Save and load the contents of a TreeView to and from a file

How do you save and load the contents of a TreeView to and from a file? I've been asked this question several times and I've also seen it pop up a few times on the VB-World Q and A forums so I thought it would be useful here in the tips library.

This code makes use of the Contents property of a PropertyBag object. This property was introduced in VB6 so VB5 users can't use these routines I'm afraid.

What it does

The code consists of two public Sub routines called SaveTree and LoadTree. The SaveTree procedure takes 3 arguments:

1. The file name (including the path) to where you want the file to be saved. The TreeView control of which contents you want to save.
2. The root node: The node you want the save to begin with. You can pass any valid node and the procedure will save the contents from that node and below.
3. The SaveTree procedure calls a private Sub called FillPropBag which is doing the actual job of filling the PropertyBag that is saved. It does this in a recursive manner.

The LoadTree procedure takes two arguments: the file name you want to load and The TreeView that you want to populate.

Copy the following code into a BAS module or even better add the code to a Class module and change the code so the FileName and TreeView arguments are properties instead.

Have Fun!
Joacim Andersson (joacim@programmer.net)

'-------------------------------
Private Sub FillPropBag(pb As PropertyBag, _
  tvw As MSComctlLib.TreeView, Root As MSComctlLib.Node)

	Static nCount As Long
	Dim nde As MSComctlLib.Node
	Dim nIndex As Long

	If pb Is Nothing Then
	Set pb = New PropertyBag
	nCount = 0
	pb.WriteProperty "NumberOfNodes", tvw.Nodes.Count, 0
	End If
	On Error Resume Next
	pb.WriteProperty "Text" & nCount, Root.Text
	nIndex = Root.Parent.Index
	If nCount = 0 Then
	nIndex = 0
	End If
	pb.WriteProperty "Parent" & nCount, nIndex, 0
	pb.WriteProperty "Key" & nCount, Root.Key, ""
	pb.WriteProperty "Index" & nCount, Root.Index, 0
	pb.WriteProperty "Image" & nCount, Root.Image, vbEmpty
	pb.WriteProperty "SelectedImage" & nCount, _
          Root.SelectedImage, vbEmpty
	Set nde = Root.Child
	If nde Is Nothing Then
	Set nde = Root.Next
	If nde Is Nothing Then
		Exit Sub
	End If
	End If
	nCount = nCount + 1
	FillPropBag pb, tvw, nde
End Sub

Public Sub SaveTree(sFilename As String, _
  tvw As MSComctlLib.TreeView, Root As MSComctlLib.Node)
  
  Dim pb As PropertyBag
  Dim bArr() As Byte
  Dim iFile As Integer

  FillPropBag pb, tvw, Root
  iFile = FreeFile
  Open sFilename For Binary Access Write As #iFile
  bArr = pb.Contents
  Put #iFile, , bArr
  Close #iFile
End Sub

Public Sub LoadTree(sFilename As String, _
  tvw As MSComctlLib.TreeView)
  
  Dim pb As PropertyBag
  Dim bArr() As Byte
  Dim iFile As Integer
  Dim nde As MSComctlLib.Node
  Dim nCount As Long
  Dim nNumOfNodes As Long
  Dim nIndex As Long
  Dim sText$, sKey$
  Dim nParent As Long
  Dim vImage, vSelectedImage

  iFile = FreeFile
  Open sFilename For Binary Access Read As #iFile
  ReDim bArr(LOF(iFile)) As Byte
  Get #iFile, , bArr
  Close #iFile
  Set pb = New PropertyBag
  pb.Contents = bArr
  tvw.Nodes.Clear
  nNumOfNodes = pb.ReadProperty("NumberOfNodes", 0)
  If nNumOfNodes = 0 Then
    Exit Sub
  End If
  Do While nCount < nNumOfNodes
    nParent = pb.ReadProperty("Parent" & nCount, 0)
    nIndex = pb.ReadProperty("Index" & nCount, 0)
    sKey = pb.ReadProperty("Key" & nCount, "")
    sText = pb.ReadProperty("Text" & nCount, "")
    vImage = pb.ReadProperty("Image" & nCount, vbEmpty)
    vSelectedImage = pb.ReadProperty("SelectedImage" _
      & nCount, vbEmpty)
    If nParent Then
      tvw.Nodes.Add tvw.Nodes(nParent), tvwChild, sKey, _
        sText, vImage, vSelectedImage
    Else
      tvw.Nodes.Add , , sKey, sText, vImage, vSelectedImage
    End If
    nCount = nCount + 1
  Loop
End Sub