Creating add-ons for WPF applications

Question

I have a simple database application where an user can add or delete persons. Moreover, the application has a button "Add new button to application". This application is built using Prism framework. There are two modules:

• RibbonControlModule (contains three buttons - Add Person, Delete Person, Add new button to application)

• PersonModule (contains logic of adding and deleting persons)

My requirement is to add new buttons at runtime.

Let's imagine a situation. I live in Washington and I am happy with these two buttons(Add Person and Delete Person). But my friend, Bob, who lives in New Jersey would like to add new button Edit Button without recompilation the whole application. That is, Bob writes dll where he can edit person and then clicks Add new button to application in RibbonControlModule. After that, EditPerson button is appeared in RibbonControl and, for example, in ContextMenu. Maybe EditPerson dll would be another Prism module, I do not know.

That is, my requirements are:

• pluggable controls
• is it possible to plug control without recompliation? (like add-ons or extensions(Classic Notes for Opera) in Browsers(no need to restart a browser to use add-ons))
• other programmers can develop their add-ons without using my source code
• after once an user plugged a control, then this new control should be always plugged in the application.

Is it possible using WPF, MVVM and Prism? I really like Prism and do not want to deny Prism, but if "the end justifies the means", I would like to use other technologies.

If it is possible, then how can I do it?

Answer 1

This is what the MEF plugin architecture was designed for.

In short, you create an SDK containing an interface for your plugins and provide that to your clients as a standalone library. Your client's plugins then implement this interface and export them with the MEF Export attribute, which your main application then imports.

Where it gets a little tricky is with data templating, which is often a key component of MVVM. To cut a long story short your plugins need to put their data templates in a resource dictionary, give that dictionary it's own partial class file and export it with MEF's [Export] attribute. Your main app then needs to import these and add them to the global ResourceDictionary's 'MergedDictionaries' array. This is generally done separate to all your view model classes which are imported in a separate pass. The net effect is that your plugins can provides both views and view models at runtime, plus the data templates that bind the two together, and it will all work as though they'd been statically compiled into your original application. It also means you can create a plugin API for your customers without exposing the internals of your main application.

This is a very involved topic, and given how general this question is I'll be surprised if this question isn't flagged. If you'd like more details then let me know and we can move it to a discussion page.