ASPxTreeList.VirtualModeCreateChildren Event

Enables creation of a list of business objects that correspond to the child nodes owned by the processed node (virtual mode).

Namespace: DevExpress.Web.ASPxTreeList

Assembly: DevExpress.Web.ASPxTreeList.v18.2.dll

Declaration

C#

public event TreeListVirtualModeCreateChildrenEventHandler VirtualModeCreateChildren

VB.NET

Public Event VirtualModeCreateChildren As TreeListVirtualModeCreateChildrenEventHandler

Event Data

The VirtualModeCreateChildren event's data class is TreeListVirtualModeCreateChildrenEventArgs. The following properties provide information specific to this event:

Property	Description
Children	Gets or sets the collection of children for the currently processed node object.
NodeObject	Gets the processed node object.

Remarks

In virtual mode a tree is created on demand. In this instance, child nodes are created and initialized when their parent node is expanded.

The ASPxTreeList fires two events that you should process in code. These include:

• VirtualModeCreateChildren
• ASPxTreeList.VirtualModeNodeCreating

Handle the VirtualModeCreateChildren event to create a list of business objects that correspond to the child nodes owned by the processed node. This list should be assigned to the TreeListVirtualModeCreateChildrenEventArgs.Children property.

For detailed information, see Virtual Mode.

Example

In this example, the ASPxTreeList uses the Virtual data binding method to display the file/folder tree. In this mode, a tree is created on demand.

The image below shows the result.

C#

using System.IO;
using System.Collections.Generic;
using DevExpress.Web.ASPxTreeList;

protected void ASPxTreeList1_VirtualModeCreateChildren(object sender,
TreeListVirtualModeCreateChildrenEventArgs e) {
    string path = e.NodeObject == null ? Page.MapPath("~/") : e.NodeObject.ToString();

    List<string> children = new List<string>();
    if (Directory.Exists(path)) {
        foreach (string name in Directory.GetDirectories(path)) {
            if (!IsSystemName(name))
                children.Add(name);
        }
        foreach (string name in Directory.GetFiles(path))
            if (!IsSystemName(name))
                children.Add(name);
    }
    e.Children = children;
}
protected void ASPxTreeList1_VirtualModeNodeCreating(object sender,
TreeListVirtualModeNodeCreatingEventArgs e) {
    string path = e.NodeObject.ToString();

    e.NodeKeyValue = GetNodeGuid(path);
    e.IsLeaf = !Directory.Exists(path);
    e.SetNodeValue("FileName", PopFileName(path));
}

// Helpers

Guid GetNodeGuid(string path) {
    if (!Map.ContainsKey(path))
        Map[path] = Guid.NewGuid();
    return Map[path];
}
Dictionary<string, Guid> Map {
    get {
        const string key = "DX_PATH_GUID_MAP";
        if (Session[key] == null)
            Session[key] = new Dictionary<string, Guid>();
        return Session[key] as Dictionary<string, Guid>;
    }
}
string PopFileName(string path) {
    return path.Substring(1 + path.LastIndexOf("\\"));
}
bool IsSystemName(string name) {
    name = PopFileName(name).ToLower();
    return name.StartsWith("app_") || name == "bin"
        || name.EndsWith(".aspx.cs") || name.EndsWith(".aspx.vb");
}

VB.NET

Imports System.IO
Imports System.Collections.Generic
Imports DevExpress.Web.ASPxTreeList

Protected Sub ASPxTreeList1_VirtualModeCreateChildren(ByVal sender As Object,_
ByVal e As TreeListVirtualModeCreateChildrenEventArgs)
   Dim path As String
   If e.NodeObject Is Nothing Then
   path = Page.MapPath("~/")
   Else
      path = e.NodeObject.ToString()
   End If

   Dim children As List(Of String) = New List(Of String)()
   If Directory.Exists(path) Then
      For Each name As String In Directory.GetDirectories(path)
         If (Not IsSystemName(name)) Then
            children.Add(name)
         End If
      Next name
      For Each name As String In Directory.GetFiles(path)
         If (Not IsSystemName(name)) Then
            children.Add(name)
         End If
      Next name
   End If
   e.Children = children
End Sub

Protected Sub ASPxTreeList1_VirtualModeNodeCreating(ByVal sender As Object,_
ByVal e As TreeListVirtualModeNodeCreatingEventArgs)
   Dim path As String = e.NodeObject.ToString()

   e.NodeKeyValue = GetNodeGuid(path)
   e.IsLeaf = Not Directory.Exists(path)
   e.SetNodeValue("FileName", PopFileName(path))
End Sub

' Helpers

Private Function GetNodeGuid(ByVal path As String) As Guid
   If (Not Map.ContainsKey(path)) Then
      Map(path) = Guid.NewGuid()
   End If
   Return Map(path)
End Function

Private ReadOnly Property Map() As Dictionary(Of String, Guid)
   Get
      Const key As String = "DX_PATH_GUID_MAP"
      If Session(key) Is Nothing Then
         Session(key) = New Dictionary(Of String, Guid)()
      End If
      Return TryCast(Session(key), Dictionary(Of String, Guid))
   End Get
End Property

Private Function PopFileName(ByVal path As String) As String
   Return path.Substring(1 & path.LastIndexOf("\"))
End Function

Private Function IsSystemName(ByVal name As String) As Boolean
   name = PopFileName(name).ToLower()
   Return name.StartsWith("app_") OrElse name = "bin" OrElse name.EndsWith(".aspx.cs")_
   OrElse name.EndsWith(".aspx.vb")
End Function