HierarchicalDataBoundControl Classe

Definizione

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

Ereditarietà

Object

Control

WebControl

BaseDataBoundControl

HierarchicalDataBoundControl

Derivato

System.Web.UI.WebControls.Menu

System.Web.UI.WebControls.TreeView

Esempio

Nell'esempio di codice seguente viene illustrato come derivare una classe dalla HierarchicalDataBoundControl classe per creare un controllo associato a dati personalizzato. Il controllo esegue il GeneologyTree rendering di una pre sezione HTML con un albero di testo per i dati recuperati da un controllo origine dati associato.

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

Nell'esempio di codice seguente viene illustrato come usare il GeneologyTree controllo , definito nell'esempio precedente e associarlo a un XmlDataSource controllo .

<%@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>

Il file geneology.xml a cui si accede nell'esempio di codice contiene i dati seguenti.

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

Commenti

La HierarchicalDataBoundControl classe è la classe base utilizzata per ASP.NET controlli che recuperano dati da un controllo origine dati gerarchico ASP.NET e associano gli elementi dell'interfaccia utente del controllo a tali dati per la visualizzazione. Le TreeView classi e Menu derivano da HierarchicalDataBoundControl.

Gli sviluppatori di pagine non usano direttamente la HierarchicalDataBoundControl classe , ma usano invece controlli che derivano da questa classe.

Gli sviluppatori di controlli estendono questa classe per creare controlli associati a dati che funzionano con classi che implementano l'interfaccia IHierarchicalDataSource e le classi che derivano dalle HierarchicalDataSourceControl classi e HierarchicalDataSourceView . Quando si deriva una classe dalla HierarchicalDataBoundControl classe , eseguire l'override del PerformDataBinding metodo per associare gli elementi dell'interfaccia utente del controllo ai dati recuperati dal GetData metodo . Nella maggior parte dei casi, il PerformDataBinding metodo è l'unico metodo di cui si eseguirà l'override nella classe derivata.

Per ASP.NET controlli associati a dati 2.0, il PerformSelect metodo è l'equivalente del DataBind metodo e viene chiamato per associare i dati in fase di esecuzione. Il PerformSelect metodo chiama i GetData metodi e PerformDataBinding .

Costruttori

Proprietà

Metodi

Eventi

Implementazioni dell'interfaccia esplicita

Metodi di estensione

Si applica a