Digital Dave

So for the past week or so, I’ve been really crunching down on two different plug-in architecture with C#: Reflection and System.AddIn.

Why?

Well, I want to create a much more robust 2D RPG editor than I’ve done in the past.  I want to give people the foundation to build off of while allowing me to learn how to make a dynamic tool that can continue to grow beyond what I do to it. And Jeff motivated me to do it.

I decided not to use Reflection because I really didn’t want to sit here and spend time creating all kinds of security links between my application and the plug-in.  While System.AddIn is incredibly tedious, I feel that it will be worth it in the long term.

So to get my hands dirty with the AddIn framework, I developed a plug-in based calculator prototype.

There are 3 different development pieces that construct the ‘pipeline’ between the application and the plug-in. The project structure is pretty strict. You can see that, here.

The Contract 

• Contract – Isolates the Plug-in for better sandboxing and robustness of the host application. Think of this as the formality that the HOST and the PLUG-IN must adhere to.

The Host:

• View – Defines how the HOST application sees the ADD-IN
• Adapter – Converts the CONTRACT to the HOST view
• Application – Your application

The Plug-In

• View – Defines the base class for the ADD-IN.  This is what you distribute to people, to build their plug-in from.
• Adapter – Converts the VIEW to the CONTRACT
• Implementation – Your plug-in

As far as plug-in development goes.  The only concern is with the AddIn view, which will be provided.  In it, we have our abstract class.

using System.AddIn.Pipeline;

namespace AddIn.View
{
[AddInBase]
public abstract class AddInView
{
public abstract int ComputeNums(int x, int y);
public abstract string GetSign();
}
}

Which can be used to actually define our method declarations.

using System.AddIn;
using AddIn.View;

namespace Addin.Addition
{
[AddIn("Addition Plug-In",
Version = "1.0",
Description = "Add 2 Numbers",
Publisher = "David McGraw")]
public class Addition : AddInView
{
public override int ComputeNums(int x, int y)
{
return (x + y);
}

public override string GetSign()
{
return “+”;
}
}
}

The application is build to search the plug-in directory for *.dll files, and will load them if they match the contract. As a plug-in developer, this is little of to no concern as long as you followed the view.

Play with the prototype here, if you want. I hold no promises that it won’t blow up your computer.  Feel free to implement divide, I provided the source for plug-in development.