HierarchicalDataBoundControl Klass

Definition

public ref class HierarchicalDataBoundControl abstract : System::Web::UI::WebControls::BaseDataBoundControl

public abstract class HierarchicalDataBoundControl : System.Web.UI.WebControls.BaseDataBoundControl

type HierarchicalDataBoundControl = class
    inherit BaseDataBoundControl

Public MustInherit Class HierarchicalDataBoundControl
Inherits BaseDataBoundControl

Arv

Object

Control

WebControl

BaseDataBoundControl

HierarchicalDataBoundControl

Härledda

System.Web.UI.WebControls.Menu

System.Web.UI.WebControls.TreeView

Exempel

Följande kodexempel visar hur du härleder en klass från HierarchicalDataBoundControl klassen för att skapa en anpassad databunden kontroll. Kontrollen GeneologyTree renderar ett pre HTML-avsnitt med ett textträd för data som hämtats från en associerad datakällkontroll.

using System;
using System.Collections;
using System.ComponentModel;
using System.Security.Permissions;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Samples.AspNet.CS.Controls {

    [AspNetHostingPermission(SecurityAction.Demand, 
        Level=AspNetHostingPermissionLevel.Minimal)]
    [AspNetHostingPermission(SecurityAction.InheritanceDemand, 
        Level=AspNetHostingPermissionLevel.Minimal)]
    public class GeneologyTree : HierarchicalDataBoundControl {

        private TreeNode rootNode;
        public TreeNode RootNode {
            get {
                rootNode ??= new TreeNode(String.Empty);
                return rootNode;
            }
        }
        
        private ArrayList nodes;
        public ArrayList Nodes {
            get {
                if (null == nodes) {
                    nodes = new ArrayList();
                }
                return nodes;
            }
        }
        public string DataTextField {
            get {
                object o = ViewState["DataTextField"];
                return((o == null) ? string.Empty : (string)o);
            }
            set {
                ViewState["DataTextField"] = value;
                if (Initialized) {
                    OnDataPropertyChanged();
                }
            }
        }
        private int _maxDepth = 0;
        protected override void PerformDataBinding() {
            base.PerformDataBinding();

            // Do not attempt to bind data if there is no
            // data source set.
            if (!IsBoundUsingDataSourceID && (DataSource == null)) {
                return;
            }
            
            HierarchicalDataSourceView view = GetData(RootNode.DataPath);
            
            if (view == null) {
                throw new InvalidOperationException
                    ("No view returned by data source control.");
            }                                  
            
            IHierarchicalEnumerable enumerable = view.Select();
            if (enumerable != null) {
                            
                Nodes.Clear();
                                
                try {
                    RecurseDataBindInternal(RootNode, enumerable, 1);
                }
                finally {
                }
            }
        }
        private void RecurseDataBindInternal(TreeNode node, 
            IHierarchicalEnumerable enumerable, int depth) {                                    
                        
            foreach(object item in enumerable) {
                IHierarchyData data = enumerable.GetHierarchyData(item);

                if (null != data) {
                    // Create an object that represents the bound data
                    // to the control.
                    TreeNode newNode = new TreeNode();
                    RootViewNode rvnode = 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) {
                        newNode.Text = DataBinder.GetPropertyValue
                            (data, DataTextField, null);
                    }
                    else {
                        PropertyDescriptorCollection props = 
                            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) {                        
                            if (null != props[0].GetValue(data)) {
                                newNode.Text = 
                                    props[0].GetValue(data).ToString();
                            } 
                        }
                    }

                    Nodes.Add(rvnode);                    
                    
                    if (data.HasChildren) {
                        IHierarchicalEnumerable newEnumerable = 
                            data.GetChildren();
                        if (newEnumerable != null) {                            
                            RecurseDataBindInternal(newNode, 
                                newEnumerable, depth+1 );
                        }
                    }
                    
                    if ( _maxDepth < depth) _maxDepth = depth;
                }
            }
        }
        protected override void Render(HtmlTextWriter writer) {
                        
            writer.WriteLine("<PRE>");                        
            int currentDepth = 1;
            int currentTextLen = 0;
            
            foreach (RootViewNode rvnode in Nodes) {
                if (rvnode.Depth == currentDepth) {
                    string output = "  " + rvnode.Node.Text + "  ";
                    writer.Write(output);
                    currentTextLen = currentTextLen + output.Length;
                }
                else {
                    writer.WriteLine("");
                    // Some very basic white-space formatting
                    int halfLine = currentTextLen / 2;
                    for (int i=0;i<halfLine;i++) {
                        writer.Write(' ');
                    }
                    writer.Write('|');
                    writer.WriteLine("");
                    ++currentDepth; 
                    currentTextLen = 0;
                    for (int j=0;j<halfLine;j++) {
                        writer.Write(' ');
                    }
                    string output = "  " + rvnode.Node.Text + "  ";
                    writer.Write(output);
                    currentTextLen = currentTextLen + output.Length;                    
                }                                                           
            }
            writer.WriteLine("</PRE>");
        }
        
        private class RootViewNode { 
            public TreeNode Node;
            public int Depth;
        }
    }
}

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

        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

        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 white-space 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


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

Följande kodexempel visar hur du GeneologyTree använder kontrollen, definieras i föregående exempel och binder den till en XmlDataSource kontroll.

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

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>C# 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>

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

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
  <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>

Den geneology.xml fil som används i kodexemplet innehåller följande data.

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

Kommentarer

Klassen HierarchicalDataBoundControl är basklassen som används för ASP.NET kontroller som hämtar data från en ASP.NET hierarkisk datakällkontroll och binder användargränssnittselement i kontrollen till dessa data för visning. Klasserna TreeView och Menu härleds från HierarchicalDataBoundControl.

Sidutvecklare använder HierarchicalDataBoundControl inte klassen direkt. I stället använder de kontroller som härleds från den här klassen.

Styr utvecklare utökar den här klassen för att skapa databundna kontroller som fungerar med klasser som implementerar gränssnittet IHierarchicalDataSource och klasserna som härleds från HierarchicalDataSourceControl klasserna och HierarchicalDataSourceView . När du härleder en klass från HierarchicalDataBoundControl klassen åsidosätter PerformDataBinding du metoden för att binda användargränssnittselementen i kontrollen till data som hämtats med GetData metoden. I de flesta fall PerformDataBinding är metoden den enda metod som du åsidosätter i din härledda klass.

För ASP.NET 2.0-databundna kontroller är metoden PerformSelect motsvarigheten till metoden DataBind och anropas för att binda data vid körning. Metoden PerformSelect anropar GetData metoderna och PerformDataBinding .