好的，我相信我已经通过使用操作行为来修改底层消息，然后再通过 IDispatchMessageFormatter 对其进行格式化。
以下代码针对基于 WCF 无文件激活的服务提供了解决方案。
我想让我的 IOperationBehavior 以 Attribute 类的形式存在。然后我可以简单地用我的新属性装饰每个服务操作，这将激发该操作的 IOperationBehavior - 对最终用户来说非常好和简单。
关键问题是你在哪里应用行为，这很关键。通过属性应用行为时，WCF 调用的操作行为的顺序与在服务主机应用时不同。基于属性的顺序如下：
- System.ServiceModel.Dispatcher.OperationInvokerBehavior
- MyOperationBehaviorAttribute
- System.ServiceModel.OperationBehaviorAttribute
- System.ServiceModel.Description.DataContractSerializerOperationBehavior
- System.ServiceModel.Description.DataContractSerializerOperationGenerator
由于某种原因，操作行为（仅当通过使用属性应用时）将在 DataContractSerializerOperationBehavior 之前调用。这是一个问题，因为在我的行为中，在我调整了消息（参见代码）之后，我想将反序列化委托给我的格式化程序中的 DataContractSerializerOperationBehavior 格式化程序（作为内部格式化程序传递给我的行为）。当微软已经提供了一个非常好的反序列化器时，我不想重新编写反序列化例程。我只是在第一个实例中更正 XML，以便将空白转换为在 XML 中正确表示的空值，以便 DataContractSerializer 可以将它们绑定到服务接口中的可为空类型。
所以这意味着我们不能按预期使用基于属性的行为，因为 WCF 很可能在这里以一种相当微妙的方式被破坏，因为我看不出这种现象的原因。所以我们仍然可以在操作中添加一个 IOperationBehavior，我们只需要在服务主机创建阶段手动分配它，因为然后我们的 IOperationBehavior 被插入到“正确”的序列中，即在创建 DataContractSerializerOperationBehavior 之后，只有这样我可以参考内部格式化程序吗？
// This operation behaviour changes the formatter for a specific set of operations in a web service.
[System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple = false)]
public class NullifyEmptyElementsAttribute : Attribute
{
// just a marker, does nothing
}
public class NullifyEmptyElementsBahavior : IOperationBehavior
{
#region IOperationBehavior Members
public void AddBindingParameters(OperationDescription operationDescription, System.ServiceModel.Channels.BindingParameterCollection bindingParameters)
{
}
public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation) { }
public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
{
// we are the server, we need to accept client message that omit the xsi:nill on empty elements
dispatchOperation.Formatter = new NullifyEmptyElementsFormatter(dispatchOperation.Formatter);
}
public void Validate(OperationDescription operationDescription) { }
#endregion IOperationBehavior Members
}
/// <summary>
/// This customized formatter intercepts the deserialization process to perform extra processing.
/// </summary>
public class NullifyEmptyElementsFormatter : IDispatchMessageFormatter
{
// Hold on to the original formatter so we can use it to return values for method calls we don't need.
private IDispatchMessageFormatter _innerFormatter;
public NullifyEmptyElementsFormatter(IDispatchMessageFormatter innerFormatter)
{
// Save the original formatter
_innerFormatter = innerFormatter;
}
/// <summary>
/// Check each node and add the xsi{namespace}:nil declaration if the inner text is blank
/// </summary>
public static void MakeNillable(XElement element)
{
XName _nillableAttributeName = "{http://www.w3.org/2001/XMLSchema-instance}nil"; // don't worry, the namespace is what matters, not the alias, it will work
if (!element.HasElements) // only end nodes
{
var hasNillableAttribute = element.Attribute(_nillableAttributeName) != null;
if (string.IsNullOrEmpty(element.Value))
{
if (!hasNillableAttribute)
element.Add(new XAttribute(_nillableAttributeName, true));
}
else
{
if (hasNillableAttribute)
element.Attribute(_nillableAttributeName).Remove();
}
}
}
public void DeserializeRequest(System.ServiceModel.Channels.Message message, object[] parameters)
{
var buffer = message.CreateBufferedCopy(int.MaxValue);
var messageSource = buffer.CreateMessage(); // don't affect the underlying stream
XDocument doc = null;
using (var messageReader = messageSource.GetReaderAtBodyContents())
{
doc = XDocument.Parse(messageReader.ReadOuterXml()); // few issues with encoding here (strange bytes at start of string), this technique resolves that
}
foreach (var element in doc.Descendants())
{
MakeNillable(element);
}
// create a new message with our corrected XML
var messageTarget = Message.CreateMessage(messageSource.Version, null, doc.CreateReader());
messageTarget.Headers.CopyHeadersFrom(messageSource.Headers);
// now delegate the work to the inner formatter against our modified message, its the parameters were after
_innerFormatter.DeserializeRequest(messageTarget, parameters);
}
public System.ServiceModel.Channels.Message SerializeReply(System.ServiceModel.Channels.MessageVersion messageVersion, object[] parameters, object result)
{
// Just delegate this to the inner formatter, we don't want to do anything with this.
return _innerFormatter.SerializeReply(messageVersion, parameters, result);
}
}
public class MyServiceHost : ServiceHost
{
public MyServiceHost(Type serviceType, params Uri[] baseAddresses)
: base(serviceType, baseAddresses) { }
protected override void OnOpening()
{
base.OnOpening();
foreach (var endpoint in this.Description.Endpoints)
{
foreach (var operation in endpoint.Contract.Operations)
{
if ((operation.BeginMethod != null && operation.BeginMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0)
||
(operation.SyncMethod != null && operation.SyncMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0)
||
(operation.EndMethod != null && operation.EndMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0))
{
operation.Behaviors.Add(new NullifyEmptyElementsBahavior());
}
}
}
}
}
也许因为我只是修改传入的消息，我可以改为使用 IDispatchMessageInspector，这将消除对 IDispatchMessageFormatter 激活顺序的依赖。但这暂时有效；）
用法：
- 添加到您的操作中
[ServiceContract(Namespace = Namespaces.MyNamespace)]
public interface IMyServiceContrct
{
[OperationContract]
[NullifyEmptyElements]
void MyDoSomthingMethod(string someIneteger);
}
- 融入您的服务
A.如果您有 .svc，只需引用 MyServiceHost
<%@ ServiceHost
Language="C#"
Debug="true"
Service="MyNameSpace.MyService"
Factory="MyNameSpace.MyServiceHost" %>
B.如果您使用无文件激活服务，请将其添加到您的 web.config 文件中
<system.serviceModel>
... stuff
<serviceHostingEnvironment multipleSiteBindingsEnabled="true" >
<!-- WCF File-less service activation - there is no need to use .svc files anymore, WAS in IIS7 creates a host dynamically - less config needed-->
<serviceActivations >
<!-- Full access to Internal services -->
<add relativeAddress="MyService.svc"
service="MyNameSpace.MyService"
factory="MyNameSpace.MyServiceHost" />
</serviceActivations>
</serviceHostingEnvironment>
... stuff
</system.serviceModel>