blocks|key|112630|text|.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[ComSourceInterfacesAttribute]将其连接到类。在该示例中，这是使用以下代码接口完成的，其中IEvents接口定义了应该在COM客户端上处理的事件。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|112631|事件命名注意事项：|112632|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。在本例中，IEvents::OnDownloadCompleted对应于DemoEvents::OnDownloadCompleted。|112633|然后定义第二个接口，它表示类本身的公共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。|112634|112635|+C#代码(构建到COMVisibleEvents.dll)|blockquote|112636|112637|112638|using+System;
using+System.EnterpriseServices;
using+System.IO;
using+System.Net;
using+System.Runtime.InteropServices;
using+System.Threading.Tasks;

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

++++[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();
++++++++private+event+OnDownloadCompletedDelegate+OnDownloadCompleted;
++++++++public+string+_address+{+get;+private+set;+}
++++++++public+string+_filename+{+get;+private+set;+}
++++++++private+readonly+string+_downloadToDirectory+=+
++++++++++++Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

++++++++public+async+Task+DownloadFileAsync(string+address,+string+filename)
++++++++{
++++++++++++try
++++++++++++{
++++++++++++++++using+(WebClient+webClient+=+new+WebClient())
++++++++++++++++{
++++++++++++++++++++webClient.Credentials+=+new+NetworkCredential(
++++++++++++++++++++++++"user",+"psw",+"domain");
++++++++++++++++++++string+file+=+Path.Combine(_downloadToDirectory,+filename);
++++++++++++++++++++await+webClient.DownloadFileTaskAsync(new+Uri(address),+file)
++++++++++++++++++++++++.ContinueWith(t+=>
++++++++++++++++++++++++{
++++++++++++++++++++++++++++//+https://stackoverflow.com/q/872323/
++++++++++++++++++++++++++++var+ev+=+OnDownloadCompleted;
++++++++++++++++++++++++++++if+(ev+!=+null)
++++++++++++++++++++++++++++{
++++++++++++++++++++++++++++++++ev();
++++++++++++++++++++++++++++}
++++++++++++++++++++++++},+TaskScheduler.FromCurrentSynchronizationContext());
++++++++++++++++}
++++++++++++}
++++++++++++catch+(Exception+ex)
++++++++++++{
++++++++++++++++//+Log+exception+here+...
++++++++++++}
++++++++}
++++}
}|code-block|syntax|javascript|112639|112640|正则表达式|112641|112642|112643|C:\Windows\Microsoft.NET\Framework\v4.0.30319>regasm+C:\Temp\COMVisibleEvents\bin\Debug\COMVisibleEvents.dll+/tlb:+C:\Temp\COMVisibleEvents\bin\Debug\COMVisibleEvents.tlb|112644|对*.tlb文件的|112645|+VBA客户端引用|112646|112647|112648|添加对regasm生成的*tlb的引用。这里，此tlb文件的名称为COMVisibleEvents。|112649|​|112650|📷|atomic|112651|112652|这里使用Excel用户表单作为VBA客户端。单击按钮后，将执行方法DownloadFileAsync，当此方法完成时，将在处理程序m_eventSource_OnDownloadCompleted中捕获事件。在本例中，您可以从my+dropbox下载C#项目COMVisibleEvents.dll的源代码。|112653|112654|+VBA客户端代码(MS+Excel2007)|112655|112656|112657|Option+Explicit

Private+WithEvents+m_eventSource+As+DemoEvents

Private+Sub+DownloadFileAsyncButton_Click()
++++m_eventSource.DownloadFileAsync+"https://www.dropbox.com/s/0q3dskxopelymac/COMVisibleEvents.zip?dl=0",+"COMVisibleEvents.zip"
End+Sub

