
      
 
    
      <
    
      Item 
    
      FURN_GRP_ID
    
      ="61"
    
       FURN_GRP_NAME
    
      ="沿海地"
    
       
    
      />
    
      
 
    
      <
    
      Item 
    
      FURN_GRP_ID
    
      ="62"
    
       FURN_GRP_NAME
    
      ="地中海"
    
       
    
      />
    
      
 
    
      <
    
      Item 
    
      FURN_GRP_ID
    
      ="63"
    
       FURN_GRP_NAME
    
      ="沙滩"
    
       
    
      />
    
      
 
    
      </
    
      Unions
    
      >
    
      

    
      </
    
      Root
    
      >
    
      

   
     

 

 

 

2. Xaml里面这样子绑定
<XmlDataProvider x:Key="typeData" Source="Xml/Base.xml" XPath="/Root" />

3.把指定的节点绑定到DataContext和Test
<UC:UCUnionList Grid.Column="3" Margin="27,0,83,10" x:Name="ucUnionList"
                                 DataContext="{Binding Source={StaticResource typeData},XPath=/Root/Unions/Item}"
                                 Test="{Binding Source={StaticResource typeData},XPath=/Root/Unions/Item}"
                                 />

 

4.UCUnionList的cs里面这样写：

代码

   
     

    
      
    
      [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
[Localizability(LocalizationCategory.NeverLocalize)]
public object Test

    
      {
    
      
 get { return GetValue(TestProperty); 
    
      }
    
      
 set 
    
      {
    
       SetValue(TestProperty, value); 
    
      }
    
      
}

public static readonly DependencyProperty TestProperty = DependencyProperty.Register("Test",
 typeof(object), typeof(UCUnionList));


   
     

 

 

5.在cs代码里面检测拿到的值

var a = ucUnionList.Test;
var b = ucUnionList.DataContext;

发现这个情况
a.GetType()
{Name = "XmlElement" FullName = "System.Xml.XmlElement"}
只拿到了一个子节点，即  <Item FURN_GRP_ID="64" FURN_GRP_NAME="ddd" />

b.GetType()
{Name = "XmlDataCollection" FullName = "MS.Internal.Data.XmlDataCollection"}
拿到了所有的子节点
 <Item FURN_GRP_ID="64" FURN_GRP_NAME="ddd" />
<Item FURN_GRP_ID="61" FURN_GRP_NAME="沿海地" />
<Item FURN_GRP_ID="62" FURN_GRP_NAME="地中海" />
<Item FURN_GRP_ID="63" FURN_GRP_NAME="沙滩" />

 

求教各位，这是为什么呢？