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HierarchicalDataBoundControl Class

Note: This class is new in the .NET Framework version 2.0.

Serves as the base class for all ASP.NET version 2.0 data-bound controls that display their data in hierarchical form.

Namespace: System.Web.UI.WebControls
Assembly: System.Web (in system.web.dll)

'Declaration
Public MustInherit Class HierarchicalDataBoundControl
	Inherits BaseDataBoundControl
'Usage
Dim instance As HierarchicalDataBoundControl

public abstract class HierarchicalDataBoundControl extends BaseDataBoundControl
public abstract class HierarchicalDataBoundControl extends BaseDataBoundControl

The HierarchicalDataBoundControl class is the base class used for ASP.NET controls that retrieve data from an ASP.NET hierarchical data source control and bind user-interface elements of the control to that data for display. The TreeView and Menu classes derive from HierarchicalDataBoundControl.

Page developers do not use the HierarchicalDataBoundControl class directly; instead, they use controls that derive from this class.

Controls developers extend this class to create data-bound controls that work with classes that implement the IHierarchicalDataSource interface and classes that derive from the HierarchicalDataSourceControl and HierarchicalDataSourceView classes. When deriving a class from the HierarchicalDataBoundControl class, override the PerformDataBinding method to bind the user-interface elements of your control to data retrieved by the GetData method. In most cases, the PerformDataBinding method is the only method you will override in your derived class.

For ASP.NET 2.0 data-bound controls, the PerformSelect method is the equivalent of the DataBind method, and is called to bind data at run time. The PerformSelect method calls the GetData and PerformDataBinding methods.

The following code example demonstrates how to derive a class from the HierarchicalDataBoundControl class to create a custom data-bound control. The GeneologyTree control renders a pre HTML section with a text tree for the data retrieved from an associated data source control.

Imports System
Imports System.Collections
Imports System.ComponentModel
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace Samples.AspNet.VB.Controls

    <AspNetHostingPermission(SecurityAction.Demand, _
      Level:=AspNetHostingPermissionLevel.Minimal), _
      AspNetHostingPermission(SecurityAction.InheritanceDemand, _
      Level:=AspNetHostingPermissionLevel.Minimal)> _
    Public Class GeneologyTree
        Inherits HierarchicalDataBoundControl

        Dim MaxDepth As Integer = 0

        Private aRootNode As TreeNode
        Public ReadOnly Property RootNode() As TreeNode
            Get
                If aRootNode Is Nothing Then
                    aRootNode = New TreeNode(String.Empty)
                End If
                Return aRootNode
            End Get
        End Property

        Private alNodes As ArrayList
        Public ReadOnly Property Nodes() As ArrayList
            Get
                If alNodes Is Nothing Then
                    alNodes = New ArrayList()
                End If
                Return alNodes
            End Get
        End Property

        Public Property DataTextField() As String
            Get
                Dim o As Object = ViewState("DataTextField")
                If o Is Nothing Then
                    Return String.Empty
                Else
                    Return CStr(o)
                End If
            End Get
            Set(ByVal value As String)
                ViewState("DataTextField") = value
                If Initialized Then
                    OnDataPropertyChanged()
                End If
            End Set
        End Property

        Protected Overrides Sub PerformDataBinding()
            MyBase.PerformDataBinding()

            ' Do not attempt to bind data if there is no
            ' data source set.
            If Not IsBoundUsingDataSourceID AndAlso DataSource Is Nothing Then
                Return
            End If

            Dim view As HierarchicalDataSourceView = GetData(RootNode.DataPath)

            If view Is Nothing Then
                Throw New InvalidOperationException _
                ("No view returned by data source control.")
            End If

            Dim enumerable As IHierarchicalEnumerable = view.Select()
            If Not (enumerable Is Nothing) Then

                Nodes.Clear()

                Try
                    RecurseDataBindInternal(RootNode, enumerable, 1)
                Finally
                End Try
            End If

        End Sub ' PerformDataBinding

        Private Sub RecurseDataBindInternal(ByVal node As TreeNode, _
            ByVal enumerable As IHierarchicalEnumerable, _
            ByVal depth As Integer)

            Dim item As Object
            For Each item In enumerable

                Dim data As IHierarchyData = enumerable.GetHierarchyData(item)