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

Private+Sub+UserForm_Initialize()
++++Set+m_eventSource+=+New+COMVisibleEvents.DemoEvents
End+Sub|112658|112659|结果|112660|112661|112662|112663|112664|112665|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/4f6f90ab85253f038c07b27314e59c7b.jpeg|imageAlt|1|https://ask.qcloudimg.com/http-save/yehe-900000/f0fe858d0e58cef15d927e7934bdac28.jpeg^0|V|U|2I|7|0|0|Y|S|1T|V|0|R|B|0|0|0|0|0|0|0|0|0|0|0|1|5|0|0|0|0|3|6|C|4|O|3|X|G|0|0|0|1|0|0|0|X|H|1T|X|0|0|0|0|0|0|0|0|0|0|0|0|1|1|0|0^^$0|@$1|2|3|4|5|6|7|29|8|@$9|2A|A|2B|B|C]|$9|2C|A|2D|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|2E|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|2F|8|@$9|2G|A|2H|B|C]|$9|2I|A|2J|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|2K|8|@$9|2L|A|2M|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|2N|8|@]|D|@]|E|$]]|$1|M|3|N|5|O|7|2O|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|2P|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|2Q|8|@]|D|@]|E|$]]|$1|R|3|S|5|T|7|2R|8|@]|D|@]|E|$U|V]]|$1|W|3|-4|5|6|7|2S|8|@]|D|@]|E|$]]|$1|X|3|Y|5|O|7|2T|8|@]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|2U|8|@]|D|@]|E|$]]|$1|10|3|-4|5|6|7|2V|8|@]|D|@]|E|$]]|$1|11|3|12|5|T|7|2W|8|@]|D|@]|E|$U|V]]|$1|13|3|14|5|6|7|2X|8|@$9|2Y|A|2Z|B|C]]|D|@]|E|$]]|$1|15|3|16|5|O|7|30|8|@]|D|@]|E|$]]|$1|17|3|-4|5|6|7|31|8|@]|D|@]|E|$]]|$1|18|3|-4|5|6|7|32|8|@]|D|@]|E|$]]|$1|19|3|1A|5|6|7|33|8|@$9|34|A|35|B|C]|$9|36|A|37|B|C]|$9|38|A|39|B|C]|$9|3A|A|3B|B|C]]|D|@]|E|$]]|$1|1B|3|1C|5|6|7|3C|8|@]|D|@]|E|$]]|$1|1D|3|1E|5|1F|7|3D|8|@]|D|@$9|3E|A|3F|1|3G]]|E|$]]|$1|1G|3|1C|5|6|7|3H|8|@]|D|@]|E|$]]|$1|1H|3|1I|5|6|7|3I|8|@$9|3J|A|3K|B|C]|$9|3L|A|3M|B|C]]|D|@]|E|$]]|$1|1J|3|-4|5|6|7|3N|8|@]|D|@]|E|$]]|$1|1K|3|1L|5|O|7|3O|8|@]|D|@]|E|$]]|$1|1M|3|-4|5|6|7|3P|8|@]|D|@]|E|$]]|$1|1N|3|-4|5|6|7|3Q|8|@]|D|@]|E|$]]|$1|1O|3|1P|5|T|7|3R|8|@]|D|@]|E|$U|V]]|$1|1Q|3|-4|5|6|7|3S|8|@]|D|@]|E|$]]|$1|1R|3|1S|5|O|7|3T|8|@]|D|@]|E|$]]|$1|1T|3|-4|5|6|7|3U|8|@]|D|@]|E|$]]|$1|1U|3|-4|5|6|7|3V|8|@]|D|@]|E|$]]|$1|1V|3|1C|5|6|7|3W|8|@]|D|@]|E|$]]|$1|1W|3|1E|5|1F|7|3X|8|@]|D|@$9|3Y|A|3Z|1|40]]|E|$]]|$1|1X|3|1C|5|6|7|41|8|@]|D|@]|E|$]]|$1|1Y|3|-4|5|6|7|42|8|@]|D|@]|E|$]]]|1Z|$20|$5|21|22|23|E|$24|25|26|-4]]|27|$5|21|22|23|E|$24|28|26|-4]]]]

The key concept in .NET code is to define event(s) as method(s) on a separate interface and connect it to the class via <code>[ComSourceInterfacesAttribute]</code>. In the example this is done with this code <code>[ComSourceInterfaces(typeof(IEvents))]</code> where <code>IEvents</code> interface defines the event(s) which should be handled on COM client.
Note to event naming: 
Event names defined in c# class and interface method names defined on interface must be the same. In this example <code>IEvents::OnDownloadCompleted</code> corresponds with <code>DemoEvents::OnDownloadCompleted</code>.
Then a second interface is defined which represents the public API of the class itself, here it is called <code>IDemoEvents</code>. On this interface methods are defined which are called on COM client.
<blockquote>
C# code (builds to COMVisibleEvents.dll)
</blockquote>
<pre class="lang-cs prettyprint-override"><code>using System;
using System.EnterpriseServices;
using System.IO;
using System.Net;
using System.Runtime.InteropServices;
using System.Threading.Tasks;

