Question

I have a winforms c# app that has an embedded webbrowser control inside it generated through VS.NET 2008. We sink events by inheriting our events class from HTMLDocumentEvents2.

 public class IEHTMLDocumentEvents : mshtml.HTMLDocumentEvents2
 {
     public bool onclick(mshtml.IHTMLEventObj pEvtObj)
     {
         // Clicking on an input (checkbox, radio, button, image)
         if (pEvtObj.srcElement.tagName == "INPUT")
         {
             // The following will result in a null pointer without VS.NET installed
             HTMLInputElementClass input = pEvtObj.srcElement as HTMLInputElementClass;
         }
     }
 }

The code above works fine when clicking on elements in the webbrowser control on our dev machines with VS.NET installed.
However it fails to cast the pEvtObj.srcElement when VS.NET is not installed. This immediately starts working when we install the most basic VS.NET with C# that you can.

To note: The rest of the c# app works fine, and you can browser the web through the control fine as well, just that the events like the above ‘onclick’ can’t be handled properly.

I thought it would be a DLL version loaded issue but doing a diff of the files loaded indicates only minor differences.

1c1
< Process: C# App without VS.NET installed
---
> Process: C# App with VS.NET 2008 installed
18d17
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\CustomMarshalers\e148983beeb0f30918b0564849a16456\CustomMarshalers.ni.dll CustomMarshalers.ni.dll Microsoft .NET Framework Custom Marshalers Microsoft Corporation 2.0.50727.3053
36d34
< C:\Documents and Settings\XpHome\Local Settings\History\History.IE5\index.dat index.dat   
37a36
> C:\Documents and Settings\XpHome\Local Settings\History\History.IE5\index.dat index.dat   
44,45c43,44
< C:\Program Files\<hidden>\<hidden>\Microsoft.mshtml.dll Microsoft.mshtml.dll     7.0.3300.1
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\Microsoft.VisualBas#\5b3d048d8c003d743ea5e72caf07773a\Microsoft.VisualBasic.ni.dll Microsoft.VisualBasic.ni.dll Visual Basic Runtime Library Microsoft Corporation 8.0.50727.3053
---
> C:\WINDOWS\assembly\GAC\Microsoft.mshtml\7.0.3300.0__b03f5f7f11d50a3a\Microsoft.mshtml.dll Microsoft.mshtml.dll     7.0.3300.1
> C:\WINDOWS\assembly\GAC_MSIL\Microsoft.VisualBasic\8.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualBasic.dll Microsoft.VisualBasic.dll Visual Basic Runtime Library Microsoft Corporation 8.0.50727.3053
50,52c49,51
< c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\mscorjit.dll mscorjit.dll Microsoft .NET Runtime Just-In-Time Compiler Microsoft Corporation 2.0.50727.3053
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\mscorlib\9adb89fa22fd5b4ce433b5aca7fb1b07\mscorlib.ni.dll mscorlib.ni.dll Microsoft Common Language Runtime Class Library Microsoft Corporation 2.0.50727.3053
< c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\mscorwks.dll mscorwks.dll Microsoft .NET Runtime Common Language Runtime - WorkStation Microsoft Corporation 2.0.50727.3053
---
> c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\mscorjit.dll mscorjit.dll Microsoft .NET Runtime Just-In-Time Compiler Microsoft Corporation 2.0.50727.3082
> C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\mscorlib\7124a40b9998f7b63c86bd1a2125ce26\mscorlib.ni.dll mscorlib.ni.dll Microsoft Common Language Runtime Class Library Microsoft Corporation 2.0.50727.3603
> c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\mscorwks.dll mscorwks.dll Microsoft .NET Runtime Common Language Runtime - WorkStation Microsoft Corporation 2.0.50727.3603
94,98c93,97
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Configuration\cb4cb21d14767292e079366a5d3d76cd\System.Configuration.ni.dll System.Configuration.ni.dll System.Configuration.dll Microsoft Corporation 2.0.50727.3053
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Drawing\6978f2e90f13bc720d57fa6895c911e2\System.Drawing.ni.dll System.Drawing.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System\aa7926460a336408c8041330ad90929d\System.ni.dll System.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Windows.Forms\9a254c455892c02355ab0ab0f0727c5b\System.Windows.Forms.ni.dll System.Windows.Forms.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
< C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Xml\36f3953f24d4f0b767bf172331ad6f3e\System.Xml.ni.dll System.Xml.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
---
> C:\WINDOWS\assembly\GAC_MSIL\System.Configuration\2.0.0.0__b03f5f7f11d50a3a\System.Configuration.dll System.Configuration.dll System.Configuration.dll Microsoft Corporation 2.0.50727.3053
> C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Drawing\abb2ac7e08bee026f857d8fa36f9fe6f\System.Drawing.ni.dll System.Drawing.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
> C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System\3de5bd01124463d7862bd173af90bc83\System.ni.dll System.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
> C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Windows.Forms\d2ea8d76f015817db1607075812b555f\System.Windows.Forms.ni.dll System.Windows.Forms.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3053
> C:\WINDOWS\assembly\NativeImages_v2.0.50727_32\System.Xml\5913d3f81e77194ec833991b1047a532\System.Xml.ni.dll System.Xml.ni.dll .NET Framework Microsoft Corporation 2.0.50727.3082

Answer 1

Ok, found the answer finally. It appears that even though it successfully loads the microsoft.mshtml.dll that we distribute with the app. The COM interfaces cannot be accessed unless you register it in the GAC on the client machine using regasm.exe.