Using RhinoCommon to get the instance of another plugin

Replies to This Discussion

Permalink Reply by Jon Mirtschin on July 7, 2010 at 12:05pm

Hi Paul,

It depends exactly what you're doing. You can use reflection to link into another dotNet Plug-in (including loading it into the active process if it's not already). Of you can simply reference the associated dll into your project.

It sounds (not really a surprise) that you're doing something similar to the Geometry Gym plug-ins, in which the Grasshopper components are really just satellite collectors and receivers of data from the main Rhino plug-in. I don't think Rhinocommon is the link you are looking for to connect to other dll's of your own.

Hope you can make sense of it (or maybe others will explain better than me).

Cheers,

Jon

Permalink Reply by Paul N Jeffries on July 8, 2010 at 3:10am

Thanks Jon,

Yeah, reflection is how I did it in the old version, but I always considered that a bit of a hack and as I'm re-writing it to use RhinoCommon I was hoping to improve on it a bit. So I was hoping to be able to do something like:

linkObject = RhinoApp.GetPlugInObject("MyPluginName")

And then use linkObject to exchange data between grasshopper and my plugin. Only, linkObject always comes back Null. Obviously, I don't need RhinoCommon just to reference an assembly!

My real problem is that the RhinoCommon documentation just has "[Missing documentation for "M:Rhino.RhinoApp.GetPlugInObject(System.String)"]" where it should have actual documentation, so I'm not sure whether this is even supposed to work the way I want it to, whether it's not implemented yet or whether I'm just using it wrong.

Permalink Reply by Jon Mirtschin on July 8, 2010 at 3:41am

Hi Paul,

It's still very early in Rhinocommon, so it wouldn't be a surprise if it wasn't implemented yet.

It sounds like it could very well provide the handle to your plug-in and allow access to COM visible commands (this is only an assumption by me) for use in Python etc.

Guess we'll have to wait for a response from someone in the know at McNeel.

Permalink Reply by Steve Baer on July 8, 2010 at 10:19am

Hi guys,
Every function in RhinoCommon should be functional. In other words, there aren't any stubbed out functions with a "todo" comment in them.

I just updated the comments for Rhino.RhinoApp.GetPlugInObject on http://www.rhino3d.com/5/rhinocommon/ You may have to refresh your browser window to see the new contents. This does sound like the function you are looking for. This function loads your plug-in and calls the "GetPlugInObjectInterface" on your Rhino_DotNet plug-in class. The result of GetPlugInObjectInterface is then returned.

I just tested this with a Rhino_DotNet based plug-in and a python script. The Rhino_DotNet plug-in returns a class in GetPlugInObjectInterface that has a "Print" function. Then, in a python script, I wrote

import Rhino
pio = Rhino.RhinoApp.GetPlugInObject("SteveCS_Samples")
pio.Print()

You should also be able to directly access this class in your VB or C# code.

Permalink Reply by Paul N Jeffries on July 9, 2010 at 11:19am

Thanks Steve,

I've now looked into this a bit more and it does actually half-work. By setting a breakpoint in my plugin's GetPlugInObjectInterface() function I can see that it is in fact calling this function, which is returning my 'link' object.

However, for some reason that object never makes it to grasshopper. It's definitely returning an object from GetPlugInObjectInterface but in grasshopper it comes up as Nothing.

I tried just returning a string, and that did manage it. I think the problem is this: my 'link' object is my own custom object which is defined in a .dll which is referenced by both my plug-in and my grasshopper component. However when I use GetPlugInObject, this seems to be passing through something in RhinoCommon which is saying 'I don't know what the hell this is, get rid of it'. That's why this way doesn't work but doing something like (in the old SDK)

Dim SalPlugIn As MRhinoPlugIn = RhUtil.GetPlugInInstance(path)
Dim result As SAL_GrasshopperLink = SalPlugIn.GetPlugInObjectInterface(New System.Guid())

does, because it's accessing the plugin directly and both ends of the equation know what the object is.

So, what is the intended usage of the GetPlugInObject method, if you can't use your own objects? Have I totally misunderstood the intent? Will RhinoCommon include something which will let you access the plugin itself, so you can extract your PlugInObjectInterface yourself?

Permalink Reply by Steve Baer on July 9, 2010 at 1:02pm

There shouldn't be any difference. Are you running this in a debugger? If so, put a breakpoint on the line that calls Rhino.RhinoApp.GetPlugInObject. Does the debugger show that the return object is actually "Nothing"?

Permalink Reply by Paul N Jeffries on July 12, 2010 at 2:52am

Yup, that's what I did, so I'm pretty sure that's what is happening.

Don't worry about it too much for my sake, I've now figured out a sneaky way around it Though obviously if it is a bug it might be worth sorting out for the benefit of other people.

Permalink Reply by Steve Baer on July 12, 2010 at 10:43am

It would be nice to figure out what is going wrong since I don't want to make people rely on "sneaky workarounds". I would appreciate it if you could verify that you can
1. break on the line calling GetPlugInObject from your GH component
2. break in your plug-in function that returns an object
3. the return value from GetPlugInObject is Nothing (null)

Make sure that the line calling GetPlugInObject looks like

Dim obj As Object = Rhino.RhinoApp.GetPlugInObject("MyPlugIn")
If obj IsNot Nothing Then
Rhino.RhinoApp.WriteLine("I got something")
End If
Dim result As SAL_GrasshopperLink = obj

In other words, don't perform the cast on the same line that is calling GetPlugInObject. I want to make absolutely sure that the cast isn't the root of the problem.

Thanks.

Permalink Reply by Luis Fraguada on July 8, 2010 at 3:47am

If you have not done so already, submit this to the Rhino Plug-Ins Newsgroup. If it is not implemented, they can add it to the list.