将 .NET 事件公开给 COM？

我一直在尝试向 VBA 客户端公开并触发事件。到目前为止，在 VBA 客户端，事件已公开，并且我看到方法事件处理方法已添加到我的模块类中，但是 VBA 事件处理方法不会触发。由于某种原因，调试时事件为空。同步修改我的代码也没有帮助。

作为记录，我检查了其他问题，但没有帮助。

任何好的答案将不胜感激。

[ComVisible(true)]
[Guid("56C41646-10CB-4188-979D-23F70E0FFDF5")]
[ClassInterface(ClassInterfaceType.None)]
[ComSourceInterfaces(typeof(IWebEvents))]
[ProgId("MyAssembly.MyClass")]
public class MyClass : ServicedComponent, IMyClass
{
    public string _address { get; private set; }
    public string _filename { get; private set; }

    [DispId(4)]
    public void DownloadFileAsync(string address, string filename)
    {
        _address = address;
        _filename = filename;
        System.Net.WebClient wc = new System.Net.WebClient();
        Task.Factory.StartNew(() => wc.DownloadFile(_address, _filename))
            .ContinueWith((t) =>
        {
            if (null != this.OnDownloadCompleted)
                OnDownloadCompleted();
        });
    }
    public event OnDownloadCompletedEventHandler OnDownloadCompleted;
}

[ComVisible(false)]
public delegate void OnDownloadCompletedEventHandler();

[ComVisible(true)]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface IWebEvents
{
    [DispId(1)]
    void OnDownloadCompleted();
}

.NET 代码中的关键概念是将事件定义为单独接口上的方法，并通过以下方式将其连接到类[ComSourceInterfacesAttribute]。在示例中，这是使用此代码完成的[ComSourceInterfaces(typeof(IEvents))] where IEvents接口定义应在 COM 客户端上处理的事件。

事件命名注意事项：
C#类中定义的事件名称和接口上定义的接口方法名称必须相同。在这个例子中IEvents::OnDownloadCompleted对应于DemoEvents::OnDownloadCompleted.

然后定义了第二个接口，它代表类本身的公共API，这里称为IDemoEvents。在此接口上定义了在 COM 客户端上调用的方法。

C# 代码（构建为 COMVisibleEvents.dll）

using System;
using System.Diagnostics;
using System.EnterpriseServices;
using System.IO;
using System.Net;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace COMVisibleEvents
{
    [ComVisible(true)]
    [Guid("8403C952-E751-4DE1-BD91-F35DEE19206E")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface IEvents
    {
        [DispId(1)]
        void OnDownloadCompleted();

        [DispId(2)]
        void OnDownloadFailed(string message);
    }

    [ComVisible(true)]
    [Guid("2BF7DA6B-DDB3-42A5-BD65-92EE93ABB473")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface IDemoEvents
    {
        [DispId(1)]
        Task DownloadFileAsync(string address, string filename);
    }

    [ComVisible(true)]
    [Guid("56C41646-10CB-4188-979D-23F70E0FFDF5")]
    [ClassInterface(ClassInterfaceType.None)]
    [ComSourceInterfaces(typeof(IEvents))]
    [ProgId("COMVisibleEvents.DemoEvents")]
    public class DemoEvents : ServicedComponent, IDemoEvents
    {
        public delegate void OnDownloadCompletedDelegate();
        public delegate void OnDownloadFailedDelegate(string message);

        public event OnDownloadCompletedDelegate OnDownloadCompleted;
        public event OnDownloadFailedDelegate OnDownloadFailed;

        private string FileNamePath(string filename) 
            => Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), filename);

        public async Task DownloadFileAsync(string address, string filename)
        {
            try
            {
                using (var webClient = new WebClient())
                {
                    await webClient
                        .DownloadFileTaskAsync(new Uri(address), FileNamePath(filename))
                        .ContinueWith(t =>
                        {
                            if (t.Status == TaskStatus.Faulted)
                            {
                                var failed = OnDownloadFailed;
                                failed?.Invoke(GetExceptions(t));
                            }
                            else
                            {
                                var completed = OnDownloadCompleted;
                                completed?.Invoke();
                            }
                        }, TaskScheduler.FromCurrentSynchronizationContext());
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.ToString());
            }

            #region Local

            string GetExceptions(Task task)
            {
                var innerExceptions = task.Exception?.Flatten().InnerExceptions;
                if (innerExceptions == null)
                    return string.Empty;
                var builder = new StringBuilder();
                foreach (var e in innerExceptions)
                    builder.AppendLine(e.Message);
                return builder.ToString();
            }

            #endregion Local
        }
    }
}

regasm

C:\Windows\Microsoft.NET\Framework\v4.0.30319>regasm C:\Temp\COMVisibleEvents\bin\Debug\COMVisibleEvents.dll /tlb: C:\Temp\COMVisibleEvents\bin\Debug\COMVisibleEvents.tlb

注册 COM 互操作

在本地计算机上的开发过程中使用此设置。https://stackoverflow.com/a/3700057/863240 https://stackoverflow.com/a/3700057/863240

VBA 客户端参考*.tlb file

添加参考*tlb这是由生成的regasm。这里是这个的名字tlb文件是COMVisibleEvents.

这里使用 Excel 用户表单作为 VBA 客户端。单击按钮后，该方法DownloadFileAsync被执行，当该方法完成时，事件被处理程序捕获m_eventSource_OnDownloadCompleted。在此示例中，您可以从 datahub.io 下载机场代码。

VBA 客户端代码 (MS Excel 2016)

Option Explicit

Private WithEvents m_eventSource As DemoEvents

Private Sub DownloadFileAsyncButton_Click()
    m_eventSource.DownloadFileAsync "https://datahub.io/core/airport-codes/r/airport-codes.json", "airport-codes.json"
End Sub

Private Sub m_eventSource_OnDownloadCompleted()
    MsgBox "Download completed..."
End Sub

Private Sub m_eventSource_OnDownloadFailed(ByVal message As String)
    MsgBox "Download failed. " & message, vbCritical, "Error"
End Sub

Private Sub UserForm_Initialize()
    Set m_eventSource = New COMVisibleEvents.DemoEvents
End Sub

Result

源代码也在 GitHub 上：

https://github.com/ddmail/COMVisibleEvents.git https://github.com/ddmail/COMVisibleEvents.git