This thread is for discussions of Writing Plugin-Based Applications.

Hi.

I've been trying to find the way of doing an application with pluggable components over vb6, but have not found any help. I read the subject of this article and was very excited but when I realized it was about .net I got frustrated. Could you please explain me how it is possible to make a plugin-based app in vb6.
Thanx

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malloc

I can't get AvailablePlugin to work. VB.NET reports that
"Type 'AvailablePlugin' is not defined." Has anyone else had this problem?

I noticed that when I used [Assembly].LoadFrom(), it kept on loading the first plugin that was initially loaded,
to fix this; use [Assembly].LoadFile() insted.

DotNet Framework 1.1, Visual Studio 2003, Visual Basic.NET.

The complete code is available in the source code, however I'll post it for you anyway.

Code:

   Public Structure AvailablePlugin
       Public AssemblyPath As String
       Public ClassName As String
   End Structure

Enjoy!

Hi Tim,

I think your article is great, i'm looking for it for months, and finally...

I just have a question:

If I want that a plugin add a button ont the host form, is it possible? can you help me please?

thanks in advance,
Ivan

Great article!

This will come in very handy with an application I have in mind .

Just a note about using this in VB2005 (I'm using Express edition right now, hopefully I'll upgrade):

The CreateInstance method of the PluginServices works fine, and does return an instance of the class that can be used but only when put into an Object type.

You don't have the full list of functions and subroutines available to you using the object.

When using the DirectCast, to cast the instance to an variable declared as the Interface - it doesn't like that cast and throws an exception.

To fix this do what Prozac mentiond - change the references of [Assembly].LoadFrom() to [Assembly].LoadFile() and it works fine.

Thanks for the great article!

This artice was just what I was looking for - however it turned out to lead me to the conclusion that the feature I wanted wasn't achievable by .Net - at least not without some dirty coding... You code describes plugging in, but not plugging out. To my shock I realized that .Net doesn't allow unloading of assemblies!

I needed the plug in functionality to swap and update plug-ins on a regular basis, for an ASP.Net application. However, it seems I must shut down the site completely to replace an existing plug-in with a new version...

I rewrote your application in C# and everthing works except one thing.

After loading  assembly and creating plugin instance I am casting plugin instance to plugin interface and I get excepion "Specified cast is not valid"

I have no idea what is wrong.

I liked this article, all seven times that I read it. But I felt that it lacked a bit of security. I came across this article on msdn. It shows quite nicely how to wrap untrusted code in a sort of security blanket.

Hi There,

I found a very easy way to add controls to the host.

The interface should have this:    
Now you are able to add an control to the host like this:
Me.ToolStripContainer1.TopToolStripPanel.Controls.Add(objPlugin.InitializeMenu)

The only thing i did not figure out yet is how to handle when you click on the control.

Just add event handlers to the menu items before returning from InitializeMenu, e.g.

menu1.Click += new EventHandler (nameOfCallbackFunction);