Tips & Hints - Registering Active X Components (Part 2)

Control - TreeView


	How the TreeView control works Adding Nodes at Runtime Using the Tag Property Sorting Nodes Assigning Images to Nodes Clearing a List Removing Nodes Counting List Entries Getting Selected Node's Index Searching a TreeView Scrolling the List Programmatically

How the TreeView control works


	A TreeView works much differently than a ListBox control. With a TreeView, each item in the list is referred to as a Node, and the list is actually a collection of Nodes. So when you want to access any of the items in the TreeView control, you will have to access the Nodes Collection first. Hopefully the Examples below will clarify this for you...

Adding Nodes at Runtime

There are two ways of adding an item to a TreeView. You can simply run the regular .Add method:

'for parent nodes
TreeView1.Nodes.Add , , "USERS", "Users"
'for child nodes
TreeView1.Nodes.Add "USERS", tvwChild, Name1, "Name 1"

Or you can set an object variable (the most common way and the most preferred) and gain quicker access to the newly added node for any extra tweaking without a lot of hassle.

Dim nItem As Node
Set nItem = TreeView1.Nodes.Add , , "USERS", "Users"

The parameters for the Add method are pretty simple and straightforward.

.Add(relative, relationship, key, text, image, selectedimage)

Arguments	Description
relative*	The index number or key of a pre-existing Node object. Empty if parent node.
relationship*	Specifies the relative placement of the Node object. (See below) Empty if parent node.
key*	A unique string that can be used to retrieve the Node with the Item method.
text	Required. The string that appears in the Node.
image*	The index of an image in an associated ImageList control.
selectedimage*	The index of an image in an associated ImageList control that is shown when the Node is selected.

*Optional

Constant	Value	Description
tvwFirst	0	First. The Node is placed before all other nodes at the same level of the node named in relative.
tvwLast	1	Last. The Node is placed after all other nodes at the same level of the node named in relative. Any Node added subsequently may be placed after one added as Last.
tvwNext	2	(Default) Next. The Node is placed after the node named in relative.
tvwPrevious	3	Previous. The Node is placed before the node named in relative.
tvwChild	4	Child. The Node becomes a child node of the node named in relative.

Although the Key is optional. I would recommend using it. This will make it easier for quicker access during searches and such. The key must be unique for each node. Usually I just use the same as the nodes text but in upper case.

Using the Tag Property

Now if you wish to classify your nodes, then the Tag property can be used. For instance, you have a list of books. You want them all under the same branch but you want to specify which are hard-cover and which are soft-cover. In this case you would use:

Dim nItem As Node
'softcover
Set nItem = TreeView1.Nodes.Add "BOOKS", tvwChild, Name2, "Name 2"
nItem.Tag = "Softcover"
'hardcover
Set nItem = TreeView1.Nodes.Add "BOOKS", tvwChild, Name2, "Name 2"
nItem.Tag = "Hardcover"

Sorting Nodes


	If you wish all the child nodes under a parent to be sorted. Set the parent node's Sorted property to True. Dim nItem As Node Set nItem = TreeView1.Nodes.Add , , "USERS", "Users" nItem.Sorted = True

Assigning Images to Nodes

If you want a little icon in your node you use the Image and the SelectedImage arguments of the Add method. (See 'Adding Nodes at Runtime')

They will accept either a Picture Pointer, such as .Picture of a PictureBox or by using LoadPicture():

TreeView.Nodes.Add , , "USER", "User",LoadPicture ("C:\Pic.bmp")

Or you can associate an ImageList control to the TreeView control, and just use the Index of the image you wish to use.

'add a picture to my ImageList
ImageList1.ListImages.Add , , LoadPicture ("C:\Pic.bmp")
ImageList1.ListImages.Add , , LoadPicture ("C:\Pic2.bmp")

'set the ImageList
Treeview1.ImageList = ImageList1

'add the node
TreeView.Nodes.Add , , "USER", "User", 1, 2

Clearing a list


	To clear a TreeView, use the Clear method for the Nodes Collection: TreeView1.Nodes.Clear

Removing Nodes

Just use the collections Remove method. You just have to know the index of the item you want to remove.

TreeView1.Nodes.Remove (Index)

to remove selected nodes:

TreeView1.Nodes.Remove TreeView1.SelectedItem.Index

Counting list entries

To count entries in a TreeView you can use the collections Count property :

intCount = TreeView1.Nodes.Count

However, this will count all items whether they are a main category or a sub-category item.

If you are wanting to know how many child nodes are under a parent node, then you can use the 'Children' property of the parent node.

intCount = TreeView1.Nodes.Item(1).Children

This is assuming you know the index of the parent node.

And there is one other method of counting nodes. The GetVisibleCount method, which, obvious by its name, counts all visible nodes.

intCount = TreeView1.GetVisibleCount

Getting Selected Node's Index


	intIndex = TreeView1.SelectedItem.Index

Searching a TreeView

There are different ways to do this. A simple way is using a regular For...Each loop. This will loop through each node in the TreeView and set nItem as an object variable to that node.

Dim nItem as Node

For Each nItem in TreeView1.Nodes
'process nItem
Next

'free it up
Set nItem = Nothing

However if you just want to know whether an entry is made already or not then you could use a function like this:

Private Function NameExists(ByVal Name As String) As Boolean
Dim nNode As Node
On Error Resume Next
Set nNode = TreeView1.Nodes.Item(Name)
If Err.Number = 0 Then
NameExists = True
Set nNode = Nothing
End If
End Function

This method uses the 'key' property. So if you didn't use a key, this won't work. It returns a boolean 'True' or 'False' depending on whether or not the node was found. You could alter it and have it return the nodes index instead if you wanted, like so:

Private Function NameExists(ByVal Name As String) As Integer
Dim nNode As Node
On Error Resume Next
Set nNode = TreeView1.Nodes.Item(Name)
If Err.Number = 0 Then
     NameExists = nNode.Index
     Set nNode = Nothing
Else
     NameExists = -1
End If
End Function

This would return the index if found, or -1 if not found.

Scrolling the List Programmatically


	When you add nodes and it scrolls to the end of the list, you can reset it to the beginning of the list (or anywhere you want really), by using the Selected property: TreeView1.Nodes(1).Selected = True