How to Load a Category Tree and Listbox RowSource Type
"Field Value" Property
Overview
In this Access 2000 article, I will show you how to create a category tree and load it into a listbox.
I will demonstrate the steps to create a static value list and associate it with a listbox.
The algorithm can be easily ported to a treeview control or to HTML for an active server page.
Creating the Category Table
- Create a table called "category"
- Include the following fields:
categoryid: autonumber
parentid: number
title: text
- Add the following data values to the category table:
|
Parent ID |
Category ID (autonumber) |
Title |
|
0 |
1 |
Hardware |
|
0 |
2 |
Computers |
|
2 |
3 |
DeskTop |
|
2 |
4 |
Server |
Add a Listbox
- Add a listbox to your form called "lbxCategory"
- Insert the following VB code to the form
- Static values can be added to a listbox
- Each field value is separated with a ";" delimiter
- Rows are determined by the listboxes columncount
- When the ColumnHeads property is set to true, the
first row becomes the column headings
- The RowSourceType settings tell the listbox
control whether the data is dynamically bound to a data table
or static text. In this case, the listbox control is bound to static
text
Option Explicit
Option Compare Database
Dim sFieldValues As String
Private Sub Form_Load()
'Heading Column titles
sFieldValues = "Parent Id;Category Id, Title;"
Call LoadCategory(0)
lbxCategory.RowSourceType = "Value List"
lbxCategory.RowSource = sFieldValues
lbxCategory.ColumnCount = 3
lbxCategory.ColumnHeads = True
End Sub
- The Load Category procedure starts with the root parent id being "0"
- Each category is recursively checked to see if it has children.
Children are concatenated to the sFieldValues string
- Each value list entry is concatenated to the sFieldValue string
embedding the parentid, categoryid, and title information.
Private Sub LoadCategory(sId)
Dim rs As Object
Dim sql
Dim sNewId
'Check for the bottom of the tree
If IsNull(sId) Then
Exit Sub
End If
sql = "select * from category where parentid=" & sId
Set rs = CurrentDb().OpenRecordset(sql)
Do While Not rs.EOF
sFieldValues = sFieldValues & sId & ";" & rs("categoryid") & ";" & rs("title") & ";"
'Recursive call to check for children
Call LoadCategory(rs("categoryid"))
rs.MoveNext
Loop
If Not rs Is Nothing Then
rs.Close
End If
Set rs = Nothing
End Sub
Active Server Page (Tree View)
- Generate a Category tree in HTML.
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