                If Not data Is Nothing Then

                    ' Create an object that represents the bound data
                    ' to the control.
                    Dim newNode As New TreeNode()
                    Dim rvnode As New RootViewNode()

                    rvnode.Node = newNode
                    rvnode.Depth = depth

                    ' The dataItem is not just a string, but potentially
                    ' an XML node or some other container. 
                    ' If DataTextField is set, use it to determine which 
                    ' field to render. Otherwise, use the first field.                    
                    If DataTextField.Length > 0 Then
                        newNode.Text = DataBinder.GetPropertyValue _
                        (data, DataTextField, Nothing)
                    Else
                        Dim props As PropertyDescriptorCollection = _
                        TypeDescriptor.GetProperties(data)

                        ' Set the "default" value of the node.
                        newNode.Text = String.Empty

                        ' Set the true data-bound value of the TextBox,
                        ' if possible.
                        If props.Count >= 1 Then
                            If Not props(0).GetValue(data) Is Nothing Then
                                newNode.Text = props(0).GetValue(data).ToString()
                            End If
                        End If
                    End If

                    Nodes.Add(rvnode)

                    If data.HasChildren Then
                        Dim newEnumerable As IHierarchicalEnumerable = _
                            data.GetChildren()
                        If Not (newEnumerable Is Nothing) Then
                            RecurseDataBindInternal(newNode, _
                            newEnumerable, depth + 1)
                        End If
                    End If

                    If MaxDepth < depth Then
                        MaxDepth = depth
                    End If
                End If
            Next item

        End Sub 'RecurseDataBindInternal

        Protected Overrides Sub Render(ByVal writer As HtmlTextWriter)

            writer.WriteLine("<PRE>")
            Dim currentDepth As Integer = 1
            Dim currentTextLen As Integer = 0

            Dim rvnode As RootViewNode
            For Each rvnode In Nodes
                If rvnode.Depth = currentDepth Then
                    Dim output As String = "  " + rvnode.Node.Text + "  "
                    writer.Write(output)
                    currentTextLen = currentTextLen + output.Length
                Else
                    writer.WriteLine("")

                    ' Some very basic whitespace formatting.
                    ' The implicit conversion to an Integer is fine, as 
                    ' a general estimate is acceptable for this 
                    ' simple example.
                    Dim halfLine As Integer = CInt(currentTextLen / 2)
                    Dim i As Integer
                    For i = 0 To halfLine
                        writer.Write(" "c)
                    Next i
                    writer.Write("|"c)
                    writer.WriteLine("")
                    currentDepth += 1
                    Dim j As Integer
                    For j = 0 To halfLine
                        writer.Write(" "c)
                    Next j
                    Dim output As String = "  " + rvnode.Node.Text + "  "
                    writer.Write(output)
                    currentTextLen = currentTextLen + output.Length
                End If
            Next rvnode
            writer.WriteLine("</PRE>")

        End Sub 'Render


        Private Class RootViewNode
            Public Node As TreeNode
            Public Depth As Integer
        End Class 'RootViewNode
    End Class 'GeneologyTree
End Namespace

The following code example demonstrates how to use the GeneologyTree control, defined in the previous example, and bind it to an XmlDataSource control.

<%@Page language="VB" %>
<%@ Register TagPrefix="aspSample" 
    Namespace="Samples.AspNet.VB.Controls" 
    Assembly="Samples.AspNet.VB.Controls" %>

<html>
  <head>
    <title>VB Example</title>
  </head>

  <body>
    <form id="Form1" method="post" runat="server">

        <aspSample:geneologytree
          id="GeneologyTree1"
          runat="server"
          datatextfield="title"
          datasourceid="XmlDataSource1" />

        <asp:xmldatasource
          id="XmlDataSource1"
          datafile="geneology.xml"          
          runat="server" />
          
    </form>
  </body>
</html>

The geneology.xml file accessed in the code example contains the following data.

<family>
  <member title="great-grandfather">
    <member title="grandfather" >
      <member title="child" />
      <member title="father" >
         <member title="son" />
      </member>
    </member>
  </member>
</family>

System.Object
   System.Web.UI.Control
     System.Web.UI.WebControls.WebControl
       System.Web.UI.WebControls.BaseDataBoundControl
        System.Web.UI.WebControls.HierarchicalDataBoundControl
           System.Web.UI.WebControls.Menu
           System.Web.UI.WebControls.TreeView

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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