Custom Component Reading a List

Replies to This Discussion

Permalink Reply by David Rutten on July 22, 2010 at 1:56am

You need to supply an existing (but empty) list of data if you want to use GetDataList

Dim SeedCurve As New List(Of Curve)
If (Not DA.GetDataList(0, SeedCurve)) Then Return


The error message actually is pretty accurate...

"Target List is a null reference. GH_IndexList.GetDataList() can only be called with a constructed List."


--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by kermin chok on July 22, 2010 at 8:45am

David,
Thanks for the info. So now the plot thickens. What if the user may provide a list of curves or a single curve? How might we set up code so we don't throw an error when we are reading a data item but a list is coming in and vice versa?

Do I have to do anything special at the

pManager.Register_CurveParam("xxxx")

declaration for passing in a list or a single item?

Furthermore, I'm still getting this error when trying to pass in the list of curves.

Thanks again.

kermin

Permalink Reply by David Rutten on July 22, 2010 at 12:19pm

Kermin,

you can't. If the input is a list parameter you must always accept the whole list. When someone supplies only a single item, you may decide to switch to a different branch of logic of course, but you must use GetDataList().

I cannot read the text in the image. When you upload images there's an option to link to the unscaled original. Please check it.

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by kermin chok on July 22, 2010 at 12:49pm

Permalink Reply by David Rutten on July 23, 2010 at 12:20am

Hi Kermin,

it seems you are still calling GetDataList() on a parameter that has been set to item access. When you construct the parameter in RegisterInputParams, you have to pick Item (default), List or Tree. From this point onwards you should only use GetData(), GetDataList() or GetDataTree() respectively.

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by kermin chok on July 23, 2010 at 8:57am

Thanks. That worked. I guess it would help if I scrolled through the rest of the options for declaring input parameters.

Anything I should know about outputing items, list or trees? Or is the output parameter more flexible in that it adapts to whatever it is set to.

Thanks again.

Kermin

Permalink Reply by David Rutten on July 23, 2010 at 9:33am

The output is more flexible, though you should probably stick to the same SetDataXXXX() method inside your SolveInstance function.

I haven't tested how it behaves when you call SetData on some iterations and SetDataList on others.

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by kermin chok on July 28, 2010 at 4:33pm

David,

Do you have an example for reading in a datatree? I'm trying this so far and it's not the correct syntax.

Do I have to declare an empty tree or something like that?


pManager.Register_PointParam("Pts", "Pts", "Reaction Points", GH_ParamAccess.tree)
End Sub

Dim ReactionPts As New DataTree(Of Point)
If Not (DA.GetDataTree(0, ReactionPts)) Then Return


Thanks.

kermin