GH_Structure of Object, VB, Visual Studio, GHA

Replies to This Discussion

Permalink Reply by Pirouz Nourian on October 16, 2013 at 9:00am

Hi, 

I found out that I need to get a Datatree(of Object) as a GH_Structure(of IGH_Goo), now my problem is how to convert data of type IGH_Goo to doubles, strings and colors!

Permalink Reply by David Rutten on October 16, 2013 at 9:30am

DataTree is only suppose to be used in VB/C#/Python script components. As you found out, when making a GHA project you need to get a GH_Structure(Of T).

GH_Structure(Of T) has a constraint on T which means it has to implement IGH_Goo. If your input is a Number Parameter then you can get a GH_Structure(Of GH_Number). If your input is a string parameter, then you can get a GH_Structure(Of GH_String).

GH_Number and GH_Integer and GH_Brep etc. all have a Value property that gives access to the value inside the goo class. You can also use the GH_Convert class to convert those grasshopper wrapper types into useful types.

--

David Rutten

david@mcneel.com

Seattle, WA

Permalink Reply by Pirouz Nourian on October 16, 2013 at 9:54am

Hi David, 

Thanks for replying from Seattle! The thing is, I have made a datatree of attributes, containing strings, doubles and colors, in order to make it easier for the user to provide them altogether. So I have defined it as a datatree(of object), so as to allow for containing different things. 

The following works in VS, but fails in GH when I drag in the built GHA.

Protected Overrides Sub SolveInstance(DA As IGH_DataAccess)
Dim Attributes As New GH_Structure(Of IGH_Goo)
Dim Tags As New List(Of String)
Dim Areas As New List(Of Double)
Dim Colors As New List(Of Color)
If DA.GetDataTree(Of IGH_Goo)(0, Attributes) Then
Tags = Attributes.Branch(0)
Areas = Attributes.Branch(1)
Colors = Attributes.Branch(2)
DA.SetDataList(0, Tags)
DA.SetDataList(1, Areas)
DA.SetDataList(2, Colors)
End If
End Sub

Do I need to iterate through every branch and convert them to strings, doubles and colors separately or there is a better way?

Thanks for your support,

Pirouz

Permalink Reply by David Rutten on October 16, 2013 at 2:15pm

That shouldn't work in Visual Studio. If it does, it means you're not working in Option Explicit mode in VB and you won't catch a lot of problems until you try and run your code.

Your GH_Structure(Of IGH_Goo) contains branches that are List(Of IGH_Goo). In order to get all this data into a List(Of String), you'll have to actually iterate over them*:

Dim areas As New List(Of String)

For Each gooArea As IGH_Goo in Attributes.Branch(1)

  If (gooArea Is Nothing) Then

    areas.Add(Double.NaN)

  Else

    Dim area As Double = Double.NaN

    GH_Convert.ToDouble(gooArea, area, GH_Conversion.Both)

    areas.Add(area)

  End If

Next

IGH_Goo can always be a null reference, so you have to check for that. Furthermore, data could be stored as GH_Integer or GH_String or something and only look like a double, so you're better off using GH_Convert.

If you're absolutely 100% certain that it can only ever be GH_Number, then you can write this:

...

Else

  areas.Add(DirectCast(gooTag, GH_Number).Value)

End If

--

David Rutten

david@mcneel.com

Seattle, WA

* There's probably ways using LINQ as well, but let's not go there today.

Permalink Reply by Pirouz Nourian on October 17, 2013 at 4:55am

Thank you very much for the explanation. However, I have 

Option Strict Off
Option Explicit On

on the top of everything and I don't get any errors in VS. Am I missing something else?

(BTW, I was trying to use a Linq method .cast (of ResultT) to do this but it didn't work either.) If it is just because of datatrees (GH_Structures), may be I should consider using a list(of list(of Object)) instead; is that a good idea (except for making it unreadable within GH)? I actually don't get the essence of the problem that for instance it is not possible to directly cast a GH_String to String or a GH_Number to Double? If I understood you correctly, I can convert their value properties but not themselves. Right? Could you please enlighten me a bit on the necessity of all such conversions?