error:object reference not set to an instance of an object

private void RunScript(DataTree<Polyline> c, DataTree<int> storey, DataTree<Point3d> vpt, int high, ref object A)
{
DataTree<Polyline> temp = new DataTree<Polyline>();
GH_Path pth = new GH_Path(0, 0);
temp.Branch(pth)[0] = c.Branch(0)[0];
A = temp;
}

why the output is:error:object reference not set to an instance of an object(of the red line)?

Thank you very much!!!

Replies to This Discussion

Permalink Reply by David Rutten on December 5, 2011 at 3:06pm

"Object reference not set to an instance of an object" is the most common exception in .NET as far as I know. It means you're trying to call a method on a class which doesn't exist. Or rather, a class which hasn't been instantiated.

In this case your temp DataTree has been constructed but it is empty. I.e. it has no paths and no branches. So when you ask for the branch at pth, you'll get a null reference in return. Then you try and call [0] on that null reference, which is what throws the exception.

I cannot tell you how to fix it until you tell me what it is you're trying to do.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Andrea Lu on December 5, 2011 at 3:19pm

Thank you David for reply,I have understood your explaination.

than,later i try this,and works:

private void RunScript(DataTree<Polyline> c, DataTree<int> storey, DataTree<Point3d> vpt, int high, ref object A)
{
DataTree<Polyline> temp = new DataTree<Polyline>(c);
GH_Path pth = new GH_Path(0, 0);
temp.Add(c.Branch(0)[0], pth);
A = temp;
}

Permalink Reply by aleksmkd on February 12, 2014 at 6:21pm