C# About GH_ParamAccess type

Grasshopper Developer
1

I think GH_ParamAccess, besides Item, List and Tree, needs Onlyitem and Onlylist.

e.g. Wrap Input of List Item component should not be entered into a multiple item list. Of course, make menu items is a good solution, but it can’t be automated.
It need Onlyitem.

e.g. Path Input of Tree Branch component should not be entered into a multiple branch tree. and, make menu item doesn’t solve the problem.
It need Onlylist.

Of course, this essence is a compatibility issue, can also be solved with field.
I want Onlyitem to send a warning and just use the first item when the input data is a multiple items list. Onlylist is similar to this.

2

Sounds like you can perform those checks inside the component SolveInstance or BeforeSolveInstance methods just by looking at the input datatree.

private bool _validInputs;
protected override void BeforeSolveInstance()
{
  _validInputs = true;
  if (Params.Input[1].VolatileData.PathCount > 1)
  {
    AddRuntimeMessage(
      GH_RuntimeMessageLevel.Error, 
      "The second input may not contain more than a single list of items.");
    _validInputs = false;
  }
}

protected override void SolveInstance(IGH_DataAccess access)
{
  if (!_validInputs && access.Iteration > 0)
  {
    // Perhaps the Iteration check doesn't work for you, 
    // in which case the access.ParameterTargetIndex(int) or
    // access.ParameterTargetPath(int) may.
    access.DisableGapLogic();
    return;
  }
    ...
}
3

Thank you very much!