HierarchicalDataBoundControl Class
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>
- AspNetHostingPermission for operating in a hosted environment. Demand value: LinkDemand; Permission value: Minimal.
- AspNetHostingPermission for operating in a hosted environment. Demand value: InheritanceDemand; Permission value: Minimal.
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
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.