VB.NET 2005 Daily Lesson [6.27.07] - Recursive TreeNode Creation

ccoonen · #1 (**permalink**) 06-27-2007, 07:48 AM

If you are ever working with a TreeView control, which is what Windows Explorer uses to explore Files and Folders, then you will realize that recursion is the only way to go. The TreeView control uses a TreeNode as a datasource and is n-level with infinite parent, children, nodes, leaves etc... Here is a function that will build your TreeNode recursively by taking a ParentNode as a treenode, adds a node, finds all children, adds all children, and repeat.

This is built off a Strongly Typed Dataset with an ID field that link to it's parent in the same field. For example, Fishing would have ID 5 and a ParentID of 0... Fishing would be a Root Item, but Fly Fishing would have a ParentID of 5 so it is a child of Fishing.

Code:

 Private Shared Function GetAllTreeNodes(ByRef CategoryItem As Category, ByRef ParentNode As TreeNode) As TreeNode
  Dim NewParentNode As New TreeNode
  If ParentNode.Text = "" Then
    NewParentNode = ParentNode.Nodes.Add("ROOT_LEVEL_NODE", " Categories")
    NewParentNode.Tag = -1
  Else
    NewParentNode = ParentNode.Nodes.Add(CategoryItem.CategoryID, CategoryItem.Name)
    NewParentNode.Tag = CategoryItem.CategoryID
  End If

  Using CategoryAdapter As New DAL.TableAdapters.CategoryTableAdapter()
    Using CategoryTable As DAL.CategoryDataTable = CategoryAdapter.GetByParentCategoryID(CategoryItem.CategoryID)
      For Each CategoryRow As DAL.CategoryRow In CategoryTable
        GetAllTreeNodes(ConstructObjFromDataRow(CategoryRow), NewParentNode)
      Next
    End Using
  End Using
  Return NewParentNode
End Function

HelloWorld · #2 (**permalink**) 06-27-2007, 04:50 PM

Thanx for the nice tutorial, even I won't actually try it until I'm done with C#.NET

ccoonen · #3 (**permalink**) 06-27-2007, 07:35 PM

No problem, hope it helps some people out... it can be used with anything to create a recursive structure

HelloWorld · #4 (**permalink**) 06-27-2007, 08:20 PM

Quote:

Originally Posted by ccoonen

No problem, hope it helps some people out... it can be used with anything to create a recursive structure

Why do you think that Recursion is the only way to go? Can't we go with the Iterative way? Since, it's just basically the same thing.. however, I'm pretty sure that Iterative way is going to be much more complicated...?

ccoonen · #5 (**permalink**) 06-27-2007, 08:46 PM

well... you can iterate to how ever many levels you program it for you know?

Code:

 If you say:
for x = 0 to ubound(datasource)
  for y = 0 to ubound(datasource(x))
    for z = 0 to ubound(datasource(x)(y))
    ......
    next
  next
next

That's 3 levels deep. With recursion it can go Unlimited levels deep. You can have parent, child, child, child, child, child, child, etc... iinfinite levels (n-level). This is why recursion is the only way because their is not telling how "deep" the levels go