GetData() can only be called on a parameter with access set to GH_ParamAccess.item

Replies to This Discussion

Permalink Reply by Andrew Heumann on October 6, 2012 at 12:21pm

"The fact that the Param Access is set to list in this case means that the Solve instance is running once for every item in the list (of strings) but this should not influence the GetData() method which runs once every time." - this is wrong, as David says in the section you quoted, for list access solve instance runs once for each list, not for each item in the list. 

When you get your data as a list, you have to use DA.GetDataList, and operate on the List object.

Permalink Reply by Arthur Mamou-Mani on October 6, 2012 at 12:32pm

Thanks Andrew!

I have added DA.GetDataList:

protected override void RegisterInputParams(GH_Component.GH_InputParamManager pManager)
{
pManager.AddTextParameter("SomeString", "SS", "Send Some String Somwhere", GH_ParamAccess.list); //0
}
protected override void SolveInstance(IGH_DataAccess DA)
{

string SomeString = default(string);
DA.GetDataList(0, ref SomeString);

if (!DA.GetDataList(0, ref SomeString)) return;

}

 

I get the following error on the DA.GetDataList line though:

`The type arguments for method 'Grasshopper.Kernel.IGH_DataAccess.GetDataList<T>(int, System.Collections.Generic.List<T>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.`

Permalink Reply by Arthur Mamou-Mani on October 6, 2012 at 12:57pm

Sorry, I guess I need to specify a list of string and not a string:

List<string> someStrings = new List<string>();
if(! DA.GetDataList(0, someStrings)) return;

 

Permalink Reply by John Harding on March 25, 2013 at 4:33pm

Sorry, bit late on this one but the problem is not the datatype being a string, but that you were using the 'ref' keyword. 

For example, the following works fine:

pm.Register_IntegerParam("Some numbers", "I", "Some numeric stuff", GH_ParamAccess.list);

....

List<int> myStuff = new List<int>();
if (!DA.GetDataList<int>(0, myStuff)) { return; }

Probably too late, but might help others.

Permalink Reply by Godjenka on May 5, 2016 at 3:59pm

Hey I tried this with a Data Tree and it doesnt work. I know this post is 3 years old but I am still hoping you could answer. Thank you

Permalink Reply by Mateusz Zwierzycki on May 5, 2016 at 4:43pm

When outside of scripting components, you should use GH_Structure instead of DataTrees. As far as I remember, you can set tree for the output parameter, but you have to use GH_Structure with the inputs.

Permalink Reply by Godjenka on May 18, 2016 at 9:34am

Hey, 

I was wondering if you had an example of a GH_Path for GH_structure in visual studio to access items in a tree with Get_DataItem? In the SDK, it is just written that it should be a series of integers but they didn't specify the exact form?

Thank you

Permalink Reply by Natalie Chelliah on October 10, 2012 at 5:31am

Hi,

I am getting this error message and I am not sure what do to - reading thius doesnt make much sense to me so if somebody could explain in simpler terms?

Thanks

Natalie

Permalink Reply by Andrew Heumann on October 10, 2012 at 11:45am

Are you getting it on a component that you yourself are writing? or is it showing up as an error in an existing grasshopper component (or one from an add-in)?

Permalink Reply by Murtaza Mohammadi on March 21, 2018 at 5:40pm

Hi, Thanks for your suggestion guys. Worked well for me