Creating a component from Visual Studio: input parameters

Replies to This Discussion

Permalink Reply by David Rutten on June 26, 2012 at 3:35pm

There is no Polyline type in Grasshopper. You'll have to either use the Curve parameter, or create your own type and parameter.

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Miguel Vidal on June 27, 2012 at 3:39am

Ok, David. I was using the Curve parameter (pManager.Register_CurveParam) but, when I feed the input with of the component with a polyline, I get the error: "Invalid cast Curve >> Polyline".

Shouldn´t  the component be casting the Polyline as a Curve?

Anyway, could you explain how could I create my own parameter? Is it on the GH SDK help file?

Thank you! :)

Permalink Reply by David Rutten on June 27, 2012 at 3:55am

Polylines can always be cast to curves, but not all curves can be cast to polylines. Is the casting error from within the SolveInstance() method or from elsewhere?

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Miguel Vidal on June 27, 2012 at 4:23am

It must be from the SolveInstance() I suppose because both the input and output params are set as CurveParam.

Permalink Reply by David Rutten on June 27, 2012 at 5:17am

You should get a Rhino.Geometry.Curve if the parameter is of type curve. Then convert the curve to a polyline if possible, if not, post a runtime message informing the user that only polylines are accepted.

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Miguel Vidal on June 27, 2012 at 11:40am

Right.

But, in the case of using curves and then converting them to polylines, how could I declare at the beginning a placeholder variable and initialize a curve, as this class is protected?

Rhino.Geometry.Curve crv = new Rhino.Geometry.Curve(); is not valid

Permalink Reply by David Rutten on June 27, 2012 at 12:45pm

You don't have to initialize it, the DA.GetData will do that for you:

Curve curve = null;

if (!DA.GetData(0, ref curve)) { return; }

Polyline polyline;
if (!crv.TryGetPolyline(out polyline))
{
  AddRuntimeMessage(GH_RuntimeMessageLevel.Error,

                                 "Only polylines are accepted");
  return;
}

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Miguel Vidal on June 28, 2012 at 10:59am

Thanks, David.

Now that works just fine but I have trouble outputting DataTrees with DA.SetData.

The Grasshopper component returns items and lists but the outputs that should be returning DataTrees have nothing.

How could I fix that?

 Thank you!

Permalink Reply by Miguel Vidal on June 28, 2012 at 11:23am

Sorry David, the problem is within SolveInstance(). It´s not about DataTrees.

Permalink Reply by David Rutten on June 28, 2012 at 11:38am

You cannot use DataTrees, they are just for scripters. You'll need to construct a GH_Structure<IGH_Goo T>, then assign it using DA.SetDataTree().

Creating structures is quite tricky though, are you absolutely sure you have to do it this way?

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Miguel Vidal on June 28, 2012 at 1:13pm

So, in order to output a collection of objects, I have to use lists, right?

Actually, I was making a component out of a script I made and I was using DataTrees in this one.

It would be intersting to know how to use them but I would use lists if it´s very tricky though.

Permalink Reply by David Rutten on June 28, 2012 at 1:40pm

The problem with outputting trees is that you have to make sure they have the correct paths. If the SolveInstance() method is called more than once in a solution you have to make sure your trees are merged in an odd way.

But let's start another thread for this as this one has reached its response limit.

If you want to use DA.SetDataList, then you need to supply an IEnumerable instance. A list will do. So will an array, or any other class that implements IEnumerable.

--

David Rutten

david@mcneel.com

Poprad, Slovakia