Svick對他的回答是正確的。您發現Elements的原因是XElement的自定義CustomTypeDescriptor（由XElement中TypeDescriptionProviderAttribute的存在確定）提供了一個名稱元素的自定義PropertyDescriptor，該元素返回IEnumerable <XElement>。如果在索引器的綁定路徑中遵循這一點，那麼返回的是XContainer.Elements（XName），否則將是XContainer.Elements（）。爲什麼Attributes不起作用是因爲沒有提供這樣的動態屬性描述符。
下面的代碼以類似於動態Elements屬性的方式提供了這個缺失的功能（還有一個Nodes屬性）。
//Add this code in App start up
TypeDescriptor.AddProvider(new XElementAdditionalDynamicPropertiesTypeDescriptionProvider(),
typeof(XElement));
下面的類提供了功能，此代碼類似於元素的工作方式。
public class XDeferredAxis : IEnumerable<XAttribute>
{
internal XElement element;
private Func<XElement, XName, IEnumerable<XAttribute>> func;
private XName name;
public IEnumerator<XAttribute> GetEnumerator()
{
return this.func(this.element, this.name).GetEnumerator();
}
public XDeferredAxis(Func<XElement, XName, IEnumerable<XAttribute>> func, XElement element, XName name)
{
if (func == null)
{
throw new ArgumentNullException("func");
}
if (element == null)
{
throw new ArgumentNullException("element");
}
this.func = func;
this.element = element;
this.name = name;
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
}
public class XElementNodesPropertyDescriptor : PropertyDescriptor
{
private XElement element;
private bool childRemoved;
public XElementNodesPropertyDescriptor() : base("Nodes", null)
{
}
public override void AddValueChanged(object component, EventHandler handler)
{
bool flag = base.GetValueChangedHandler(component) != null;
base.AddValueChanged(component, handler);
if (!flag)
{
XElement local = component as XElement;
if ((local != null) && (base.GetValueChangedHandler(component) != null))
{
element = local;
local.Changing += new EventHandler<XObjectChangeEventArgs>(this.OnChanging);
local.Changed += new EventHandler<XObjectChangeEventArgs>(this.OnChanged);
}
}
}
private void OnChanging(object sender, XObjectChangeEventArgs e)
{
childRemoved = false;
if (e.ObjectChange == XObjectChange.Remove)
{
XObject senderNode = (XObject)sender;
if (senderNode.Parent == element)
{
childRemoved = true;
}
}
}
private void OnChanged(object sender, XObjectChangeEventArgs e)
{
XObject senderNode = (XObject)sender;
switch (e.ObjectChange)
{
case XObjectChange.Add:
case XObjectChange.Value:
case XObjectChange.Name:
if (senderNode.Parent == element)
{
this.OnValueChanged(element, EventArgs.Empty);
}
break;
case XObjectChange.Remove:
if (childRemoved)
{
this.OnValueChanged(element, EventArgs.Empty);
}
break;
}
}
public override void RemoveValueChanged(object component, EventHandler handler)
{
base.RemoveValueChanged(component, handler);
XElement local = component as XElement;
if ((local != null) && (base.GetValueChangedHandler(component) == null))
{
local.Changed -= new EventHandler<XObjectChangeEventArgs>(this.OnChanged);
}
}
public override bool SupportsChangeEvents
{
get
{
return true;
}
}
public override Type ComponentType
{
get
{
return typeof(XElement);
}
}
public override bool IsReadOnly
{
get
{
return true;
}
}
public override Type PropertyType
{
get
{
return typeof(IEnumerable<XNode>);
}
}
public override bool CanResetValue(object component)
{
return false;
}
public override object GetValue(object component)
{
var nodes= (component as XElement).Nodes();
return nodes;
}
public override void ResetValue(object component)
{
}
public override void SetValue(object component, object value)
{
}
public override bool ShouldSerializeValue(object component)
{
return false;
}
}
public class XElementAttributesPropertyDescriptor : PropertyDescriptor
{
private XDeferredAxis value;
private bool removalIsOwnAttribute;
public XElementAttributesPropertyDescriptor() : base("Attributes", null) {
}
