So earlier today I saw the needs for a dll plugin system and coded one. There is a API.dll and a Default.dll along with my Program.exe

Plugins/Default.dll

API.dll

Program.exe

My question is whats the best way to go about this ? I want Program.exe to have the same types in API.dll but if I put those types in Program.exe and reference it from API.dll I would be able to explicity add the classes from 'Default.dll' via Assembly into Program.exe via static calls. But then I would need to re-define the type in API.dll which wouldnt be to hard as I can just reference the ones already in Program.exe

So whats your thoughts and opinions on this one ?

Use Unity ? http://msdn.microsoft.com/en-us/library/dd203101.aspx

Thanks for the reply "PhillipHamlyn" but I can already load the classes and such within the plugins into my program so there is no need for external libraries, I simply want some input regarding how I should have the structure.

Example:

API.dll references Program.exe

Default.dll references API.dll

Program.exe loads all 'Plugins/*.dll' and pulls the classes from the plugins storing there types.

Program.exe then when in need of using the plugin types does "IMyPluginBaseType TheCreatedClass = (IMyPluginBaseType) Assembly.CreateInstance( Type.FullName );"

I store the data as such, Dictionary<String,Type>; The string being a unique id generated when the type is parsed from the dll.

Currently I have Program.exe and Default.dll referencing API.dll as it's the easier meens of doing things.

Oh, I see.

If its a true plugin, the Program should not know about the Types inside the plugin - it should only share a set of Types (probably only Interfaces) made available for the plugin to consume, so for each plugin, as you say, there is only one Type you care about (which is the name of the Type implementing the Plugin interface). I'd probably parse the plugin assembly using reflection and pick up the class implementing the plugin Interface and instantiate it using CreateInstance as you suggest. Where is the need for Program to store the Types in the plugin ? I think I'm missing something ?

Philip

Well thats actually how I am doing things, as for the types that get loaded into the program they get parsed by a static class in my Main file. It grabs all the types from the plugins that implement classes or interfaces within API.dll So the types that implement ANY class in API.dll get added to a list for usage later in my program.

My main reason for posting this thread was to get input on how I should go about this and it would seem given your response that the way I've been planing to do it would indeed by recommended by you.

Sounds a lot like a thread I wrote ages ago? Would you be looking for this:

http://nccastaff.bournemouth.ac.uk/jmacey/RobTheBloke/www/CSPluginExample2.zip

I actually ported that to the latest .NET framework the other day. The code more or less still works (although I had to create new project files because for some unknown reason I couldn't get the project files to upgrade successfully - and couldn't be bothered to find out why). If you want to avoid the compiler warnings, modify the code like so:

[source]

I already have what I was looking for... But anyway that is very intresting code non the less, though I don't currently have use for it.

For everyone interested, here is the article (from GameDev) that taught me how to build plugin systems over 10 years ago:

http://www.gamedev.net/page/resources/_/technical/multiplayer-and-network-programming/why-pluggable-factories-rock-my-multiplayer-world-r841

it is a very helpful article and I have used its core ideas a dozen times since (the implementation details vary by language - but the core concept of derived types "registering" themselves is the key).