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

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

 [ComVisible(true)]
 [Guid(&quot;56C41646-10CB-4188-979D-23F70E0FFDF5&quot;)]
 [ClassInterface(ClassInterfaceType.None)]
 [ComSourceInterfaces(typeof(IEvents))]
 [ProgId(&quot;COMVisibleEvents.DemoEvents&quot;)]
 public class DemoEvents
 : ServicedComponent, IDemoEvents
 {
 public delegate void OnDownloadCompletedDelegate();
 private event OnDownloadCompletedDelegate OnDownloadCompleted;
 public string _address { get; private set; }
 public string _filename { get; private set; }
 private readonly string _downloadToDirectory = 
 Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

 public async Task DownloadFileAsync(string address, string filename)
 {
 try
 {
 using (WebClient webClient = new WebClient())
 {
 webClient.Credentials = new NetworkCredential(
 &quot;user&quot;, &quot;psw&quot;, &quot;domain&quot;);
 string file = Path.Combine(_downloadToDirectory, filename);
 await webClient.DownloadFileTaskAsync(new Uri(address), file)
 .ContinueWith(t =&gt;
 {
 // https://stackoverflow.com/q/872323/
 var ev = OnDownloadCompleted;
 if (ev != null)
 {
 ev();
 }
 }, TaskScheduler.FromCurrentSynchronizationContext());
 }
 }
 catch (Exception ex)
 {
 // Log exception here ...
 }
 }
 }
}
</code></pre>
<blockquote>
regasm
</blockquote>
<pre class="lang-none prettyprint-override"><code>C:\Windows\Microsoft.NET\Framework\v4.0.30319&gt;regasm C:\Temp\COMVisibleEvents\bin\Debug\COMVisibleEvents.dll /tlb: C:\Temp\COMVisibleEvents\bin\Debug\COMVisibleEvents.tlb
</code></pre>
<blockquote>
VBA client reference to <code>*.tlb</code> file
</blockquote>
Add reference to <code>*tlb</code> which was generated by <code>regasm</code>. Here the name of this <code>tlb</code> file is <code>COMVisibleEvents</code>.
<a href="https://i.stack.imgur.com/yIQ5k.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yIQ5k.jpg" alt="enter image description here" /></a>
Here Excel User Form was used as VBA client. After the button was clicked, the method <code>DownloadFileAsync</code> was executed and when this method completes the event was caught in handler <code>m_eventSource_OnDownloadCompleted</code>. In this example you can download the source codes of the C# project COMVisibleEvents.dll from my dropbox.
<blockquote>
VBA client code (MS Excel 2007)
</blockquote>
<pre class="lang-vb prettyprint-override"><code>Option Explicit

Private WithEvents m_eventSource As DemoEvents

Private Sub DownloadFileAsyncButton_Click()
 m_eventSource.DownloadFileAsync &quot;https://www.dropbox.com/s/0q3dskxopelymac/COMVisibleEvents.zip?dl=0&quot;, &quot;COMVisibleEvents.zip&quot;
End Sub

Private Sub m_eventSource_OnDownloadCompleted()
 MsgBox &quot;Download completed...&quot;
End Sub

Private Sub UserForm_Initialize()
 Set m_eventSource = New COMVisibleEvents.DemoEvents
End Sub
</code></pre>
<blockquote>
Result
</blockquote>
<a href="https://i.stack.imgur.com/NUtJ0.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NUtJ0.jpg" alt="enter image description here" /></a>

I've been trying to expose and fire an event to a VBA client. So far on the VBA client side, the event is exposed and I see the method event handling method added to my module class however the VBA event handling method does not fire. For some reason, when debugging the event is null. Modifying my code with synchronously did not help either. 

For the record, I've checked other SO questions but they didn't help.

Any good answers will be appreciated.

<pre><code>[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(() =&gt; wc.DownloadFile(_address, _filename))
 .ContinueWith((t) =&gt;
 {
 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();
}
</code></pre>

This is a good gig for you all bounty hunters, 200 rep points

Exposing .NET events to COM?

Windows

我一直在尝试向VBA客户端公开和触发事件。到目前为止，在VBA客户端，事件是公开的，我看到方法事件处理方法被添加到我的模块类中，但是VBA事件处理方法没有触发。由于某些原因，在调试时事件为null。使用synchronously修改我的代码也没有任何帮助。根据记录，我已经检查了其他SO问题，但它们都没有帮助。任何好的答...

问将.NET事件暴露给COM？
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