Best approach to extensibility on node types and context actions in Forms treeview

Question

I'm working on a Visual Studio Add-in for Visual Studio 2008 that display a treeview that provides a view on content in a server product. The server product contains different types of nodes, and each node has its own type of context menu (right click menu).

For new types of nodes and the actions connected to a node I currently just add code two my project. I would like to disconnect my node types and the actions available on a node in such a few that I can add nodes and entries to to context menu with a plugin model. MEF would probably be a good candidate. Does anyone have a good idea on how to implement this in a simple and straightforward way, so that especially the plugin developer does not have to do a lot of plumbing?

Answer 1

I would provide a common library that both your code and the plugin libraries all link to (call this the Contract dependency). In there, define an interface for a node type, like INodeType. Also, consider implementing an AbstractNodeType in there that implements INodeType and provides some helpful properties that the plugin author can set in their constructor.

One of the properties of INodeType is a ContextMenu property that returns a windows forms context menu.

In your code make a property:

[Import("NodeTypes", typeof(INodeType))]
public IEnumerable<INodeType> extensionNodeTypes { get; set; }

You can just enumerate through that after you've composed.

In the plugin code, they would declare new node types something like this (may not compile):

[Export("NodeTypes", typeof(INodeType))]
public class SomeNodeType : AbstractNodeType
{
    public SomeNodeType()
    {
        this.ContextMenu = base.BuildContextMenu(/* ... */);
        /* etc. */
    }
    /* ... other custom logic ... */
}

I hope I didn't mess up the syntax, but that's the general idea.