Adding child node to treeview

Question

ProjectNumbers = DatabaseHandler.Instance.QuerySingleColumn(SelectProjectNumberQuery, "ProjectNumber");
      foreach (string ProjectNumber in ProjectNumbers)
      {
             ProjectTree.Nodes.Add(ProjectNumber);
             ProjectTree.EndUpdate();
             SelectWorkOrderNumberQuery = "SELECT DISTINCT WorkOrderNumber FROM dbo.SUBPRODUCTS WHERE ProjectNumber =" + Int32.Parse(ProjectNumber) + ";";
             WorkOrderNumbers = DatabaseHandler.Instance.QuerySingleColumn(SelectWorkOrderNumberQuery, "WorkOrderNumber");
                  foreach(string WorkOrderNumber in WorkOrderNumbers)
                  {                 
                      ProjectTree.Nodes[ProjectNumber].Nodes.Add(WorkOrderNumber); 
                  }
      }

I'm trying to fill my ProjectTree with ProjectNumbers and WorkOrderNumbers from an SQL database. The ProjectTree.Nodes.Add(ProjectNumber) is working fine within the first foreach loop.

When adding my WorkOrderNumber as a child (second foreach loop), I'm getting the object with no reference error, cant quite figure out why. Found some related topics where they use the SelectedNode() function, but that doesn't work for me.

Possible duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — yaakov, May 02 '16 at 07:47

score 0 · Accepted Answer · answered May 02 '16 at 08:03

Lets try this :

 ProjectNumbers = DatabaseHandler.Instance.QuerySingleColumn(SelectProjectNumberQuery, "ProjectNumber");
          foreach (string ProjectNumber in ProjectNumbers)
          {
                                 var node = new TreeNode(ProjectNumber);

                 SelectWorkOrderNumberQuery = "SELECT DISTINCT WorkOrderNumber FROM dbo.SUBPRODUCTS WHERE ProjectNumber =" + Int32.Parse(ProjectNumber) + ";";
                 WorkOrderNumbers = DatabaseHandler.Instance.QuerySingleColumn(SelectWorkOrderNumberQuery, "WorkOrderNumber");
                      foreach(string WorkOrderNumber in WorkOrderNumbers)
                      {                 
                            var workNode = new TreeNode(WorkOrderNumber);
                    node.Nodes.Add(workNode);
                      }
 ProjectTree.Nodes.Add(node);
          }

Do you know *why* retaining a reference to the node works, but looking it up again fails? — yaakov, May 02 '16 at 08:17
because ProjectTree.Nodes[ProjectNumber] looking for a key, but when you add a node you just set a title for it — Mahdi Farhani, May 02 '16 at 08:23

Adding child node to treeview

1 Answers1