为什么来自 Unity.Wcf 的服务主机无法正确解析服务实例？

Question

我有一个统一容器：

var unityContainer = new UnityContainer();

配置如下：

unityContainer.RegisterType<IExampleDomainService, ExampleDomainService>();

unityContainer.RegisterType<IExampleWebService, ExampleWebService>();

ExampleWebService 类型及其构造函数如下所示：

[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class ExampleWebService
{
    public ExampleWebService(IExampleDomainService exampleDomainService)
    {
        this.exampleDomainService = exampleDomainService;
    }

// ...

和ExampleDomainService没有定义构造函数（当我为这种类型显式定义一个无参数构造函数时，问题是一样的）。

接下来，如 Unity.Wcf 的 documentation 中所述：

If you are hosting your WCF service within a Windows Service using a ServiceHost, replace the ServiceHost instance with the custom Unity.Wcf.UnityServiceHost. You will find that the UnityServiceHost takes in a Unity container as its first parameter but is otherwise identical to the default ServiceHost.

我执行以下操作：

 var host = new UnityServiceHost(unityContainer, typeof(ExampleWebService), baseAddress);

然而，这会抛出 System.InvalidOperationException 并显示以下消息：

The service type provided could not be loaded as a service because it does not have a default (parameter-less) constructor. To fix the problem, add a default constructor to the type, or pass an instance of the type to the host.

查看 UnityServiceHost implementation at GitHub 它将给定的 serviceType（在本例中为 typeof(ExampleWebService)）直接传递给 WCF 的本机 ServiceHost:

public sealed class UnityServiceHost : ServiceHost
{
    public UnityServiceHost(IUnityContainer container, Type serviceType, params Uri[] baseAddresses)
      : base(serviceType, baseAddresses)
             ^^^^^^^^^^^
             ???????????

这显然会崩溃，因为 ServiceHost 对 Unity 及其容器一无所知，并且在缺少无参数构造函数时无法应对。

Unity.Wcf 是否因 non-WAS/non-IIS 托管而完全崩溃，或者（我希望）我做的事情完全错误？

Answer 1

对不起，我不能告诉你为什么你有异常，但我希望能帮助你。

ServiceHost 不需要了解任何关于 Unity 的知识。 DI 通过实施 IInstanceProvider 并为每个注册服务行为

它对我有用，这是非常基本的应用程序哪个工作正常，也许你可以找到你的问题所在边

public class Program
{
    static void Main(string[] args)
    {
        var container = new UnityContainer();
        container.RegisterType<IDependency, Dependency>();
        container.RegisterType<IHelloWorldService, HelloWorldService>();
        Uri baseAddress = new Uri("http://localhost:8080/hello");
        using (ServiceHost host = new UnityServiceHost(container, typeof(HelloWorldService), baseAddress))
        {
            ServiceMetadataBehavior smb = new ServiceMetadataBehavior();
            smb.HttpGetEnabled = true;
            smb.MetadataExporter.PolicyVersion = PolicyVersion.Policy15;
            host.Description.Behaviors.Add(smb);

            host.Open();

            Console.WriteLine("The service is ready at {0}", baseAddress);
            Console.WriteLine("Press <Enter> to stop the service.");
            Console.ReadLine();

            host.Close();
        }
    }
}

[ServiceContract]
public interface IHelloWorldService
{
    [OperationContract]
    string SayHello(string name);
}

public interface IDependency
{

}

public class Dependency : IDependency { }

public class HelloWorldService : IHelloWorldService
{
    private readonly IDependency _dependency;

    public HelloWorldService(IDependency dependency)
    {
        _dependency = dependency;
    }

    public string SayHello(string name)
    {
        return string.Format("Hello, {0}", name);
    }
}

如果使用 InstanceContextMode.Single，WCF 不会调用 InstanceProvider。这就是 Unity.WCF 不能使用它的原因。详细答案可见here.

为什么来自 Unity.Wcf 的服务主机无法正确解析服务实例？

Why can't service host from Unity.Wcf resolve service's instance correctly?

c#

wcf

unity-container

.net-4.6