C# WCF Singleton服务错误：无法将提供的服务类型作为服务加载，因为它没有默认构造函数

我对WCF有以下奇怪的问题，我无法找出原因：

我正在与WCF合作，以确定是否将其用于需要为类似打印机的设备实现的远程控制API。该设备由运行.Net中实现的控制器软件的Windows PC控制。我需要为这个软件实现API

该服务是控制器软件内部的自托管服务，我目前正在研究如何创建WCF服务的单例实例，以便使用控制器软件创建具有相应对象/类的实例。我已经使用简化版本实现了这一点，但奇怪的是，如果服务不包含默认（无参数）构造函数，我会得到这个警告。更奇怪的是，我正在做的正是第二句中例外告诉我的（或者至少我喜欢认为我是）。此异常在标题为“WCF服务主机”的单独窗口中引发，程序随后继续正常执行：

System.InvalidOperationException:无法将提供的服务类型作为服务加载，因为它没有默认（无参数）构造函数。要解决此问题，请向该类型添加默认构造函数，或将该类型的实例传递给主机

位于System.ServiceModel.Description.ServiceDescription.CreateImplementation（类型serviceType）

位于System.ServiceModel.Description.ServiceDescription.SetupSingleton（ServiceDescription ServiceDescription，对象实现，布尔值是众所周知的）

位于System.ServiceModel.Description.ServiceDescription.GetService（类型serviceType）

位于System.ServiceModel.ServiceHost.CreateDescription（IDictionary`2&implementedContracts）

位于System.ServiceModel.ServiceHostBase.InitializeDescription（UrischemeKeydCollection基地址）

位于System.ServiceModel.ServiceHost..ctor（类型serviceType，Uri[]baseAddresses）

在Microsoft.Tools.SvcHost.ServiceHostHelper.CreateServiceHost（类型，ServiceKind）

位于Microsoft.Tools.SvcHost.ServiceHostHelper.OpenService（ServiceInfo信息）

下面是我用来创建服务的代码。我在

Service.cs

中注释了包含默认构造函数的注释行。有趣的是，当我包含默认构造函数（因此永远不会抛出错误）时，它永远不会被调用（我通过设置断点确认了这一点）。如果您取消了注释，则不会引发异常

Server.cs

：

public class Server
{
    private ServiceHost svh;
    private Service service;

    public Server()
    {
        service = new Service("A fixed ctor test value that the service should return.");
        svh = new ServiceHost(service);
    }

    public void Open(string ipAdress, string port)
    {
        svh.AddServiceEndpoint(
        typeof(IService),
        new NetTcpBinding(),
        "net.tcp://"+ ipAdress + ":" + port);
        svh.Open();
    }

    public void Close()
    {
        svh.Close();
    }
}

    [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant,
                 InstanceContextMode = InstanceContextMode.Single)]
public class Service : IService
{
    private string defaultString;

    public Service(string ctorTestValue)
    {
        this.defaultString = ctorTestValue;
    }

    
    //// when this constructor is uncommented, I do not get the error
    //public Service()
    //{
    //    defaultString = "Default value from the ctor without argument.";
    //}

    public string GetDefaultString()
    {
        return defaultString;
    }

    public string GetData(int value)
    {
        return string.Format("You entered: {0}", value);
    }

    public CompositeType GetDataUsingDataContract(CompositeType composite)
    {
        if (composite == null)
        {
            throw new ArgumentNullException("composite");
        }
        if (composite.BoolValue)
        {
            composite.StringValue += "Suffix";
        }
        return composite;
    }

    public string Ping(string name)
    {
        Console.WriteLine("SERVER - Processing Ping('{0}')", name);
        return "Hello, " + name;
    }

    static Action m_Event1 = delegate { };

    static Action m_Event2 = delegate { };

    public void SubscribeEvent1()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event1 += subscriber.Event1;
    }

    public void UnsubscribeEvent1()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event1 -= subscriber.Event1;
    }

    public void SubscribeEvent2()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event2 += subscriber.Event2;
    }

    public void UnsubscribeEvent2()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event2 -= subscriber.Event2;
    }

    public static void FireEvent1()
    {
        m_Event1();
    }

    public static void FireEvent2()
    {
        m_Event2();
    }

    public static Timer Timer1;
    public static Timer Timer2;

    public void OpenSession()
    {
        Timer1 = new Timer(1000);
        Timer1.AutoReset = true;
        Timer1.Enabled = true;
        Timer1.Elapsed += OnTimer1Elapsed;