public override void AddValueChanged(object component, EventHandler handler)
{
bool flag = base.GetValueChangedHandler(component) != null;
base.AddValueChanged(component, handler);
if (!flag)
{
XElement local = component as XElement;
if ((local != null) && (base.GetValueChangedHandler(component) != null))
{
local.Changing += new EventHandler<XObjectChangeEventArgs>(this.OnChanging);
local.Changed += new EventHandler<XObjectChangeEventArgs>(this.OnChanged);
}
}
}
private void OnChanging(object sender, XObjectChangeEventArgs e)
{
removalIsOwnAttribute = false;
if (e.ObjectChange == XObjectChange.Remove)
{
var xAttribute = sender as XAttribute;
if (xAttribute != null && xAttribute.Parent == value.element)
{
removalIsOwnAttribute = true;
}
}
}
private void OnChanged(object sender, XObjectChangeEventArgs e)
{
var changeRequired = false;
var xAttribute = sender as XAttribute;
if (xAttribute != null)
{
switch (e.ObjectChange)
{
case XObjectChange.Name:
case XObjectChange.Add:
if (xAttribute.Parent == value.element)
{
changeRequired = true;
}
break;
case XObjectChange.Remove:
changeRequired = removalIsOwnAttribute;
break;
}
if (changeRequired)
{
this.OnValueChanged(value.element, EventArgs.Empty);
}
}
}
public override void RemoveValueChanged(object component, EventHandler handler)
{
base.RemoveValueChanged(component, handler);
XElement local = component as XElement;
if ((local != null) && (base.GetValueChangedHandler(component) == null))
{
local.Changed -= new EventHandler<XObjectChangeEventArgs>(this.OnChanged);
}
}
public override bool SupportsChangeEvents
{
get
{
return true;
}
}
public override Type ComponentType
{
get
{
return typeof(XElement);
}
}
public override bool IsReadOnly
{
get
{
return true;
}
}
public override Type PropertyType
{
get
{
return typeof(IEnumerable<XAttribute>);
}
}
public override bool CanResetValue(object component)
{
return false;
}
public override object GetValue(object component)
{
return (object)(this.value = new XDeferredAxis((Func<XElement, XName, IEnumerable<XAttribute>>)((e, n) =>
{
if (!(n != (XName)null))
return e.Attributes();
return e.Attributes(n);
}), component as XElement, (XName)null));
}
public override void ResetValue(object component)
{
}
public override void SetValue(object component, object value)
{
}
public override bool ShouldSerializeValue(object component)
{
return false;
}
}
public class XElementAdditionalDynamicPropertiesTypeDescriptionProvider: TypeDescriptionProvider
{
public XElementAdditionalDynamicPropertiesTypeDescriptionProvider() : this(TypeDescriptor.GetProvider(typeof(XElement))) { }
protected XElementAdditionalDynamicPropertiesTypeDescriptionProvider(TypeDescriptionProvider parent) : base(parent) { }
public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
{
var baseTypeDescriptor= base.GetTypeDescriptor(objectType, instance);
return new XElementAdditionalDynamicPropertiesTypeDescriptor(baseTypeDescriptor);
}
}
public class XElementAdditionalDynamicPropertiesTypeDescriptor : CustomTypeDescriptor
{
public XElementAdditionalDynamicPropertiesTypeDescriptor(ICustomTypeDescriptor original) : base(original) { }
public override PropertyDescriptorCollection GetProperties()
{
return GetProperties(null);
}
public override PropertyDescriptorCollection GetProperties(Attribute[] attributes)
{
PropertyDescriptorCollection descriptors = new PropertyDescriptorCollection(null);
if (attributes == null)
{
descriptors.Add(new XElementAttributesPropertyDescriptor());
descriptors.Add(new XElementNodesPropertyDescriptor());
}
foreach (PropertyDescriptor pd in base.GetProperties(attributes))
{
descriptors.Add(pd);
}
return descriptors;
}
}
謝謝你，這是我的問題的正確答案。再次感謝！ – 2012-02-29 23:53:30