Plug In Design for .NET App

Question

I’m looking at rewriting a portion of our application in C# (currently legacy VB6 code). The module I am starting with is responsible for importing data from a variety of systems into our database. About 5-6 times a year, a new client asks us to write a new import for the system that they use. Presently, this requires us to release a new version of our software for each new import option we add to the application.

One of the goals of the rewrite is to make the application support plug-ins. Every new import can become a separate assembly which the host application will recognize and allow the end user to interact with. This will hopefully simplify life to some degree as we can simply drop a new assembly into the directory and have it be recognized and used by the main (host) application.

One of the items I am struggling with relates to the differences between the import options we currently support. In some cases we actually let the user point to a directory and read all of the files within the directory into our system. In other cases we allow them to point to a single file and import its contents. Additionally, some imports have a date range restriction that the user applies while others do not.

My question is, how can I design the application in a manner that allows for some flexibility among the imports we build and support while at the same time implementing a common interface that will allow the host application to easily recognize the plug-ins and the options that each one exposes to the user?

Answer 1

I would recommend you take a look at the Managed Add-In Framework that shipped with .NET 3.5. The Add-In team has posted some samples and tools at CodePlex site as well..

Answer 2

.Net 3.5 has the system.Addin namespace.

This thread also has some good information for older versions of the framework:
http://forums.devshed.com/net-development-87/system-plugin-532149.html

Answer 3

for the theory take a look at the plugin pattern in martin fowlers Patterns of Enterprise Application Architecture

for an interesting example take a look at this tutorial: Plugin Architecture using C#