Question

我试图去DI一个继承EventArgs的类。当我将这个类改为我所拥有的一个单独的类时，我不断收到错误，说它“没有隐式引用转换。”

以下是VerificationStatusEventArgs类的声明。

namespace Jimbob.CsvImporter.DataVerification
{
    public interface IVerificationStatusEventArgs
    {
        string SummaryMessage { get; set; }

        bool CarriedOutToCompletion { get; set; }

        List<String> ErrorLog { get; set; }
    }

    public class VerificationStatusEventArgs:EventArgs, IVerificationStatusEventArgs
    {
        public string SummaryMessage { get; set; }

        public bool CarriedOutToCompletion { get; set; }

        public List<String> ErrorLog { get; set; }
    }
}

我试图将此注入到下面的类中，但是不能使用接口声明事件。

public interface ICsvFileVerification
{
//Error here (1)
    event EventHandler<IVerificationStatusEventArgs> VerificationCompleted;

    event EventHandler UpdateProgressBar;

    //..
}

public class CsvFileVerification : ICsvFileVerification
{
    IUserInputEntity _entity;
    IEntityVerification _entityVerification;
    IVerificationStatusEventArgs _dataVerificationStatus;


    public CsvFileVerification(IEntityVerification entityVerification, IVerificationStatusEventArgs dataVerificationStatus)
    {
        _entityVerification = entityVerification;
        _dataVerificationStatus = dataVerificationStatus;
    }
//Error here (2)
    public event EventHandler<IVerificationStatusEventArgs> VerificationCompleted;
    public event EventHandler UpdateProgressBar;

    public void VerifyDataManagerAsync()
    {
        _dataVerificationStatus.CarriedOutToCompletion = true;
        _dataVerificationStatus.ErrorLog = new List<string>();

        if (!_cancelToken.IsCancellationRequested)
        {
            try
            {
                _entityVerification.VerifyUserInputManager(_entity, _dataVerificationStatus.ErrorLog);
                if (_dataVerificationStatus.ErrorLog.Count > 0)
                {
                    _dataVerificationStatus.CarriedOutToCompletion = false;
                    _dataVerificationStatus.SummaryMessage = "Verification of user inputs failed.";
                    return;
                }

                VerifyDataTypes();
            }

            catch (Exception Ex)
            {
                //...
            }

            finally
            {
                //Call method to raise event.
                OnVerificationStatusEventArgs(this, _dataVerificationStatus);
            }
        }
        else
        {
            _dataVerificationStatus.SummaryMessage = "Operation was canceled before the task could be started." + Environment.NewLine;
            _dataVerificationStatus.CarriedOutToCompletion = false;
            OnVerificationStatusEventArgs(this, _dataVerificationStatus);
        }
    }


    /// <summary>
    /// Raises an event on the GUI thread which should be used to notify the user that the task is
    /// completed and, if relevant, the exception message that was thrown.
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected virtual void OnVerificationStatusEventArgs(object sender, IVerificationStatusEventArgs e)
    {
//Error here (3)
        EventHandler<IVerificationStatusEventArgs> TempHandler = VerificationCompleted;

        //Avoid possible race condition.
        if (TempHandler != null)
        {
            TempHandler(this, e);
        }
    }

错误：（1），（2）＆amp; （3）：

The type 'Jimbob.CsvImporter.DataVerification.IVerificationStatusEventArgs' cannot be used as type parameter 'TEventArgs' in the generic type or method 'System.EventHandler<TEventArgs>'. 

There is no implicit reference conversion from 'Jimbob.CsvImporter.DataVerification.IVerificationStatusEventArgs' to 'System.EventArgs'.

主要目的是为了测试VerifyDataManagerAsync（）。我想这实际上只能用VerificationStatusEventArgs类的一个实例来完成。

c＃chat中有人建议在.net 4.0中这不可行吗？是这种情况还是有解决方法？

感谢。

Answer 1

定义：

delegate System.EventArgs<TEventArgs> where TEventArgs : EventArgs

表示括号内的任何内容都必须从EventArgs继承。 IVerificationStatusEventArgs不会继承EventArgs。您可以通过创建继承自EventArgs的抽象类来继承您的继承链。然后继承它。

public abstract class VerificationStatusEventArgsBase : EventArgs
{
    //some abstract methods here
}

public class VerificationStatusEventArgs : VerificationStatusEventArgsBase 
{
    //implement your abstract methods
}

然后它应该工作。

P.S。您可以阅读有关泛型here的约束。

DI一个继承自EventArgs的类？

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