Handling Hierarchical Data with a TreeView in ASP.NET

Imports System
Imports System.Data
Imports System.Web.UI
Imports System.Collections
 
'*********************************************************************** 
' Written By Ralph Varjabedian 
' You may use this code freely and copy this code provided that 
' You do not remove this copyright notice. 
' April 2008 
' http://www.varjabedian.net/archive/2008/04/22/binding-asp.net-treeview-to-a-dataset-or-an-objectdatasource.aspx 
'*********************************************************************** 
 
Namespace TreeViewBindingTest
    ''' <summary> 
    ''' A class that translates a DataSet into IHierarchicalDataSource that can be used to bind Hierarchical data to a TreeView 
    ''' </summary> 
    Public Class HierarchicalDataSet
        Implements IHierarchicalDataSource
        Private dataSet As DataSet
        Private idColumnName As String
        Private parentIdColumnName As String
 
        ''' <summary> 
        ''' The constructor of the class 
        ''' </summary> 
        ''' <param name="dataSet">The dataset that contains the data</param> 
        ''' <param name="idColumnName">The Primary key column name</param> 
        ''' <param name="parentidColumnName">The Parent Primary key column name that identifies the Parent-Child relationship</param> 
        Public Sub New(ByVal dataSet As DataSet, ByVal idColumnName As String, ByVal parentIdColumnName As String)
            Me.dataSet = dataSet
            Me.idColumnName = idColumnName
            Me.parentIdColumnName = parentIdColumnName
        End Sub
 
        Public Event DataSourceChanged(ByVal sender As Object, ByVal e As EventArgs)
        ' never used here 
 
        Public Function GetHierarchicalView(ByVal viewPath As String) As HierarchicalDataSourceView
            Return New DataSourceView(Me, viewPath)
        End Function
 
#Region "supporting methods"
        Private Function GetParentRow(ByVal row As DataRowView) As DataRowView
            dataSet.Tables(0).DefaultView.RowFilter = [String].Format("{0} = {1}", idColumnName, row(parentIdColumnName).ToString())
            Dim parentRow As DataRowView = dataSet.Tables(0).DefaultView(0)
            dataSet.Tables(0).DefaultView.RowFilter = ""
            Return parentRow
        End Function
 
        Private Function GetChildrenViewPath(ByVal viewPath As String, ByVal row As DataRowView) As String
            Return viewPath + "\" + row(idColumnName).ToString()
        End Function
 
        Private Function HasChildren(ByVal row As DataRowView) As Boolean
            dataSet.Tables(0).DefaultView.RowFilter = [String].Format("{0} = {1}", parentIdColumnName, row(idColumnName))
            Dim hasChildren As Boolean = dataSet.Tables(0).DefaultView.Count > 0
            dataSet.Tables(0).DefaultView.RowFilter = ""
            Return hasChildren
        End Function
 
        Private Function GetParentViewPath(ByVal viewPath As String) As String
            Return viewPath.Substring(0, viewPath.LastIndexOf("\"))
        End Function
#End Region
 
#Region "private classes that implement further interfaces"
        Private Class DataSourceView
            Inherits HierarchicalDataSourceView
            Private hDataSet As HierarchicalDataSet
            Private viewPath As String
 
            Public Sub New(ByVal hDataSet As HierarchicalDataSet, ByVal viewPath As String)
                Me.hDataSet = hDataSet
                Me.viewPath = viewPath
            End Sub
 
            Public Overloads Overrides Function [Select]() As IHierarchicalEnumerable
                Return New HierarchicalEnumerable(hDataSet, viewPath)
            End Function
        End Class
 
        Private Class HierarchicalEnumerable
            Implements IHierarchicalEnumerable
            Private hDataSet As HierarchicalDataSet
            Private viewPath As String
 
            Public Sub New(ByVal hDataSet As HierarchicalDataSet, ByVal viewPath As String)
                Me.hDataSet = hDataSet
                Me.viewPath = viewPath
            End Sub
 
            Public Function GetHierarchyData(ByVal enumeratedItem As Object) As IHierarchyData
                Dim row As DataRowView = DirectCast(enumeratedItem, DataRowView)
                Return New HierarchyData(hDataSet, viewPath, row)
            End Function
 
            Public Function GetEnumerator() As IEnumerator
                If viewPath = "" Then
                    hDataSet.dataSet.Tables(0).DefaultView.RowFilter = [String].Format("{0} is null", hDataSet.parentIdColumnName)
                Else
                    Dim lastID As String = viewPath.Substring(viewPath.LastIndexOf("\") + 1)
                    hDataSet.dataSet.Tables(0).DefaultView.RowFilter = [String].Format("{0} = {1}", hDataSet.parentIdColumnName, lastID)
                End If
 
                Dim i As IEnumerator = hDataSet.dataSet.Tables(0).DefaultView.GetEnumerator()
                hDataSet.dataSet.Tables(0).DefaultView.RowFilter = ""
                Return i
            End Function
        End Class
 
        Private Class HierarchyData
            Implements IHierarchyData
            Private hDataSet As HierarchicalDataSet
            Private row As DataRowView
            Private viewPath As String
 
            Public Sub New(ByVal hDataSet As HierarchicalDataSet, ByVal viewPath As String, ByVal row As DataRowView)
                Me.hDataSet = hDataSet
                Me.viewPath = viewPath
                Me.row = row
            End Sub
 
            Public Function GetChildren() As IHierarchicalEnumerable
                Return New HierarchicalEnumerable(hDataSet, hDataSet.GetChildrenViewPath(viewPath, row))
            End Function
 
            Public Function GetParent() As IHierarchyData
                Return New HierarchyData(hDataSet, hDataSet.GetParentViewPath(viewPath), hDataSet.GetParentRow(row))
            End Function
 
            Public ReadOnly Property HasChildren() As Boolean
                Get
                    Return hDataSet.HasChildren(row)
                End Get
            End Property
 
            Public ReadOnly Property Item() As Object
                Get
                    Return row
                End Get
            End Property
 
            Public ReadOnly Property Path() As String
                Get
                    Return viewPath
                End Get
            End Property
 
            Public ReadOnly Property Type() As String
                Get
                    Return GetType(DataRowView).ToString()
                End Get
            End Property
        End Class
#End Region
    End Class
End Namespace