Question

I am trying to come up with a Menu and Context menu architecture similar to what Visual Studio 2010 offers so that I could extend my current Menu with additional subitems provided by extensions. I am using MEF (Managed Extensibility Framework).
As an example, the Resharper extension adds menu items and context menu items in any possible position (top, middle or bottom of the context menu or a menu item)
How could one go to provide such a functionality? Do I have to index every single menu item of the shell and have the extension refer to the index to position its on subitems?
I hope that my question is clear enough. If not I would be more than happy to add some clarification.

Answer 1

I’m not sure there’s a single best way to do this. But here are some ideas to consider:

A fairly simple solution is to use a single contract (ie IMenuIten) and use metadata to control what menu the command appears in and in what position. One way to do this is to have an “index”, although it should probably be a double and used to sort the items in a menu so each item doesn’t need to know its absolute position in the menu. Another way is to have metadata on the menu items that gives a list of other items that should be before and after the current item. Then you can do a topological sort on the menu items to get an order to display them in.

Depending on how complex/dynamic your menu behavior needs to be, you may find that you can’t express it well using export metadata. In this case you might move the functionality to the contract itself- ie adding properties or methods on your IMenuItem contract. That way you can run code to calculate the values you need.

Another solution is not to export menu items directly at all. Instead, you can have a menu service that is imported by a component. The service would have a Register method which would add a menu item to a menu. In my opinion this makes adding menu items quite a bit more cumbersome so I wouldn’t recommend it unless there’s a reason you need it. It might be appropriate if the available menu items should change based on the current context of the application. Note that if you do go this way, just having a class that imports the menu service won’t cause the class to be created and composed. The class needs to export something that is imported somewhere else in the system.