        Timer2 = new Timer(500);
        Timer2.AutoReset = true;
        Timer2.Enabled = true;
        Timer2.Elapsed += OnTimer2Elapsed;
    }

    void OnTimer1Elapsed(object sender, ElapsedEventArgs e)
    {
        FireEvent1();
    }

    void OnTimer2Elapsed(object sender, ElapsedEventArgs e)
    {
        FireEvent2();
    }

}

    public interface IMyEvents
{
    [OperationContract(IsOneWay = true)]
    void Event1();

    [OperationContract(IsOneWay = true)]
    void Event2();
}

// NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IService1" in both code and config file together.
[ServiceContract(CallbackContract = typeof(IMyEvents))]
public interface IService
{
    [OperationContract]
    string GetData(int value);

    [OperationContract]
    string GetDefaultString();

    [OperationContract]
    CompositeType GetDataUsingDataContract(CompositeType composite);

    // TODO: Add your service operations here
    [OperationContract]
    string Ping(string name);

    [OperationContract]
    void SubscribeEvent1();

    [OperationContract]
    void UnsubscribeEvent1();

    [OperationContract]
    void SubscribeEvent2();

    [OperationContract]
    void UnsubscribeEvent2();

    [OperationContract]
    void OpenSession();
}

// Use a data contract as illustrated in the sample below to add composite types to service operations.
// You can add XSD files into the project. After building the project, you can directly use the data types defined there, with the namespace "WcfService.ContractType".
[DataContract]
public class CompositeType
{
    bool boolValue = true;
    string stringValue = "Hello ";

    [DataMember]
    public bool BoolValue
    {
        get { return boolValue; }
        set { boolValue = value; }
    }

    [DataMember]
    public string StringValue
    {
        get { return stringValue; }
        set { stringValue = value; }
    }
}

Service.cs

：

public class Server
{
    private ServiceHost svh;
    private Service service;

    public Server()
    {
        service = new Service("A fixed ctor test value that the service should return.");
        svh = new ServiceHost(service);
    }

    public void Open(string ipAdress, string port)
    {
        svh.AddServiceEndpoint(
        typeof(IService),
        new NetTcpBinding(),
        "net.tcp://"+ ipAdress + ":" + port);
        svh.Open();
    }

    public void Close()
    {
        svh.Close();
    }
}

    [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant,
                 InstanceContextMode = InstanceContextMode.Single)]
public class Service : IService
{
    private string defaultString;

    public Service(string ctorTestValue)
    {
        this.defaultString = ctorTestValue;
    }

    
    //// when this constructor is uncommented, I do not get the error
    //public Service()
    //{
    //    defaultString = "Default value from the ctor without argument.";
    //}

    public string GetDefaultString()
    {
        return defaultString;
    }

    public string GetData(int value)
    {
        return string.Format("You entered: {0}", value);
    }

    public CompositeType GetDataUsingDataContract(CompositeType composite)
    {
        if (composite == null)
        {
            throw new ArgumentNullException("composite");
        }
        if (composite.BoolValue)
        {
            composite.StringValue += "Suffix";
        }
        return composite;
    }

    public string Ping(string name)
    {
        Console.WriteLine("SERVER - Processing Ping('{0}')", name);
        return "Hello, " + name;
    }

    static Action m_Event1 = delegate { };

    static Action m_Event2 = delegate { };

    public void SubscribeEvent1()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event1 += subscriber.Event1;
    }

    public void UnsubscribeEvent1()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event1 -= subscriber.Event1;
    }

    public void SubscribeEvent2()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event2 += subscriber.Event2;
    }

    public void UnsubscribeEvent2()
    {
        IMyEvents subscriber = OperationContext.Current.GetCallbackChannel<IMyEvents>();
        m_Event2 -= subscriber.Event2;
    }

    public static void FireEvent1()
    {
        m_Event1();
    }

    public static void FireEvent2()
    {
        m_Event2();
    }

    public static Timer Timer1;
    public static Timer Timer2;

    public void OpenSession()
    {
        Timer1 = new Timer(1000);
        Timer1.AutoReset = true;
        Timer1.Enabled = true;
        Timer1.Elapsed += OnTimer1Elapsed;

