IPolicyImportExtension.ImportPolicy 方法

定义

命名空间:

System.ServiceModel.Description

程序集:

System.ServiceModel.dll

定义一个可导入自定义策略断言和添加实现绑定元素的方法。

public:
 void ImportPolicy(System::ServiceModel::Description::MetadataImporter ^ importer, System::ServiceModel::Description::PolicyConversionContext ^ context);

public void ImportPolicy (System.ServiceModel.Description.MetadataImporter importer, System.ServiceModel.Description.PolicyConversionContext context);

abstract member ImportPolicy : System.ServiceModel.Description.MetadataImporter * System.ServiceModel.Description.PolicyConversionContext -> unit

Public Sub ImportPolicy (importer As MetadataImporter, context As PolicyConversionContext)

参数

importer

MetadataImporter

正在使用的 MetadataImporter 对象。

context

PolicyConversionContext

PolicyConversionContext，其中既包含可以导入的策略断言，也包含可向其添加实现绑定元素的绑定元素集合。

示例

下面的代码示例演示了如何使用 PolicyAssertionCollection.Remove 方法在一个步骤内完成断言的查找、返回和移除操作。

  #region IPolicyImporter Members
  public const string name1 = "acme";
  public const string ns1 = "http://Microsoft/WCF/Documentation/CustomPolicyAssertions";

  /*
   * Importing policy assertions usually means modifying the bindingelement stack in some way
   * to support the policy assertion. The procedure is:
   * 1. Find the custom assertion to import.
   * 2. Insert a supporting custom bindingelement or modify the current binding element collection
   *     to support the assertion.
   * 3. Remove the assertion from the collection. Once the ImportPolicy method has returned,
   *     any remaining assertions for the binding cause the binding to fail import and not be
   *     constructed.
   */
  public void ImportPolicy(MetadataImporter importer, PolicyConversionContext context)
  {
    Console.WriteLine("The custom policy importer has been called.");
    // Locate the custom assertion and remove it.
    XmlElement customAssertion = context.GetBindingAssertions().Remove(name1, ns1);
    if (customAssertion != null)
    {
      Console.WriteLine(
        "Removed our custom assertion from the imported "
        + "assertions collection and inserting our custom binding element."
      );
      // Here we would add the binding modification that implemented the policy.
      // This sample does not do this.
      Console.ForegroundColor = ConsoleColor.Red;
      Console.WriteLine(customAssertion.NamespaceURI + " : " + customAssertion.Name);
      Console.WriteLine(customAssertion.OuterXml);
      Console.ForegroundColor = ConsoleColor.Gray;
    }
 }
#endregion

    #Region "IPolicyImporter Members"
    Public Const name1 As String = "acme"
    Public Const ns1 As String = "http://Microsoft/WCF/Documentation/CustomPolicyAssertions"

'    
'     * Importing policy assertions usually means modifying the bindingelement stack in some way
'     * to support the policy assertion. The procedure is:
'     * 1. Find the custom assertion to import.
'     * 2. Insert a supporting custom bindingelement or modify the current binding element collection
'     *     to support the assertion.
'     * 3. Remove the assertion from the collection. Once the ImportPolicy method has returned, 
'     *     any remaining assertions for the binding cause the binding to fail import and not be 
'     *     constructed.
'     
    Public Sub ImportPolicy(ByVal importer As MetadataImporter, ByVal context As PolicyConversionContext) Implements IPolicyImportExtension.ImportPolicy
      Console.WriteLine("The custom policy importer has been called.")
      ' Locate the custom assertion and remove it.
      Dim customAssertion As XmlElement = context.GetBindingAssertions().Remove(name1, ns1)
      If customAssertion IsNot Nothing Then
        Console.WriteLine("Removed our custom assertion from the imported " & "assertions collection and inserting our custom binding element.")
        ' Here we would add the binding modification that implemented the policy.
        ' This sample does not do this.
        Console.ForegroundColor = ConsoleColor.Red
        Console.WriteLine(customAssertion.NamespaceURI & " : " & customAssertion.Name)
        Console.WriteLine(customAssertion.OuterXml)
        Console.ForegroundColor = ConsoleColor.Gray
      End If
    End Sub
  #End Region

下面的代码示例演示了客户端应用程序配置文件是如何在调用 System.ServiceModel.Description.MetadataResolver 时加载自定义策略导入程序的。

<client>
    <endpoint 
      address="http://localhost:8080/StatefulService" 
      binding="wsHttpBinding"
      bindingConfiguration="CustomBinding_IStatefulService" 
      contract="IStatefulService"
      name="CustomBinding_IStatefulService" />
  <metadata>
    <policyImporters>
      <extension type="Microsoft.WCF.Documentation.CustomPolicyImporter, PolicyExtensions"/>
    </policyImporters>
  </metadata>
</client>

下面的代码示例演示了如何使用 MetadataResolver 下载元数据，并将其解析到说明对象中。

// Download all metadata.
ServiceEndpointCollection endpoints
  = MetadataResolver.Resolve(
    typeof(IStatefulService),
    new EndpointAddress("http://localhost:8080/StatefulService/mex")
  );

' Download all metadata. 
Dim endpoints As ServiceEndpointCollection = MetadataResolver.Resolve(GetType(IStatefulService), New EndpointAddress("http://localhost:8080/StatefulService/mex"))

注解

实现 ImportPolicy 方法可以获取策略断言，并修改某些导入协定或绑定，以支持该断言。 通常，策略导入程序可通过配置绑定元素或将其插入到正在导入的绑定，来对查找自定义策略断言作出响应。

Windows Communication Foundation (WCF) 将两个 PolicyConversionContext对象传递给 ImportPolicy 方法，即 MetadataImporter 和 。 通常，PolicyConversionContext 对象包含每个绑定范围的策略断言。

IPolicyImportExtension 实现会完成以下操作步骤：

1. 调用 GetBindingAssertions、GetMessageBindingAssertions 或 GetOperationBindingAssertions 方法，依据范围查找其所负责的自定义策略断言。

2. 从断言集合中移除策略断言。 PolicyAssertionCollection.Remove 方法在一个步骤中就可以完成断言的查找、返回和移除操作。

3. 通过将所需的自定义 BindingElement 添加到 BindingElements 属性，或修改 PolicyConversionContext.Contract 属性，可以修改绑定堆栈或协定。

步骤 2 非常重要。 调用所有策略导入程序后，WCF 会检查是否存在任何策略断言。 如果存在，WCF 假定策略导入失败，并且不导入关联的绑定。