GetDataTree with costum generic data types

Grasshopper Developer
,
1

Dear forum,
I am writing a GH plug-in where I’ve created a class called Plank. Into the current component,which I am writing, a tree of Planks are feed. I’ve written a code that compiles, but when I try the component out, I get the following error message:

  1. Solution exception:Unable to cast object of type ‘Grasshopper.Kernel.Types.GH_ObjectWrapper’ to type ‘geoPlankNetworks.DataTypes.Plank’.

And this is my code

protected override void RegisterInputParams(GH_Component.GH_InputParamManager pManager)
    {
        pManager.AddGenericParameter("Plank", "p", "p", GH_ParamAccess.tree);
    }

protected override void RegisterOutputParams(GH_Component.GH_OutputParamManager pManager)
    {
        pManager.AddBrepParameter("Mid surface", "mS", "mS", GH_ParamAccess.tree);
        pManager.AddBrepParameter("Top surface", "tS", "tS", GH_ParamAccess.tree);
        pManager.AddBrepParameter("Bottom surface", "bS", "bS", GH_ParamAccess.tree);
        pManager.AddBrepParameter("Plank solid","pS","pS",GH_ParamAccess.tree);
    }

protected override void SolveInstance(IGH_DataAccess DA)
    {
        GH_Structure<IGH_Goo> iPlankTree;

        if (!DA.GetDataTree(0, out iPlankTree)) return;

        DataTree<Brep> midSurfaces = new DataTree<Brep>();
        DataTree<Brep> topSurfaces = new DataTree<Brep>();
        DataTree<Brep> bottomSurfaces = new DataTree<Brep>();
        DataTree<Brep> plankSolids = new DataTree<Brep>();

        foreach(GH_Path path in iPlankTree.Paths)
        {
            foreach(Plank plank in iPlankTree.get_Branch(path)) 
            {                    
                midSurfaces.Add(plank.MidSurface, path);
                topSurfaces.Add(plank.TopSurface, path);
                bottomSurfaces.Add(plank.BottomSurface, path);
                plankSolids.Add(plank.PlankSolid, path);
            }
        }

        DA.SetDataTree(0,midSurfaces);
        DA.SetDataTree(1,topSurfaces);   
        DA.SetDataTree(2,bottomSurfaces);
        DA.SetDataTree(3,plankSolids);
    }

It would be great if someone could help me out here.
Thanks,
David

2

Hi,

It’s hard to say without the complete class but a few ideas :

  • foreach(Plank plank in iPlankTree.get_Branch(path))

Maybe you can’t iterate through a branch with a custom type
You may want to try something like this :

foreach(IGH_Goo ighgoo in iPlankTree.get_Branch(path))
{
if(ighgoo.Value is Plank p)
{
...
}
}

  • Define the input parameter of the component as a Plank, not a Data, following this guide. Rhino - Simple Parameters

  • Do you really need this component as tree ? It is best to have the input structures as simple as possible. You could have this as item and let Grasshopper handle the trees for you.

3

What do you mean with this? I set the input to “item” but I feed a tree anyways?

4

Yes, the vast majority of components in GH work like that.
You’ll have to change your access type to GH_ParamAccess.item and the input and output methods DA.GetData(0, ref blablabla) and DA.SetData(0, blablabla).

5

But how do I then access the branches and paths?

6

You can’t, but it doesn’t seem you need to with your current code.

7

yes I do. I want to keep the tree structure created earlier in the GH definition.

8

Yes, but the component will do that for you. I mean, you don’t need to access the tree structure inside the component, since all you are doing is converting each element of the tree independently.

9

yes, you are right! wow, this is so much easier. Thanks a lot!