        Timer2 = new Timer(500);
        Timer2.AutoReset = true;
        Timer2.Enabled = true;
        Timer2.Elapsed += OnTimer2Elapsed;
    }

    void OnTimer1Elapsed(object sender, ElapsedEventArgs e)
    {
        FireEvent1();
    }

    void OnTimer2Elapsed(object sender, ElapsedEventArgs e)
    {
        FireEvent2();
    }

}

    public interface IMyEvents
{
    [OperationContract(IsOneWay = true)]
    void Event1();

    [OperationContract(IsOneWay = true)]
    void Event2();
}

// NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IService1" in both code and config file together.
[ServiceContract(CallbackContract = typeof(IMyEvents))]
public interface IService
{
    [OperationContract]
    string GetData(int value);

    [OperationContract]
    string GetDefaultString();

    [OperationContract]
    CompositeType GetDataUsingDataContract(CompositeType composite);

    // TODO: Add your service operations here
    [OperationContract]
    string Ping(string name);

    [OperationContract]
    void SubscribeEvent1();

    [OperationContract]
    void UnsubscribeEvent1();

    [OperationContract]
    void SubscribeEvent2();

    [OperationContract]
    void UnsubscribeEvent2();

    [OperationContract]
    void OpenSession();
}

// Use a data contract as illustrated in the sample below to add composite types to service operations.
// You can add XSD files into the project. After building the project, you can directly use the data types defined there, with the namespace "WcfService.ContractType".
[DataContract]
public class CompositeType
{
    bool boolValue = true;
    string stringValue = "Hello ";

    [DataMember]
    public bool BoolValue
    {
        get { return boolValue; }
        set { boolValue = value; }
    }

    [DataMember]
    public string StringValue
    {
        get { return stringValue; }
        set { stringValue = value; }
    }
}

Main

用于启动服务器：

static void Main(string[] args)
{
    // start server
    var server = new Server();
    server.Open("localhost", "6700");
    Console.WriteLine("Server started.");

    Console.ReadLine();
    server.Close();
}

---

该问题是由在Visual Studio中调试时运行的WcfSvcHost引起的。根据“WCF服务主机枚举WCF服务项目中的服务，加载项目的配置，并为找到的每个服务实例化一个主机。该工具通过WCF服务模板集成到Visual Studio中，并在您开始调试项目时调用。”

---

您不需要使用WCF服务主机，因为您是自托管的，所以您可以通过包含该服务的项目的“项目属性”页面禁用它。您应该在属性页上看到“WCF选项”选项卡。在此情况下，请关闭“调试时启动WCF服务主机…”选项。

我复制了您的代码并从我的环境中运行了它，但问题没有出现。WcfSvcHost在VS中调试时是否正在运行？请参阅。@KimJohnson在您的建议之后，我尝试从VS外部启动我的小测试程序（没有默认的无参数构造函数），但我没有得到上面描述的错误。所以我猜这可能与你的建议有关。然而，在阅读了你提供的链接后，我仍然不明白到底是什么问题。还有什么建议吗？顺便说一句：我忘了在我的问题中提到：通过设置断点，我确认，默认的ctor（当存在时）永远不会被调用。谢谢并致以最诚挚的问候。看起来它正在尝试承载您的代码的早期版本。清理您的环境，删除bin和obj文件夹。@CodeCaster感谢您的建议。我尝试删除bin和obj文件夹，并执行解决方案->清理->重建。删除bin文件夹时，我发现Windows告诉我无法删除它，因为它正在使用中。关闭VS后，我可以删除它。不幸的是，错误依然存在。还有其他建议吗？可能是因为某种原因，它启动了两个服务或其他什么？奇怪的是……这就成功了，当程序启动时，工具栏上的“恼人的”WcfHostService弹出窗口就消失了。非常感谢！